Patent Publication Number: US-10334177-B2

Title: Information communication apparatus, method, and recording medium using switchable normal mode and visible light communication mode

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The application is a continuation of U.S. application Ser. No. 15/860,060, filed Jan. 2, 2018, a continuation of U.S. application Ser. No. 15/161,657, filed May 23, 2016 now U.S. Pat. No. 9,918,016 issued Mar. 13, 2018, which is a continuation of Ser. No. 14/959,264, filed Dec. 4, 2015 now U.S. Pat. No. 9,380,227 issued Jun. 28, 2016, which is a continuation of U.S. application Ser. No. 14/616,091, filed Feb. 6, 2015 now U.S. Pat. No. 9,258,058 issued Feb. 9, 2016, which is a continuation of U.S. application Ser. No. 14/087,639 filed Nov. 22, 2013 now U.S. Pat. No. 8,988,574 issued Mar. 24, 2015, which claims the benefit of U.S. Provisional Patent Application No. 61/746,315 filed on Dec. 27, 2012, Japanese Patent Application No. 2012-286339 filed on Dec. 27, 2012, U.S. Provisional Patent Application No. 61/805,978 filed on Mar. 28, 2013, Japanese Patent Application No. 2013-070740 filed on Mar. 28, 2013, U.S. Provisional Patent Application No. 61/810,291 filed on Apr. 10, 2013, Japanese Patent Application No. 2013-082546 filed on Apr. 10, 2013, is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 13/902,436 filed on May 24, 2013, is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 13/902,215 filed May 24, 2013, is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 13/902,393 filed on May 24, 2013 and claims the benefit of International Patent Application No. PCT/JP2013/003318 filed on May 24, 2013 which claims the benefit of International Patent Application No. PCT/JP2013/003319 filed on May 24, 2013, Japanese Patent Application No. 2013-110445 filed on May 24, 2013, U.S. Provisional Patent Application No. 61/859,902 filed on Jul. 30, 2013, and Japanese Patent Application No. 2013-158359 filed on Jul. 30, 2013, U.S. Provisional Patent Application No. 61/872,028 filed on Aug. 30, 2013, Japanese Patent Application No. 2013-180729 filed on Aug. 30, 2013, U.S. Provisional Patent Application No. 61/895,615 filed Oct. 25, 2013, Japanese Patent Application No. 2013-222827 filed Oct. 25, 2013, U.S. Provisional Patent Application No. 61/896,879 filed Oct. 29, 2013, Japanese Patent Application No. 2013-224805 filed on Oct. 29, 2013, U.S. Provisional Patent Application No. 61/904,611 filed Nov. 15, 2013, Japanese Patent Application No. 2013-237460 filed Nov. 15, 2013. The disclosures of these documents, including the specifications, drawings and claims, are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to a method of communication between a mobile terminal such as a smartphone, a tablet terminal, or a mobile phone and a home electric appliance such as an air conditioner, a lighting device, or a rice cooker. 
     BACKGROUND 
     In recent years, a home-electric-appliance cooperation function has been introduced for a home network, with which various home electric appliances are connected to a network by a home energy management system (HEMS) having a function of managing power usage for addressing an environmental issue, turning power on/off from outside a house, and the like, in addition to cooperation of AV home electric appliances by internet protocol (IP) connection using Ethernet® or wireless local area network (LAN). However, there are home electric appliances whose computational performance is insufficient to have a communication function, and home electric appliances which do not have a communication function due to a matter of cost. 
     In order to solve such a problem, Patent Literature (PTL) 1 discloses a technique of efficiently establishing communication between devices among limited optical spatial transmission devices which transmit information to free space using light, by performing communication using plural single color light sources of illumination light. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Application Publication No. 2002-290335 
     SUMMARY 
     Technical Problem 
     However, the conventional method is limited to a case in which a device to which the method is applied has three color light sources such as an illuminator. The present disclosure solves this problem, and provides an information communication method that enables communication between various devices including a device with low computational performance. 
     Solution to Problem 
     An information communication method according to an aspect of the present disclosure may be an information communication method of obtaining information from a subject, the information communication method including: setting a first exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a plurality of bright lines corresponding to a plurality of exposure lines included in the image sensor appear according to a change in luminance of the subject; obtaining a bright line image including the plurality of bright lines, by capturing the subject changing in luminance by the image sensor with the set first exposure time; and obtaining the information by demodulating data specified by a pattern of the plurality of bright lines included in the obtained bright line image, wherein in the obtaining of a bright line image, exposure starts sequentially for the plurality of exposure lines each at a different time, and exposure of each of the plurality of exposure lines starts after a predetermined blank time elapses from when exposure of an adjacent exposure line adjacent to the exposure line ends. 
     These general and specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of systems, methods, integrated circuits, computer programs, or computer-readable recording media. 
     Advantageous Effects 
     An information communication method disclosed herein enables communication between various devices including a device with low computational performance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG. 1  is a timing diagram of a transmission signal in an information communication device in Embodiment 1. 
         FIG. 2  is a diagram illustrating relations between a transmission signal and a reception signal in Embodiment 1. 
         FIG. 3  is a diagram illustrating relations between a transmission signal and a reception signal in Embodiment 1. 
         FIG. 4  is a diagram illustrating relations between a transmission signal and a reception signal in Embodiment 1. 
         FIG. 5  is a diagram illustrating relations between a transmission signal and a reception signal in Embodiment 1. 
         FIG. 6  is a diagram illustrating relations between a transmission signal and a reception signal in Embodiment 1. 
         FIG. 7  is a diagram illustrating a principle in Embodiment 2. 
         FIG. 8  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 9  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 10  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 11  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 12A  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 12B  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 12C  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 13  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 14  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 15  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 16  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 17  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 18  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 19  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 20  is a diagram illustrating an example of operation in Embodiment 2. 
         FIG. 21  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 22  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 23  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24A  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24B  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24C  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24D  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24E  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24F  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24G  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24H  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 24I  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 25  is a diagram illustrating an example of an observation method of luminance of a light emitting unit in Embodiment 3. 
         FIG. 26  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 27  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 28  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 29  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 30  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 31  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 32  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 33  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 34  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 35  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 36  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 37  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 38  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 39  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 40  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 41  is a diagram illustrating an example of a signal modulation scheme in Embodiment 3. 
         FIG. 42  is a diagram illustrating an example of a light emitting unit detection method in Embodiment 3. 
         FIG. 43  is a diagram illustrating an example of a light emitting unit detection method in Embodiment 3. 
         FIG. 44  is a diagram illustrating an example of a light emitting unit detection method in Embodiment 3. 
         FIG. 45  is a diagram illustrating an example of a light emitting unit detection method in Embodiment 3. 
         FIG. 46  is a diagram illustrating an example of a light emitting unit detection method in Embodiment 3. 
         FIG. 47  is a diagram illustrating transmission signal timelines and an image obtained by capturing light emitting units in Embodiment 3. 
         FIG. 48  is a diagram illustrating an example of signal transmission using a position pattern in Embodiment 3. 
         FIG. 49  is a diagram illustrating an example of a reception device in Embodiment 3. 
         FIG. 50  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 51  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 52  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 53  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 54  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 55  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 56  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 57  is a diagram illustrating an example of a transmission device in Embodiment 3. 
         FIG. 58  is a diagram illustrating an example of a structure of a light emitting unit in Embodiment 3. 
         FIG. 59  is a diagram illustrating an example of a signal carrier in Embodiment 3. 
         FIG. 60  is a diagram illustrating an example of an imaging unit in Embodiment 3. 
         FIG. 61  is a diagram illustrating an example of position estimation of a reception device in Embodiment 3. 
         FIG. 62  is a diagram illustrating an example of position estimation of a reception device in Embodiment 3. 
         FIG. 63  is a diagram illustrating an example of position estimation of a reception device in Embodiment 3. 
         FIG. 64  is a diagram illustrating an example of position estimation of a reception device in Embodiment 3. 
         FIG. 65  is a diagram illustrating an example of position estimation of a reception device in Embodiment 3. 
         FIG. 66  is a diagram illustrating an example of transmission information setting in Embodiment 3. 
         FIG. 67  is a diagram illustrating an example of transmission information setting in Embodiment 3. 
         FIG. 68  is a diagram illustrating an example of transmission information setting in Embodiment 3. 
         FIG. 69  is a block diagram illustrating an example of structural elements of a reception device in Embodiment 3. 
         FIG. 70  is a block diagram illustrating an example of structural elements of a transmission device in Embodiment 3. 
         FIG. 71  is a diagram illustrating an example of a reception procedure in Embodiment 3. 
         FIG. 72  is a diagram illustrating an example of a self-position estimation procedure in Embodiment 3. 
         FIG. 73  is a diagram illustrating an example of a transmission control procedure in Embodiment 3. 
         FIG. 74  is a diagram illustrating an example of a transmission control procedure in Embodiment 3. 
         FIG. 75  is a diagram illustrating an example of a transmission control procedure in Embodiment 3. 
         FIG. 76  is a diagram illustrating an example of information provision inside a station in Embodiment 3. 
         FIG. 77  is a diagram illustrating an example of a passenger service in Embodiment 3. 
         FIG. 78  is a diagram illustrating an example of an in-store service in Embodiment 3. 
         FIG. 79  is a diagram illustrating an example of wireless connection establishment in Embodiment 3. 
         FIG. 80  is a diagram illustrating an example of communication range adjustment in Embodiment 3. 
         FIG. 81  is a diagram illustrating an example of indoor use in Embodiment 3. 
         FIG. 82  is a diagram illustrating an example of outdoor use in Embodiment 3. 
         FIG. 83  is a diagram illustrating an example of route indication in Embodiment 3. 
         FIG. 84  is a diagram illustrating an example of use of a plurality of imaging devices in Embodiment 3. 
         FIG. 85  is a diagram illustrating an example of transmission device autonomous control in Embodiment 3. 
         FIG. 86  is a diagram illustrating an example of transmission information setting in Embodiment 3. 
         FIG. 87  is a diagram illustrating an example of transmission information setting in Embodiment 3. 
         FIG. 88  is a diagram illustrating an example of transmission information setting in Embodiment 3. 
         FIG. 89  is a diagram illustrating an example of combination with 2D barcode in Embodiment 3. 
         FIG. 90  is a diagram illustrating an example of map generation and use in Embodiment 3. 
         FIG. 91  is a diagram illustrating an example of electronic device state obtainment and operation in Embodiment 3. 
         FIG. 92  is a diagram illustrating an example of electronic device recognition in Embodiment 3. 
         FIG. 93  is a diagram illustrating an example of augmented reality object display in Embodiment 3. 
         FIG. 94  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 95  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 96  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 97  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 98  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 99  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 100  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 101  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 102  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 103  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 104  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 105  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 106  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 107  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 108  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 109  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 110  is a diagram illustrating an example of a user interface in Embodiment 3. 
         FIG. 111  is a diagram illustrating an example of application to ITS in Embodiment 4. 
         FIG. 112  is a diagram illustrating an example of application to ITS in Embodiment 4. 
         FIG. 113  is a diagram illustrating an example of application to a position information reporting system and a facility system in Embodiment 4. 
         FIG. 114  is a diagram illustrating an example of application to a supermarket system in Embodiment 4. 
         FIG. 115  is a diagram illustrating an example of application to communication between a mobile phone terminal and a camera in Embodiment 4. 
         FIG. 116  is a diagram illustrating an example of application to underwater communication in Embodiment 4. 
         FIG. 117  is a diagram for describing an example of service provision to a user in Embodiment 5. 
         FIG. 118  is a diagram for describing an example of service provision to a user in Embodiment 5. 
         FIG. 119  is a flowchart illustrating the case where a receiver simultaneously processes a plurality of signals received from transmitters in Embodiment 5. 
         FIG. 120  is a diagram illustrating an example of the case of realizing inter-device communication by two-way communication in Embodiment 5. 
         FIG. 121  is a diagram for describing a service using directivity characteristics in Embodiment 5. 
         FIG. 122  is a diagram for describing another example of service provision to a user in Embodiment 5. 
         FIG. 123  is a diagram illustrating a format example of a signal included in a light source emitted from a transmitter in Embodiment 5. 
         FIG. 124  is a diagram illustrating an example of an environment in a house in Embodiment 6. 
         FIG. 125  is a diagram illustrating an example of communication between a smartphone and home electric appliances according to Embodiment 6. 
         FIG. 126  is a diagram illustrating an example of a configuration of a transmitter device according to Embodiment 6. 
         FIG. 127  is a diagram illustrating an example of a configuration of a receiver device according to Embodiment 6. 
         FIG. 128  is a diagram illustrating a flow of processing of transmitting information to the receiver device by blinking an LED of the transmitter device according to Embodiment 6. 
         FIG. 129  is a diagram illustrating a flow of processing of transmitting information to the receiver device by blinking an LED of the transmitter device according to Embodiment 6. 
         FIG. 130  is a diagram illustrating a flow of processing of transmitting information to the receiver device by blinking an LED of the transmitter device according to Embodiment 6. 
         FIG. 131  is a diagram illustrating a flow of processing of transmitting information to the receiver device by blinking an LED of the transmitter device according to Embodiment 6. 
         FIG. 132  is a diagram illustrating a flow of processing of transmitting information to the receiver device by blinking an LED of the transmitter device according to Embodiment 6. 
         FIG. 133  is a diagram for describing a procedure of performing communication between a user and a device using visible light according to Embodiment 7. 
         FIG. 134  is a diagram for describing a procedure of performing communication between the user and the device using visible light according to Embodiment 7. 
         FIG. 135  is a diagram for describing a procedure from when a user purchases a device until when the user makes initial settings of the device according to Embodiment 7. 
         FIG. 136  is a diagram for describing service exclusively performed by a serviceman when a device fails according to Embodiment 7. 
         FIG. 137  is a diagram for describing service for checking a cleaning state using a cleaner and visible light communication according to Embodiment 7. 
         FIG. 138  is a schematic diagram of home delivery service support using optical communication according to Embodiment 8. 
         FIG. 139  is a flowchart for describing home delivery service support using optical communication according to Embodiment 8. 
         FIG. 140  is a flowchart for describing home delivery service support using optical communication according to Embodiment 8. 
         FIG. 141  is a flowchart for describing home delivery service support using optical communication according to Embodiment 8. 
         FIG. 142  is a flowchart for describing home delivery service support using optical communication according to Embodiment 8. 
         FIG. 143  is a flowchart for describing home delivery service support using optical communication according to Embodiment 8. 
         FIG. 144  is a flowchart for describing home delivery service support using optical communication according to Embodiment 8. 
         FIG. 145  is a diagram for describing processing of registering a user and a mobile phone in use to a server according to Embodiment 9. 
         FIG. 146  is a diagram for describing processing of analyzing user voice characteristics according to Embodiment 9. 
         FIG. 147  is a diagram for describing processing of preparing sound recognition processing according to Embodiment 9. 
         FIG. 148  is a diagram for describing processing of collecting sound by a sound collecting device in the vicinity according to Embodiment 9. 
         FIG. 149  is a diagram for describing processing of analyzing environmental sound characteristics according to Embodiment 9. 
         FIG. 150  is a diagram for describing processing of canceling sound from a sound output device which is present in the vicinity according to Embodiment 9. 
         FIG. 151  is a diagram for describing processing of selecting what to cook and setting detailed operation of a microwave according to Embodiment 9. 
         FIG. 152  is a diagram for describing processing of obtaining notification sound for the microwave from a DB of a server, for instance, and setting the sound in the microwave according to Embodiment 9. 
         FIG. 153  is a diagram for describing processing of adjusting notification sound of the microwave according to Embodiment 9. 
         FIG. 154  is a diagram illustrating examples of waveforms of notification sounds set in the microwave according to Embodiment 9. 
         FIG. 155  is a diagram for describing processing of displaying details of cooking according to Embodiment 9. 
         FIG. 156  is a diagram for describing processing of recognizing notification sound of the microwave according to Embodiment 9. 
         FIG. 157  is a diagram for describing processing of collecting sound by a sound collecting device in the vicinity and recognizing notification sound of the microwave according to Embodiment 9. 
         FIG. 158  is a diagram for describing processing of notifying a user of the end of operation of the microwave according to Embodiment 9. 
         FIG. 159  is a diagram for describing processing of checking an operation state of a mobile phone according to Embodiment 9. 
         FIG. 160  is a diagram for describing processing of tracking a user position according to Embodiment 9. 
         FIG. 161  is a diagram illustrating that while canceling sound from a sound output device, notification sound of a home electric appliance is recognized, an electronic device which can communicate is caused to recognize a current position of a user (operator), and based on the recognition result of the user position, a device located near the user position is caused to give a notification to the user. 
         FIG. 162  is a diagram illustrating content of a database held in the server, the mobile phone, or the microwave according to Embodiment 9. 
         FIG. 163  is a diagram illustrating that a user cooks based on cooking processes displayed on a mobile phone, and further operates the display content of the mobile phone by saying “next”, “return”, and others, according to Embodiment 9. 
         FIG. 164  is a diagram illustrating that the user has moved to another place while he/she is waiting until the operation of the microwave ends after starting the operation or while he/she is stewing food according to Embodiment 9. 
         FIG. 165  is a diagram illustrating that a mobile phone transmits an instruction to detect a user to a device which is connected to the mobile phone via a network, and can recognize a position of the user and the presence of the user, such as a camera, a microphone, or a human sensing sensor. 
         FIG. 166  is a diagram illustrating that a user face is recognized using a camera included in a television, and further the movement and presence of the user are recognized using a human sensing sensor of an air-conditioner, as an example of user detection according to Embodiment 9. 
         FIG. 167  is a diagram illustrating that devices which have detected the user transmit to the mobile phone the detection of the user and a relative position of the user to the devices which have detected the user. 
         FIG. 168  is a diagram illustrating that the mobile phone recognizes microwave operation end sound according to Embodiment 9. 
         FIG. 169  is a diagram illustrating that the mobile phone which has recognized the end of the operation of the microwave transmits an instruction to, among the devices which have detected the user, a device having a screen-display function and a sound output function to notify the user of the end of the microwave operation. 
         FIG. 170  is a diagram illustrating that the device which has received an instruction notifies the user of the details of the notification. 
         FIG. 171  is a diagram illustrating that a device which is present near the microwave, is connected to the mobile phone via a network, and includes a microphone recognizes the microwave operation end sound. 
         FIG. 172  is a diagram illustrating that the device which has recognized the end of operation of the microwave notifies the mobile phone thereof. 
         FIG. 173  is a diagram illustrating that if the mobile phone is near the user when the mobile phone receives the notification indicating the end of the operation of the microwave, the user is notified of the end of the operation of the microwave, using screen display, sound output, and the like by the mobile phone. 
         FIG. 174  is a diagram illustrating that the user is notified of the end of the operation of the microwave. 
         FIG. 175  is a diagram illustrating that the user who has received the notification indicating the end of the operation of the microwave moves to a kitchen. 
         FIG. 176  is a diagram illustrating that the microwave transmits information such as the end of operation to the mobile phone by wireless communication, the mobile phone gives a notification instruction to the television which the user is watching, and the user is notified by a screen display and sound of the television. 
         FIG. 177  is a diagram illustrating that the microwave transmits information such as the end of operation to the television which the user is watching by wireless communication, and the user is notified thereof using the screen display and sound of the television. 
         FIG. 178  is a diagram illustrating that the user is notified by the screen display and sound of the television. 
         FIG. 179  is a diagram illustrating that a user who is at a remote place is notified of information. 
         FIG. 180  is a diagram illustrating that if the microwave cannot directly communicate with the mobile phone serving as a hub, the microwave transmits information to the mobile phone via a personal computer, for instance. 
         FIG. 181  is a diagram illustrating that the mobile phone which has received communication in  FIG. 180  transmits information such as an operation instruction to the microwave, following the information-and-communication path in an opposite direction. 
         FIG. 182  is a diagram illustrating that in the case where the air-conditioner which is an information source device cannot directly communicate with the mobile phone serving as a hub, the air-conditioner notifies the user of information. 
         FIG. 183  is a diagram for describing a system utilizing a communication device which uses a 700 to 900 MHz radio wave. 
         FIG. 184  is a diagram illustrating that a mobile phone at a remote place notifies a user of information. 
         FIG. 185  is a diagram illustrating that the mobile phone at a remote place notifies the user of information. 
         FIG. 186  is a diagram illustrating that in a similar case to that of  FIG. 185 , a television on the second floor serves as a relay device instead of a device which relays communication between a notification recognition device and an information notification device. 
         FIG. 187  is a diagram illustrating an example of an environment in a house in Embodiment 10. 
         FIG. 188  is a diagram illustrating an example of communication between a smartphone and home electric appliances according to Embodiment 10. 
         FIG. 189  is a diagram illustrating a configuration of a transmitter device according to Embodiment 10. 
         FIG. 190  is a diagram illustrating a configuration of a receiver device according to Embodiment 10. 
         FIG. 191  is a sequence diagram for when a transmitter terminal (TV) performs wireless LAN authentication with a receiver terminal (tablet terminal), using optical communication in  FIG. 187 . 
         FIG. 192  is a sequence diagram for when authentication is performed using an application according to Embodiment 10. 
         FIG. 193  is a flowchart illustrating operation of the transmitter terminal according to Embodiment 10. 
         FIG. 194  is a flowchart illustrating operation of the receiver terminal according to Embodiment 10. 
         FIG. 195  is a sequence diagram in which a mobile AV terminal  1  transmits data to a mobile AV terminal  2  according to Embodiment 11. 
         FIG. 196  is a diagram illustrating a screen changed when the mobile AV terminal  1  transmits data to the mobile AV terminal  2  according to Embodiment 11. 
         FIG. 197  is a diagram illustrating a screen changed when the mobile AV terminal  1  transmits data to the mobile AV terminal  2  according to Embodiment 11. 
         FIG. 198  is a system outline diagram for when the mobile AV terminal  1  is a digital camera according to Embodiment 11. 
         FIG. 199  is a system outline diagram for when the mobile AV terminal  1  is a digital camera according to Embodiment 11. 
         FIG. 200  is a system outline diagram for when the mobile AV terminal  1  is a digital camera according to Embodiment 11. 
         FIG. 201  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 202  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 203  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 204  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 205  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 206  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 207  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 208  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 209  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 210  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 211  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 212  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 213  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 214  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 215  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 216  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 217  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 218  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 219  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 220  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 221  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 222  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 223  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 224  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 225  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 226  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 227  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 228  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 229  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 230  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 231  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 232  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 233  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 234  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 235  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 236  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 237  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 238  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 239  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 240  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 241  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 242  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 243  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 244  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 245  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 246  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 247  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 248  is a diagram illustrating a luminance change of a transmitter in Embodiment 12. 
         FIG. 249  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 250  is a diagram illustrating a luminance change of a transmitter in Embodiment 12. 
         FIG. 251  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 252  is a diagram illustrating a luminance change of a transmitter in Embodiment 12. 
         FIG. 253  is a flowchart illustrating an example of processing operation of a transmitter in Embodiment 12. 
         FIG. 254  is a diagram illustrating a luminance change of a transmitter in Embodiment 12. 
         FIG. 255  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 256  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 257  is a flowchart illustrating an example of processing operation of a transmitter in Embodiment 12. 
         FIG. 258  is a diagram illustrating an example of a structure of a transmitter in Embodiment 12. 
         FIG. 259  is a diagram illustrating an example of a structure of a transmitter in Embodiment 12. 
         FIG. 260  is a diagram illustrating an example of a structure of a transmitter in Embodiment 12. 
         FIG. 261  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 262  is a diagram illustrating an example of display and imaging by a receiver and a transmitter in Embodiment 12. 
         FIG. 263  is a flowchart illustrating an example of processing operation of a transmitter in Embodiment 12. 
         FIG. 264  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 265  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 266  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 267  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 268  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 269  is a diagram illustrating a state of a receiver in Embodiment 12. 
         FIG. 270  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 271  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 272  is a diagram illustrating an example of a wavelength of a transmitter in Embodiment 12. 
         FIG. 273  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 274  is a diagram illustrating an example of a structure of a system including a receiver and a transmitter in Embodiment 12. 
         FIG. 275  is a flowchart illustrating an example of processing operation of a system in Embodiment 12. 
         FIG. 276  is a diagram illustrating an example of a structure of a system including a receiver and a transmitter in Embodiment 12. 
         FIG. 277  is a flowchart illustrating an example of processing operation of a system in Embodiment 12. 
         FIG. 278  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 279  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 280  is a diagram illustrating an example of a structure of a system including a receiver and a transmitter in Embodiment 12. 
         FIG. 281  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 282  is a diagram illustrating an example of application of a receiver and a transmitter in Embodiment 12. 
         FIG. 283  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 284  is a diagram illustrating an example of a structure of a system including a receiver and a transmitter in Embodiment 12. 
         FIG. 285  is a flowchart illustrating an example of processing operation of a system in Embodiment 12. 
         FIG. 286  is a flowchart illustrating an example of processing operation of a receiver in Embodiment 12. 
         FIG. 287A  is a diagram illustrating an example of a structure of a transmitter in Embodiment 12. 
         FIG. 287B  is a diagram illustrating another example of a structure of a transmitter in Embodiment 12. 
         FIG. 288  is a flowchart illustrating an example of processing operation of a receiver and a transmitter in Embodiment 12. 
         FIG. 289  is a flowchart illustrating an example of processing operation relating to a receiver and a transmitter in Embodiment 13. 
         FIG. 290  is a flowchart illustrating an example of processing operation relating to a receiver and a transmitter in Embodiment 13. 
         FIG. 291  is a flowchart illustrating an example of processing operation relating to a receiver and a transmitter in Embodiment 13. 
         FIG. 292  is a flowchart illustrating an example of processing operation relating to a receiver and a transmitter in Embodiment 13. 
         FIG. 293  is a flowchart illustrating an example of processing operation relating to a receiver and a transmitter in Embodiment 13. 
         FIG. 294  is a diagram illustrating an example of application of a transmitter in Embodiment 13. 
         FIG. 295  is a diagram illustrating an example of application of a transmitter in Embodiment 13. 
         FIG. 296  is a diagram illustrating an example of application of a transmitter in Embodiment 13. 
         FIG. 297  is a diagram illustrating an example of application of a transmitter and a receiver in Embodiment 13. 
         FIG. 298  is a diagram illustrating an example of application of a transmitter and a receiver in Embodiment 13. 
         FIG. 299  is a diagram illustrating an example of application of a transmitter and a receiver in Embodiment 13. 
         FIG. 300  is a diagram illustrating an example of application of a transmitter and a receiver in Embodiment 13. 
         FIG. 301A  is a diagram illustrating an example of a transmission signal in Embodiment 13. 
         FIG. 301B  is a diagram illustrating another example of a transmission signal in Embodiment 13. 
         FIG. 302  is a diagram illustrating an example of a transmission signal in Embodiment 13. 
         FIG. 303A  is a diagram illustrating an example of a transmission signal in Embodiment 13. 
         FIG. 303B  is a diagram illustrating another example of a transmission signal in Embodiment 13. 
         FIG. 304  is a diagram illustrating an example of a transmission signal in Embodiment 13. 
         FIG. 305A  is a diagram illustrating an example of a transmission signal in Embodiment 13. 
         FIG. 305B  is a diagram illustrating an example of a transmission signal in Embodiment 13. 
         FIG. 306  is a diagram illustrating an example of application of a transmitter in Embodiment 13. 
         FIG. 307  is a diagram illustrating an example of application of a transmitter in Embodiment 13. 
         FIG. 308  is a diagram for describing an imaging element in Embodiment 13. 
         FIG. 309  is a diagram for describing an imaging element in Embodiment 13. 
         FIG. 310  is a diagram for describing an imaging element in Embodiment 13. 
         FIG. 311A  is a flowchart illustrating processing operation of a reception device (imaging device) in a variation of each embodiment. 
         FIG. 311B  is a diagram illustrating a normal imaging mode and a macro imaging mode in a variation of each embodiment in comparison. 
         FIG. 312  is a diagram illustrating a display device for displaying video and the like in a variation of each embodiment. 
         FIG. 313  is a diagram illustrating an example of processing operation of a display device in a variation of each embodiment. 
         FIG. 314  is a diagram illustrating an example of a part transmitting a signal in a display device in a variation of each embodiment. 
         FIG. 315  is a diagram illustrating another example of processing operation of a display device in a variation of each embodiment. 
         FIG. 316  is a diagram illustrating another example of a part transmitting a signal in a display device in a variation of each embodiment. 
         FIG. 317  is a diagram illustrating yet another example of processing operation of a display device in a variation of each embodiment. 
         FIG. 318  is a diagram illustrating a structure of a communication system including a transmitter and a receiver in a variation of each embodiment. 
         FIG. 319  is a flowchart illustrating processing operation of a communication system in a variation of each embodiment. 
         FIG. 320  is a diagram illustrating an example of signal transmission in a variation of each embodiment. 
         FIG. 321  is a diagram illustrating an example of signal transmission in a variation of each embodiment. 
         FIG. 322  is a diagram illustrating an example of signal transmission in a variation of each embodiment. 
         FIG. 323A  is a diagram illustrating an example of signal transmission in a variation of each embodiment. 
         FIG. 323B  is a diagram illustrating an example of signal transmission in a variation of each embodiment. 
         FIG. 323C  is a diagram illustrating an example of signal transmission in a variation of each embodiment. 
         FIG. 323D  is a flowchart illustrating processing operation of a communication system including a receiver and a display or a projector in a variation of each embodiment. 
         FIG. 324  is a diagram illustrating an example of a transmission signal in a variation of each embodiment. 
         FIG. 325  is a diagram illustrating an example of a transmission signal in a variation of each embodiment. 
         FIG. 326  is a diagram illustrating an example of a transmission signal in a variation of each embodiment. 
         FIG. 327A  is a diagram illustrating an example of an imaging element of a receiver in a variation of each embodiment. 
         FIG. 327B  is a diagram illustrating an example of a structure of an internal circuit of an imaging device of a receiver in a variation of each embodiment. 
         FIG. 327C  is a diagram illustrating an example of a transmission signal in a variation of each embodiment. 
         FIG. 327D  is a diagram illustrating an example of a transmission signal in a variation of each embodiment. 
         FIG. 328A  is a diagram for describing an imaging mode of a receiver in a variation of each embodiment. 
         FIG. 328B  is a flowchart illustrating processing operation of a receiver using a special imaging mode A in a variation of each embodiment. 
         FIG. 329A  is a diagram for describing another imaging mode of a receiver in a variation of each embodiment. 
         FIG. 329B  is a flowchart illustrating processing operation of a receiver using a special imaging mode B in a variation of each embodiment. 
         FIG. 330A  is a diagram for describing yet another imaging mode of a receiver in a variation of each embodiment. 
         FIG. 330B  is a flowchart illustrating processing operation of a receiver using a special imaging mode C in a variation of each embodiment. 
         FIG. 331A  is a flowchart of an information communication method according to an aspect of the present disclosure. 
         FIG. 331B  is a block diagram of an information communication device according to an aspect of the present disclosure. 
         FIG. 331C  is a flowchart of an information communication method according to an aspect of the present disclosure. 
         FIG. 331D  is a block diagram of an information communication device according to an aspect of the present disclosure. 
         FIG. 332  is a diagram illustrating an example of an image obtained by an information communication method according to an aspect of the present disclosure. 
         FIG. 333A  is a flowchart of an information communication method according to another aspect of the present disclosure. 
         FIG. 333B  is a block diagram of an information communication device according to another aspect of the present disclosure. 
         FIG. 334A  is a flowchart of an information communication method according to yet another aspect of the present disclosure. 
         FIG. 334B  is a block diagram of an information communication device according to yet another aspect of the present disclosure. 
         FIG. 335  is a diagram illustrating an example of each mode of a receiver in Embodiment 14. 
         FIG. 336  is a diagram illustrating an example of imaging operation of a receiver in Embodiment 14. 
         FIG. 337  is a diagram illustrating another example of imaging operation of a receiver in Embodiment 14. 
         FIG. 338A  is a diagram illustrating another example of imaging operation of a receiver in Embodiment 14. 
         FIG. 338B  is a diagram illustrating another example of imaging operation of a receiver in Embodiment 14. 
         FIG. 338C  is a diagram illustrating another example of imaging operation of a receiver in Embodiment 14. 
         FIG. 339A  is a diagram illustrating an example of camera arrangement of a receiver in Embodiment 14. 
         FIG. 339B  is a diagram illustrating another example of camera arrangement of a receiver in Embodiment 14. 
         FIG. 340  is a diagram illustrating an example of display operation of a receiver in Embodiment 14. 
         FIG. 341  is a diagram illustrating an example of display operation of a receiver in Embodiment 14. 
         FIG. 342  is a diagram illustrating an example of operation of a receiver in Embodiment 14. 
         FIG. 343  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 344  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 345  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 346  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 347  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 348  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 349  is a diagram illustrating an example of operation of a receiver, a transmitter, and a server in Embodiment 14. 
         FIG. 350  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 351  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 352  is a diagram illustrating an example of initial setting of a receiver in Embodiment 14. 
         FIG. 353  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 354  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 355  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 356  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 357  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 358  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 359A  is a diagram illustrating a pen used to operate a receiver in Embodiment 14. 
         FIG. 359B  is a diagram illustrating operation of a receiver using a pen in Embodiment 14. 
         FIG. 360  is a diagram illustrating an example of appearance of a receiver in Embodiment 14. 
         FIG. 361  is a diagram illustrating another example of appearance of a receiver in Embodiment 14. 
         FIG. 362  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 363A  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 363B  is a diagram illustrating an example of application using a receiver in Embodiment 14. 
         FIG. 364A  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 364B  is a diagram illustrating an example of application using a receiver in Embodiment 14. 
         FIG. 365A  is a diagram illustrating an example of operation of a transmitter in Embodiment 14. 
         FIG. 365B  is a diagram illustrating another example of operation of a transmitter in Embodiment 14. 
         FIG. 366  is a diagram illustrating another example of operation of a transmitter in Embodiment 14. 
         FIG. 367  is a diagram illustrating another example of operation of a transmitter in Embodiment 14. 
         FIG. 368  is a diagram illustrating an example of communication form between a plurality of transmitters and a receiver in Embodiment 14. 
         FIG. 369  is a diagram illustrating an example of operation of a plurality of transmitters in Embodiment 14. 
         FIG. 370  is a diagram illustrating another example of communication form between a plurality of transmitters and a receiver in Embodiment 14. 
         FIG. 371  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 372  is a diagram illustrating an example of application of a receiver in Embodiment 14. 
         FIG. 373  is a diagram illustrating an example of application of a receiver in Embodiment 14. 
         FIG. 374  is a diagram illustrating an example of application of a receiver in Embodiment 14. 
         FIG. 375  is a diagram illustrating an example of application of a transmitter in Embodiment 14. 
         FIG. 376  is a diagram illustrating an example of application of a transmitter in Embodiment 14. 
         FIG. 377  is a diagram illustrating an example of application of a reception method in Embodiment 14. 
         FIG. 378  is a diagram illustrating an example of application of a transmitter in Embodiment 14. 
         FIG. 379  is a diagram illustrating an example of application of a transmitter in Embodiment 14. 
         FIG. 380  is a diagram illustrating an example of application of a transmitter in Embodiment 14. 
         FIG. 381  is a diagram illustrating another example of operation of a receiver in Embodiment 14. 
         FIG. 382  is a flowchart illustrating an example of operation of a receiver in Embodiment 15. 
         FIG. 383  is a flowchart illustrating another example of operation of a receiver in Embodiment 15. 
         FIG. 384A  is a block diagram illustrating an example of a transmitter in Embodiment 15. 
         FIG. 384B  is a block diagram illustrating another example of a transmitter in Embodiment 15. 
         FIG. 385  is a diagram illustrating an example of a structure of a system including a plurality of transmitters in Embodiment 15. 
         FIG. 386  is a block diagram illustrating another example of a transmitter in Embodiment 15. 
         FIG. 387A  is a diagram illustrating an example of a transmitter in Embodiment 15. 
         FIG. 387B  is a diagram illustrating an example of a transmitter in Embodiment 15. 
         FIG. 387C  is a diagram illustrating an example of a transmitter in Embodiment 15. 
         FIG. 388A  is a diagram illustrating an example of a transmitter in Embodiment 15. 
         FIG. 388B  is a diagram illustrating an example of a transmitter in Embodiment 15. 
         FIG. 389  is a diagram illustrating an example of processing operation of a receiver, a transmitter, and a server in Embodiment 15. 
         FIG. 390  is a diagram illustrating an example of processing operation of a receiver, a transmitter, and a server in Embodiment 15. 
         FIG. 391  is a diagram illustrating an example of processing operation of a receiver, a transmitter, and a server in Embodiment 15. 
         FIG. 392A  is a diagram for describing synchronization between a plurality of transmitters in Embodiment 15. 
         FIG. 392B  is a diagram for describing synchronization between a plurality of transmitters in Embodiment 15. 
         FIG. 393  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 394  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 395  is a diagram illustrating an example of operation of a transmitter, a receiver, and a server in Embodiment 15. 
         FIG. 396  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 397  is a diagram illustrating an example of appearance of a receiver in Embodiment 15. 
         FIG. 398  is a diagram illustrating an example of operation of a transmitter, a receiver, and a server in Embodiment 15. 
         FIG. 399  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 400  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 401  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 402  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
         FIG. 403A  is a diagram illustrating an example of a structure of information transmitted by a transmitter in Embodiment 15. 
         FIG. 403B  is a diagram illustrating another example of a structure of information transmitted by a transmitter in Embodiment 15. 
         FIG. 404  is a diagram illustrating an example of a 4-value PPM modulation scheme by a transmitter in Embodiment 15. 
         FIG. 405  is a diagram illustrating an example of a PPM modulation scheme by a transmitter in Embodiment 15. 
         FIG. 406  is a diagram illustrating an example of a PPM modulation scheme by a transmitter in Embodiment 15. 
         FIG. 407A  is a diagram illustrating an example of a luminance change pattern corresponding to a header (preamble unit) in Embodiment 15. 
         FIG. 407B  is a diagram illustrating an example of a luminance change pattern in Embodiment 15. 
         FIG. 408A  is a diagram illustrating an example of a luminance change pattern in Embodiment 15. 
         FIG. 408B  is a diagram illustrating an example of a luminance change pattern in Embodiment 15. 
         FIG. 409  is a diagram illustrating an example of operation of a receiver in an in-front-of-store situation in Embodiment 16. 
         FIG. 410  is a diagram illustrating another example of operation of a receiver in an in-front-of-store situation in Embodiment 16. 
         FIG. 411  is a diagram illustrating an example of next operation of a receiver in an in-front-of-store situation in Embodiment 16. 
         FIG. 412  is a diagram illustrating an example of next operation of a receiver in an in-front-of-store situation in Embodiment 16. 
         FIG. 413  is a diagram illustrating an example of next operation of a receiver in an in-front-of-store situation in Embodiment 16. 
         FIG. 414  is a diagram illustrating an example of operation of a display device in an in-store situation in Embodiment 16. 
         FIG. 415  is a diagram illustrating an example of next operation of a display device in an in-store situation in Embodiment 16. 
         FIG. 416  is a diagram illustrating an example of next operation of a display device in an in-store situation in Embodiment 16. 
         FIG. 417  is a diagram illustrating an example of next operation of a receiver in an in-store situation in Embodiment 16. 
         FIG. 418  is a diagram illustrating an example of next operation of a receiver in an in-store situation in Embodiment 16. 
         FIG. 419  is a diagram illustrating an example of next operation of a receiver in an in-store situation in Embodiment 16. 
         FIG. 420  is a diagram illustrating an example of next operation of a receiver in an in-store situation in Embodiment 16. 
         FIG. 421  is a diagram illustrating an example of next operation of a receiver in an in-store situation in Embodiment 16. 
         FIG. 422  is a diagram illustrating an example of next operation of a receiver in an in-store situation in Embodiment 16. 
         FIG. 423  is a diagram illustrating an example of operation of a receiver in a store search situation in Embodiment 16. 
         FIG. 424  is a diagram illustrating an example of next operation of a receiver in a store search situation in Embodiment 16. 
         FIG. 425  is a diagram illustrating an example of next operation of a receiver in a store search situation in Embodiment 16. 
         FIG. 426  is a diagram illustrating an example of operation of a receiver in a movie advertisement situation in Embodiment 16. 
         FIG. 427  is a diagram illustrating an example of next operation of a receiver in a movie advertisement situation in Embodiment 16. 
         FIG. 428  is a diagram illustrating an example of next operation of a receiver in a movie advertisement situation in Embodiment 16. 
         FIG. 429  is a diagram illustrating an example of next operation of a receiver in a movie advertisement situation in Embodiment 16. 
         FIG. 430  is a diagram illustrating an example of operation of a receiver in a museum situation in Embodiment 16. 
         FIG. 431  is a diagram illustrating an example of next operation of a receiver in a museum situation in Embodiment 16. 
         FIG. 432  is a diagram illustrating an example of next operation of a receiver in a museum situation in Embodiment 16. 
         FIG. 433  is a diagram illustrating an example of next operation of a receiver in a museum situation in Embodiment 16. 
         FIG. 434  is a diagram illustrating an example of next operation of a receiver in a museum situation in Embodiment 16. 
         FIG. 435  is a diagram illustrating an example of next operation of a receiver in a museum situation in Embodiment 16. 
         FIG. 436  is a diagram illustrating an example of operation of a receiver in a bus stop situation in Embodiment 16. 
         FIG. 437  is a diagram illustrating an example of next operation of a receiver in a bus stop situation in Embodiment 16. 
         FIG. 438  is a diagram for describing imaging in Embodiment 16. 
         FIG. 439  is a diagram for describing transmission and imaging in Embodiment 16. 
         FIG. 440  is a diagram for describing transmission in Embodiment 16. 
         FIG. 441  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 442  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 443  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 444  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 445  is a diagram illustrating an example of operation of a receiver in Embodiment 17. 
         FIG. 446  is a diagram illustrating an example of operation of a receiver in Embodiment 17. 
         FIG. 447  is a diagram illustrating an example of operation of a system including a transmitter, a receiver, and a server in Embodiment 17. 
         FIG. 448  is a block diagram illustrating a structure of a transmitter in Embodiment 17. 
         FIG. 449  is a block diagram illustrating a structure of a receiver in Embodiment 17. 
         FIG. 450  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 451  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 452  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 453  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 454  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 455  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 456  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
         FIG. 457  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 458  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 459  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 460  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 461  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 462  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 463  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 464  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 465  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 466  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 467  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 468  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 469  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 470  is a diagram illustrating a coding scheme in Embodiment 17. 
         FIG. 471  is a diagram illustrating a coding scheme that can receive light even in the case of capturing an image in an oblique direction in Embodiment 17. 
         FIG. 472  is a diagram illustrating a coding scheme that differs in information amount depending on distance in Embodiment 17. 
         FIG. 473  is a diagram illustrating a coding scheme that differs in information amount depending on distance in Embodiment 17. 
         FIG. 474  is a diagram illustrating a coding scheme that divides data in Embodiment 17. 
         FIG. 475  is a diagram illustrating an opposite-phase image insertion effect in Embodiment 17. 
         FIG. 476  is a diagram illustrating an opposite-phase image insertion effect in Embodiment 17. 
         FIG. 477  is a diagram illustrating a superresolution process in Embodiment 17. 
         FIG. 478  is a diagram illustrating a display indicating visible light communication capability in Embodiment 17. 
         FIG. 479  is a diagram illustrating information obtainment using a visible light communication signal in Embodiment 17. 
         FIG. 480  is a diagram illustrating a data format in Embodiment 17. 
         FIG. 481  is a diagram illustrating reception by estimating a stereoscopic shape in Embodiment 17. 
         FIG. 482  is a diagram illustrating reception by estimating a stereoscopic shape in Embodiment 17. 
         FIG. 483  is a diagram illustrating stereoscopic projection in Embodiment 17. 
         FIG. 484  is a diagram illustrating stereoscopic projection in Embodiment 17. 
         FIG. 485  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 486  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
         FIG. 487  is a diagram illustrating an example of a transmission signal in Embodiment 18. 
         FIG. 488  is a diagram illustrating an example of a transmission signal in Embodiment 18. 
         FIG. 489A  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 489B  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 489C  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 490A  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 490B  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 491A  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 491B  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 491C  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 492  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
         FIG. 493  is a diagram illustrating an example of a transmission signal in Embodiment 18. 
         FIG. 494  is a diagram illustrating an example of operation of a receiver in Embodiment 18. 
         FIG. 495  is a diagram illustrating an example of an instruction to a user displayed on a screen of a receiver in Embodiment 18. 
         FIG. 496  is a diagram illustrating an example of an instruction to a user displayed on a screen of a receiver in Embodiment 18. 
         FIG. 497  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
         FIG. 498  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
         FIG. 499  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
         FIG. 500  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
         FIG. 501  is a diagram for describing a use case in Embodiment 18. 
         FIG. 502  is a diagram illustrating an information table transmitted from a smartphone to a server in Embodiment 18. 
         FIG. 503  is a block diagram of a server in Embodiment 18. 
         FIG. 504  is a flowchart illustrating an overall process of a system in Embodiment 18. 
         FIG. 505  is a diagram illustrating an information table transmitted from a server to a smartphone in Embodiment 18. 
         FIG. 506  is a diagram illustrating flow of screen displayed on a wearable device from when a user receives information from a server in front of a store to when the user actually buys a product in Embodiment 18. 
         FIG. 507  is a diagram for describing another use case in Embodiment 18. 
         FIG. 508  is a diagram illustrating a service provision system using the reception method described in any of the foregoing embodiments. 
         FIG. 509  is a flowchart illustrating flow of service provision. 
         FIG. 510  is a flowchart illustrating service provision in another example. 
         FIG. 511  is a flowchart illustrating service provision in another example. 
         FIG. 512  is a diagram for describing a modulation scheme that facilitates reception in Embodiment 20. 
         FIG. 513  is a diagram for describing a modulation scheme that facilitates reception in Embodiment 20. 
         FIG. 514  is a diagram for describing communication using bright lines and image recognition in Embodiment 20. 
         FIG. 515  is a diagram for describing an imaging element use method suitable for visible light signal reception in Embodiment 20. 
         FIG. 516  is a diagram illustrating a captured image size suitable for visible light signal reception in Embodiment 20. 
         FIG. 517  is a diagram illustrating a captured image size suitable for visible light signal reception in Embodiment 20. 
         FIG. 518  is a diagram for describing visible light signal reception using zoom in Embodiment 20. 
         FIG. 519  is a diagram for describing an image data size reduction method suitable for visible light signal reception in Embodiment 20. 
         FIG. 520  is a diagram for describing a modulation scheme with high reception error detection accuracy in Embodiment 20. 
         FIG. 521  is a diagram for describing a change of operation of a receiver according to situation in Embodiment 20. 
         FIG. 522  is a diagram for describing notification of visible light communication to humans in Embodiment 20. 
         FIG. 523  is a diagram for describing expansion in reception range by a diffusion plate in Embodiment 20. 
         FIG. 524  is a diagram for describing a method of synchronizing signal transmission from a plurality of projectors in Embodiment 20. 
         FIG. 525  is a diagram for describing a method of synchronizing signal transmission from a plurality of displays in Embodiment 20. 
         FIG. 526  is a diagram for describing visible light signal reception by an illuminance sensor and an image sensor in Embodiment 20. 
         FIG. 527  is a diagram for describing a reception start trigger in Embodiment 20. 
         FIG. 528  is a diagram for describing a reception start gesture in Embodiment 20. 
         FIG. 529  is a diagram for describing an example of application to a car navigation system in Embodiment 20. 
         FIG. 530  is a diagram for describing an example of application to a car navigation system in Embodiment 20. 
         FIG. 531  is a diagram for describing an example of application to content protection in Embodiment 20. 
         FIG. 532  is a diagram for describing an example of application to an electronic lock in Embodiment 20. 
         FIG. 533  is a diagram for describing an example of application to store visit information transmission in Embodiment 20. 
         FIG. 534  is a diagram for describing an example of application to location-dependent order control in Embodiment 20. 
         FIG. 535  is a diagram for describing an example of application to route guidance in Embodiment 20. 
         FIG. 536  is a diagram for describing an example of application to location notification in Embodiment 20. 
         FIG. 537  is a diagram for describing an example of application to use log storage and analysis in Embodiment 20. 
         FIG. 538  is a diagram for describing an example of application to screen sharing in Embodiment 20. 
         FIG. 539  is a diagram for describing an example of application to screen sharing in Embodiment 20. 
         FIG. 540  is a diagram for describing an example of application to position estimation using a wireless access point in Embodiment 20. 
         FIG. 541  is a diagram illustrating a structure of performing position estimation by visible light communication and wireless communication in Embodiment 20. 
         FIG. 542A  is a flowchart of an information communication method according to an aspect of the present disclosure. 
         FIG. 542B  is a block diagram of an information communication device according to an aspect of the present disclosure. 
         FIG. 543  is a diagram illustrating a watch including light sensors. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An information communication method according to an aspect of the present disclosure is an information communication method of obtaining information from a subject, the information communication method including: setting a first exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a plurality of bright lines corresponding to a plurality of exposure lines included in the image sensor appear according to a change in luminance of the subject; obtaining a bright line image including the plurality of bright lines, by capturing the subject changing in luminance by the image sensor with the set first exposure time; and obtaining the information by demodulating data specified by a pattern of the plurality of bright lines included in the obtained bright line image, wherein in the obtaining of a bright line image, exposure starts sequentially for the plurality of exposure lines each at a different time, and exposure of each of the plurality of exposure lines starts after a predetermined blank time elapses from when exposure of an adjacent exposure line adjacent to the exposure line ends. 
     In this way, the exposure of each of the plurality of exposure lines starts a predetermined blank time after the exposure of the adjacent exposure line adjacent to the exposure line ends, for instance as illustrated in  FIG. 24D  described later. This eases the recognition of the change in luminance of the subject. As a result, the information can be appropriately obtained from the subject. 
     For example, in the obtaining of a bright line image, each of the plurality of exposure lines may not overlap in exposure time the adjacent exposure line, and the predetermined blank time may be provided between the exposure of each of the plurality of exposure lines and the exposure of the adjacent exposure line. 
     For example, the information communication method may further include: setting a second exposure time of the image sensor so that exposure starts sequentially for the plurality of exposure lines in the image sensor each at a different time and each of the plurality of exposure lines partially overlaps in exposure time the adjacent exposure line; and obtaining a normal image by capturing the subject with the second exposure time, wherein in the obtaining of a bright line image, the first exposure time is shorter than the second exposure time and is less than or equal to 1/480 second so that the plurality of bright lines appear in the bright line image. 
     For example, a same reading method may be used to read data from the image sensor in the obtaining of a bright line image and in the obtaining of a normal image. 
     For example, the first exposure time of each of the plurality of exposure lines may be shorter than a shortest one of light emission times during each of which the subject changing in luminance maintains a predetermined luminance value. 
     For example, the first exposure time of each of the plurality of exposure lines may be longer than a transition time during which the subject changes in luminance from a maximum value to a minimum value. 
     For example, the first exposure time of each of the plurality of exposure lines may be longer than one cycle of high frequency noise in the change in luminance of the subject. 
     These general and specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of systems, methods, integrated circuits, computer programs, or computer-readable recording media. 
     Hereinafter, embodiments are specifically described with reference to the Drawings. 
     Each of the embodiments described below shows a general or specific example. The numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, steps, the processing order of the steps etc. shown in the following embodiments are mere examples, and therefore do not limit the scope of the present disclosure. Therefore, among the structural elements in the following embodiments, structural elements not recited in any one of the independent claims representing the broadest concepts are described as arbitrary structural elements. 
     Embodiment 1 
     (Signal transmission by phase modulation)  FIG. 1  is a timing diagram of a transmission signal in an information communication device in Embodiment 1. 
     In  FIG. 1 , a reference waveform (a) is a clock signal of period T, which serves as the reference for the timing of the transmission signal. A transmission symbol (b) represents a symbol string generated based on a data string to be transmitted. Here, the case of one bit per symbol is illustrated as an example, which is the same binary as the transmission data. A transmission waveform (c) is a transmission waveform phase-modulated according to the transmission symbol with respect to the reference waveform. The transmission light source is driven according to this waveform. The phase modulation is performed by phase-shifting the reference waveform in correspondence with the symbol. In this example, symbol 0 is assigned phase 0°, and symbol 1 is assigned phase 180°. 
       FIG. 2  is a diagram illustrating the relations between the transmission signal and the reception signal in Embodiment 1. 
     The transmission signal is the same as in  FIG. 1 . The light source emits light only when the transmission signal is 1, with the light emission time being indicated by the diagonally right down shaded area. The diagonally right up shaded band represents the time during which the pixels of the image sensor are exposed (exposure time tE). The signal charge of the pixels of the image sensor is generated in the area overlapping with the diagonally right down shaded area indicating the light emission time. A pixel value p is proportional to the overlapping area. Here, the relation of Expression 1 holds between the exposure time tE and the period T.
 
 tE=T/ 2×(2 n+ 1) (where  n  is a natural number)   (Expression 1).
 
     Note that  FIGS. 2 to 6  illustrate the case where n=2, that is, tE=2.5 T. 
     The reception waveform indicates the pixel value p of each line. Here, the value of the pixel value axis is normalized with the intensity of received light per period being set as 1. As mentioned above, the exposure time tE has the section of T(n+½), so that the pixel value p is always in the range of n≤p≤n+1. In the example in  FIG. 2 , 2≤p≤3. 
       FIGS. 3 to 5  are each a diagram illustrating the relations between the transmission signal and the reception signal for a symbol string different from that in  FIG. 2 . 
     The transmission signal has a preamble including a consecutive same-symbol string (e.g. string of consecutive symbols 0) (not illustrated). The receiver generates the reference (fundamental) signal for reception from the consecutive symbol string in the preamble, and uses it as the timing signal for reading the symbol string from the reception waveform. In detail, for consecutive symbols 0, the reception waveform returns a fixed waveform repeating 2→3→2, and the clock signal is generated as the reference signal based on the output timing of the pixel value 3, as illustrated in  FIG. 2 . 
     Next, the symbol reading from the reception waveform can be performed in such a manner that the reception signal in one section of the reference signal is read where the pixel value 3 is read as symbol 0 and the pixel value 2 is read as symbol 1.  FIGS. 3 to 5  illustrate the state of reading symbols in the fourth period. 
       FIG. 6  is a diagram summarizing  FIGS. 2 to 5 . Since the lines are closely aligned, the pixel boundary in the line direction is omitted so that the pixels are continuous in the drawing. The state of reading symbols in the fourth to eighth periods is illustrated here. 
     According to such a structure, in this embodiment, the average of the intensity of the light signal taken for a sufficiently longer time than the period of the reference wave is always constant. By setting the frequency of the reference wave appropriately high, it is possible to set the time to be shorter than the time in which humans perceive a change in light intensity. Hence, the transmission light emitting source observed by the human eye appears to be emitting light uniformly. Since no flicker of the light source is perceived, there is an advantageous effect of causing no annoyance on the user as in the previous embodiment. 
     In a situation where the exposure time of each line is long and the time overlapping with the exposure time of the adjacent line is long, the amplitude modulation (ON/OFF modulation) in the previous embodiment has the problem that the signal frequency (symbol rate) cannot be increased and so the sufficient signal transmission speed cannot be attained. In this embodiment, on the other hand, the signal leading and trailing edges are detectable even in such a situation, with it being possible to increase the signal frequency and attain the high signal transmission speed. 
     The term “phase modulation” used here means the phase modulation for the reference signal waveform. In the original sense, a carrier is light, which is amplitude-modulated (ON/OFF modulated) and transmitted. Therefore, the modulation scheme in this signal transmission is one type of amplitude modulation. 
     Note that the transmission signal mentioned above is merely an example, and the number of bits per symbol may be set to 2 or more. Besides, the correspondence between the symbol and the phase shift is not limited to 0° and 180°, and an offset may be provided. 
     Though not mentioned above, the structures and operations of the light signal generating means and light signal receiving means described later in Embodiments 6 to 11 with reference to  FIGS. 124 to 200  may be replaced with the structures and operations of the high-speed light emitting means and light signal receiving means described in Embodiment 3 and its subsequent embodiments with reference to  FIG. 21  onward, to achieve the same advantageous effects. Conversely, the high-speed light emitting means and receiving means in Embodiment 3 and its subsequent embodiments may equally be replaced with the low-speed light emitting means and receiving means. 
     For instance, in the above-mentioned example where the data such as position information in the light signal from the lighting is received using the face camera which is the display-side camera of the mobile phone in  FIG. 17  or using the opposite in camera in  FIG. 16 , the up/down direction can be detected based on gravity through the use of the 9-axis sensor. 
     Consider the case of receiving the light signal by the mobile phone placed on the table in the restaurant, as illustrated in  FIG. 19 . The light signal may be received by operating the face camera when the front side of the mobile phone is facing upward, and operating the in camera when the front side is facing downward, according to the signal of the 9-axis sensor. This contributes to lower power consumption and faster light signal reception, as unnecessary camera operations can be stopped. The same operation may be performed by detecting the orientation of the camera on the table from the brightness of the camera. Moreover, when the camera switches from the imaging mode to the light signal reception mode, a shutter speed increase command and an imaging element sensitivity increase command may be issued to the imaging circuit unit. This has an advantageous effect of enhancing the sensitivity and making the image brighter. Though noise increases with the increase in sensitivity, such noise is white noise. Since the light signal is in a specific frequency band, the detection sensitivity can be enhanced by separation or removal using a frequency filter. This enables detection of a light signal from a dark lighting device. 
     In the present disclosure, a lighting device in a space which is mainly indoors is caused to emit a light signal, and a camera unit of a mobile terminal including a communication unit, a microphone, a speaker, a display unit, and the camera unit with the in camera and the face camera receives the light signal to obtain position information and the like. When the mobile terminal is moved from indoors to outdoors, the position information can be detected by GPS using satellite. Accordingly, by obtaining the position information of the boundary of the light signal area and automatically switching to the signal reception from GPS, an advantageous effect of seamless position detection can be achieved. 
     When moving from outdoors to indoors, the boundary is detected based on the position information of GPS or the like, to automatically switch to the position information of the light signal. In the case where barcode is displayed on the display unit of the mobile phone for authentication by a POS terminal at an airplane boarding gate or a store, the use of a server causes a long response time and is not practical, and therefore only one-way authentication is possible. 
     According to the present disclosure, on the other hand, mutual authentication can be carried out by transmitting the light signal from the light emitting unit of the reader of the POS terminal or the like to the face camera unit of the mobile phone. This contributes to enhanced security. 
     Embodiment 2 
       FIG. 7  is a diagram illustrating a principle in Embodiment 2.  FIGS. 8 to 20  are each a diagram illustrating an example of operation in Embodiment 2. 
     An image sensor illustrated in (a) in  FIG. 7  has a delay in exposure time of each line  1 . At a normal shutter speed, the lines have temporally overlapping parts, and so the light signal of the same time is mixed in each line and cannot be identified. When decreasing the shutter open time, no overlap occurs as in (a) in  FIG. 7  if the exposure time is reduced to less than or equal to a predetermined shutter speed, as a result of which the light signal can be temporally separated and read on a line basis. 
     When the light signal “1011011” as in the upper part of (a) in  FIG. 7  is given in this state, the first light signal “1” enters in the shutter open time of line  1  and so is photoelectrically converted in line  1 , and output as “1” of an electrical signal  2   a  in (b) in  FIG. 7 . Likewise, the next light signal “0” is output as the electrical signal “0” in (b). Thus, the 7-bit light signal “1011011” is accurately converted to the electrical signal. 
     In actuality, there is a dead time due to a vertical blanking time as in (b) in  FIG. 7 , so that the light signal in some time slot cannot be extracted. In this embodiment, this blanking time problem is solved by changing, when switching from “normal imaging mode” to “light signal reading mode”, the access address of the imaging device such as CMOS to read the first read line  1   a  following the last read line  1   h  at the bottom. Though this has a slight adverse effect on the image quality, an advantageous effect of capable of continuous (seamless) reading can be achieved, which contributes to significantly improved transmission efficiency. 
     In this embodiment, one symbol at the maximum can be assigned to one line. In the case of employing the below-mentioned synchronization method, transmission of 30 kbps at the maximum is theoretically possible when using an imaging element of 30 fps and 1000 lines. 
     Note that synchronization can be established by, with reference to the signal of the light receiving element of the camera as in  FIG. 8 , vertically changing the line access clock so as to attain the maximum contrast or reduce the data error rate. In the case where the line clock of the image sensor is faster than the light signal, synchronization can be established by receiving one symbol of the light signal in n lines which are 2 or 3 lines as in  FIG. 8 . 
     Moreover, when a display of a TV in  FIG. 9  or a TV in the left part of  FIG. 10  or a light source vertically divided into n which is 10 as an example is captured by the camera of the mobile phone by switching to the detection mode of non-blanking, high-speed electronic shutter, and the like according to the present disclosure, ten stripe patterns specific to this embodiment can be detected independently of each other as in the right part of  FIG. 10 . Thus, a 10-times (n-times) transfer rate can be achieved. 
     For example, dividing an image sensor of 30 fps and 1000 lines into 10 results in 300 kbps. In HD video, there are 1980 pixels in the horizontal direction, so that the division into 50 is possible. This yields 1.5 Mbps, enabling reception of video data. If the number is 200, HD video can be transmitted. 
     To achieve the advantageous effects in this embodiment, it is necessary to decrease the shutter time to less than or equal to T 0  where T 0  is the detectable longest exposure time. As in the upper right part of  FIG. 7 , the shutter time needs to be less than or equal to half of 1/fp where fp is the frame frequency, for the following reason. Blanking during imaging is half of one frame at the maximum. That is, the blanking time is less than or equal to half of the imaging time. The actual imaging time is therefore ½fp at the shortest. 
     However, 4-value PPM or the like is necessary to suppress flicker, so that the shutter time is less than or equal to 1/1(fp×2×4), i.e. ⅛fp. Since the camera of the mobile phone typically has fp=30, 60, by setting the shutter speed less than or equal to 1/240, 1/480, i.e. the shutter speed less than or equal to 1/480, visible light communication according to this embodiment can be received using the camera of the mobile phone or the like while maintaining compatibility. 
     There are actually a large number of mobile phones that do not employ the synchronization method according to this embodiment, and so asynchronous communication is initially performed. In this case, by receiving one symbol using scan lines greater than or equal to 2 times the clock of the light signal, in more detail, 2 to 10 times the clock of the light signal, compatible communication can be realized though with a decrease in information rate. 
     In the case of a lighting device in which flicker needs to be suppressed, light emission is performed by turning OFF or reducing light during one time slot of 4-value PPM, i.e. one time slot of four bits. In this case, though the bitrate decreases by half, flicker is eliminated. Accordingly, the device can be used as a lighting device and transmit light and data. 
       FIG. 11  illustrates a situation of light signal reception in a state where all lightings indoors transmit a common signal during a common time slot and an individual lighting L 4  transmits individual sub-information-during an individual time slot. L 4  has a small area, and so takes time to transmit a large amount of data. Hence, only an ID of several bits is transmitted during the individual time slot, while all of L 1 , L 2 , L 3 , L 4 , and L 5  transmit the same common information during the common time slot. 
     This is described in detail, with reference to  FIG. 12A . In time slot A in the lower part of  FIG. 12A , two lightings in a main area M which are all lightings in a room and S 1 , S 2 , S 3 , and S 4  at parts of the lightings transmit the same light signal simultaneously, to transmit common information “room reference position information, arrangement information of individual device of each ID (difference position information from reference position), server URL, data broadcasting, LAN transmission data”. Since the whole room is illuminated with the same light signal, there is an advantageous effect that the camera unit of the mobile phone can reliably receive data during the common time slot. 
     In time slot B, on the other hand, the main area M does not blink but continuously emits light with 1/n of the normal light intensity, as illustrated in the upper right part of  FIG. 12A . In the case of 4-value PPM, the average light intensity is unchanged when emitting light with ¾, i.e. 75%, of the normal light intensity, as a result of which flicker can be prevented. Blinking in the range where the average light intensity is unchanged causes no flicker, but is not preferable because noise occurs in the reception of the partial areas S 1 , S 2 , S 3 , and S 4  in time slot B. In time slot B, S 1 , S 2 , S 3 , and S 4  each transmit a light signal of different data. The main area M does not transmit a modulated signal, and so is separated in position as in the screen of the mobile phone in the upper right part of  FIG. 12A . Therefore, for example in the case of extracting the image of the area S 1 , stripes appearing in the area can be easily detected because there is little noise, with it being possible to obtain data stably. 
       FIG. 12B  is a diagram for describing operation of a transmitter and a receiver in this embodiment. 
     A transmitter  8161  such as a signage changes luminance of an area A showing “A shop” and an area B showing “B shop”. As a result, signals A and B are transmitted from the respective areas. For example, each of the signals A and B includes a common part indicating common information and an individual part indicating different information. The common parts of the signals A and B are transmitted simultaneously. Having received at least one of the common parts of the signals A and B, a receiver  8162  displays an image of the entire signage. The transmitter may transmit the individual parts of the signals A and B simultaneously or at different times. For example, having received the individual part of the signal B, the receiver  8162  displays detailed shop information or the like corresponding to the area B. 
       FIG. 12C  is a diagram for describing operation of a transmitter and a receiver in this embodiment. 
     For example, the transmitter  8161  transmits the common parts of the signals A and B simultaneously as mentioned above, and then transmits the individual parts of the signals A and B indicating different information simultaneously. The receiver  8162  receives the signals from the transmitter  8161 , by capturing the transmitter  8161 . 
     When the transmitter  8161  is transmitting the common parts of the signals A and B, the transmitter  8161  can be captured as one large area without being divided into two areas. The receiver  8162  can accordingly receive the common part, even when situated far from the transmitter  8161 . The receiver  8162  then obtains information associated with the common part from a server, and displays the information. For instance, the server transmits information of all shops shown on the signage which is the transmitter  8161 , to the receiver  8162 . Alternatively, the server selects information of an arbitrary shop from the shops, and transmits the selected information to the receiver  8162 . The server transmits, for example, information of a shop that pays the largest registration fee of all shops, to the receiver  8162 . As an alternative, the server transmits information of a shop corresponding to an area (area A or B) at the center of the range captured by the camera of the receiver  8162 . As another alternative, the server randomly selects a shop, and transmits information of the shop to the receiver  8162 . 
     In the case where the receiver  8162  is situated near the transmitter  8161 , the receiver  8162  can receive the individual part of the signal A or B. The receiver  8162  then obtains information associated with the individual part, from the server. 
     For instance, in the case of 4-value PPM, when the camera scans in the lateral direction (horizontal direction) as illustrated in  FIG. 13 , a lighting L 2  is captured by a face camera, and “0101”, i.e. 4-bit data per frame, can be demodulated as a result of three stripes appearing as illustrated on the right side. ID data is included in this data. Accordingly, there is an advantageous effect that the position of the mobile terminal can be detected at high speed, i.e. in a short time, by computing the distance difference information between the reference position information of the common data and each ID of the individual data or the arrangement information of each ID of the individual data. Thus, for example, the data and positions of four light sources can be instantaneously recognized in one frame information, merely by transmitting 2-bit ID information. 
     An example of using low-bit ID information of individual light sources is described below, with reference to  FIG. 14 . 
     In this embodiment, in common data  101  in  FIG. 14 , a large amount of data including a reference position, a server URL, arrangement information of each ID, and area-specific data broadcasting are transmitted in a common time slot using all lightings as illustrated. 
     Individual IDs of L 1 , L 2 , L 3 , and L 4  to L 8  in (a) in  FIG. 14  can be 3-bit demodulated as mentioned earlier. 
     As illustrated in (b) in  FIG. 14 , by transmitting signals of a frequency f 1  and a frequency f 2 , too, one or more stripes that are specific to the present disclosure are detected in each lighting unit and converted to ID data corresponding to the frequency or ID data corresponding to the modulated data. Computing this pattern using the arrangement information makes it possible to recognize from which position the image is captured. That is, the position of the terminal can be specified as the arrangement information of each ID and the reference position information can be obtained from L 0 . 
     In (b) in  FIG. 14 , by assigning the frequencies f 1  and f 2  to IDs and setting, for example, f 1 =1000 Hz, f 2 =1100 Hz, . . . , f 16 =2500 Hz, a hexadecimal value, i.e. a 4-bit value, can be expressed by the frequency. Changing the transmission frequency at predetermined time intervals enables more signals to be transmitted. When changing the frequency or starting/ending the modulation, the average luminance is kept constant before and after the change. This has an advantageous effect of causing no flicker perceivable by the human eye. 
     Note that, since the receiver detects frequencies from signal periods, reception errors can be reduced by assigning signals so that the inverses or logarithms of frequencies are at regular intervals, rather than by assigning frequencies to signals at regular intervals. 
     For example, changing the signal per 1/15 second enables transmission of 60 bits per second. A typical imaging device captures 30 frames per second. Accordingly, by transmitting the signal at the same frequency for 1/15 second, the transmitter can be reliably captured even if the transmitter is shown only in one part of the captured image. 
     Moreover, by transmitting the signal at the same frequency for 1/15 second, the signal can be received even in the case where the receiver is under high load and unable to process some frame or in the case where the imaging device is capable of capturing only 15 frames per second. 
     When frequency analysis is conducted by, for example, Fourier transforming the luminance in the direction perpendicular to the exposure lines, the frequency of the transmission signal appears as a peak. In the case where a plurality of frequencies, as in a frequency change part, are captured in one frame, a plurality of peaks weaker than in the case of Fourier transforming the single frequency signal are obtained. The frequency change part may be provided with a protection part so as to prevent adjacent frequencies from being mixed with each other. 
     According to this method, the transmission frequency can be analyzed even in the case where light transmitted at a plurality of frequencies in sequence is captured in one frame, and the transmission signal can be received even when the frequency of the transmission signal is changed at time intervals shorter than 1/15 second or 1/30 second. 
     The transmission signal sequence can be recognized by performing Fourier transform in a range shorter than one frame. Alternatively, captured frames may be concatenated to perform Fourier transform in a range longer than one frame. In this case, the luminance in the blanking time in imaging is treated as unknown. The protection part is a signal of a specific frequency, or is unchanged in luminance (frequency of 0 Hz). 
     In (b) in  FIG. 14 , the FM modulated signal of the frequency f 2  is transmitted and then the PPM modulated signal is transmitted. As a result of alternately transmitting the FM modulated signal and the PPM modulated signal in this way, even a receiver that supports only one of the methods can receive the information. Besides, more important information can be transmitted with higher priority, by assigning the more important information to the FM modulated signal which is relatively easy to receive. 
     In this embodiment, since the ID of each device and its position on the screen are simultaneously obtained, it is possible to download image information, position information, and an application program linked with each ID of the lighting in a database of a cloud server at an URL linked with the lighting, and superimpose and display an image of a related product or the like on the video of the device having the lighting of the ID according to AR. In such a case, switching the demodulation mode to the imaging mode in this embodiment produces an advantageous effect that an AR image superimposed on beautiful video can be attained. 
     As illustrated in  FIG. 11 , by transmitting distance difference d in east, west, south, and north between the light source of each ID and the reference position in time slot A, the accurate position of the lighting L 4  in cm is known. Next, height h is calculated from ceiling height H and the height of the user of the mobile phone, and the orientation information of the mobile phone is corrected using a 9-axis sensor, to obtain accurate camera direction angle θ 2  and angle θ 1  between the lighting and the mobile phone. d is calculated according to, for example, d=(H−h)×arctan·θ 1 . 
     The position of the mobile phone can be calculated with high accuracy in this way. By transmitting the common light signal in time slot A and the individual light signal in time slot B, an advantageous effect of ensuring that the large amount of common information and the small amount of individual information such as IDs are substantially simultaneously transmitted can be achieved. 
     The individual light sources S 1  to S 4  are captured as in the mobile terminal in the upper light part of  FIG. 12A . As illustrated in the time chart in the lower part of  FIG. 12A , only S 1  transmits the light signal in time C. There is an advantageous effect that the detection can be made without influence of noise, because only one stripe appears as in t=C in  FIG. 15 . 
     Two pieces of individual data may be transmitted as in t=D, E. Transmitting most spatially separate individual data as in t=H, I has an advantageous effect of a reduction in error rate because they are easily separated on the screen. 
     In t=C in  FIG. 15 , only S 1  needs to be demodulated, and accordingly the scan of the image sensor for the other areas is unnecessary. Hence, by reducing the number of scan lines so as to include the area of S 1  as in t=C, it is possible to scan only the area of S 1  and demodulate the data. This has an advantageous effect that not only a speedup can be achieved but also a large amount of data can be demodulated only in the narrow area of S 1 . 
     In such a case, however, there is a possibility that the area S 1  deviates from the scan range of the image sensor due to hand movement. 
     Hence, image stabilization as illustrated in  FIG. 16  is important. The gyroscope included in the mobile phone is typically unable to detect fine rotation in a narrow range such as hand movement. 
     Accordingly, in the case of receiving the light signal of L 2  by the face camera as in the left part of  FIG. 16 , it is difficult to detect blur due to hand movement from the image captured by the face camera when, for example, the scan is limited. In view of this, the in camera is turned ON, and blur is detected from the image of the in camera to correct the scan range or the detection range. Thus, the effect of hand movement can be reduced. This is because the hand movement of the face camera and the hand movement of the in camera are the same. 
     When the shutter speed of the scan area other than the light signal pattern in the face camera is decreased and the normal image is obtained from this area, image stabilization can be performed using this image. In this case, blur detection and signal detection are possible with one camera. The same advantageous effect can be achieved in the case of using the in camera in the right part of  FIG. 16 . 
     In  FIG. 17 , the light signal is detected by the face camera to first obtain the position information of the terminal. 
     In the case of calculating the moving distance I 2  from this point, the 9-axis sensor for the mobile phone is not useful because of poor accuracy. In such a case, the moving distance I 2  can be calculated from the orientation of the terminal and the change in the pattern of the floor surface using the in camera opposite to the face camera, as in  FIG. 17 . The pattern of the ceiling may be detected using the face camera. 
     Actual example of applications are described below. 
       FIG. 18  is a diagram illustrating a situation of receiving data broadcasting which is common data from the ceiling lighting and obtaining the position of the user itself from individual data, inside a station. 
     In  FIG. 19 , after a mobile terminal on which barcode is displayed displays authentication information and a terminal of a coffee shop reads the authentication information, a light emitting unit in the terminal of the shop emits light and the mobile terminal receives the light according to the present disclosure to perform mutual authentication. The security can be enhanced in this way. The authentication may be performed in reverse order. 
     The customer carrying the mobile terminal sits at a table and transmits obtained position information to the terminal of the shop via a wireless LAN or the like, as a result of which the position of the customer is displayed on the shop staff&#39;s terminal. This enables the shop staff to bring the ordered drink to the table of the position information of the customer ordering the drink. 
     In  FIG. 20 , the passenger detects his or her position in a train or an airplane according to the method of this embodiment, and orders a product such as food through his/her terminal. The crew has a terminal according to the present disclosure on the cart and, since the ID number of the ordered product is displayed at the position of the customer on the screen, properly delivers the ordered product of the ID to the customer. 
       FIG. 10  is a diagram illustrating the case of using the method or device of this embodiment for a backlight of a display of a TV or the like. Since a fluorescent lamp, an LED, or an organic EL device is capable of low luminance modulation, transmission can be performed according to this embodiment. In terms of characteristics, however, the scan direction is important. In the case of portrait orientation as in a smartphone, the scan is horizontally performed. Hence, by providing a horizontally long light emitting area at the bottom of the screen and reducing the contrast of video of the TV or the like to be closer to white, there is an advantageous effect that the signal can be received easily. 
     In the case of scanning in the vertical direction as in a digital camera, a vertically long display is provided as in the right side of the screen in  FIG. 9 . 
     By providing these two areas in one screen and emitting the same light signal from both areas, the signal can be received by an image sensor of either scan direction. 
     In the case where a horizontal scan image sensor is receiving light of a vertical light emitting unit, a message such as “please rotate to horizontal” may be displayed on the terminal screen to prompt the user to receive the light more accurately and faster. 
     Note that the communication speed can be significantly increased by controlling the scan line read clock of the image sensor of the camera to synchronize with the light emission pattern of the light emitting unit as in  FIG. 8 . 
     In the case of detecting one symbol of the light emission pattern in 2 lines as in (a) in  FIG. 8 , synchronization is established in the pattern in the left part. In the pattern in the middle part, the image sensor reading is fast, so that the read clock of the imaging element is slowed down for synchronization. In the pattern in the right part, the read clock is speeded up for synchronization. 
     In the case of detecting one symbol in 3 lines as in (b) in  FIG. 8 , the read clock is slowed down in the pattern in the middle part, and speeded up in the pattern in the right part. 
     Thus, high speed optical communication can be realized. 
     In bidirectional communication, an infrared light receiving unit provided in the lighting device of the light emitting unit as a motion sensor may be used for reception, with it being possible to perform bidirectional reception in the lighting device with no additional component. The terminal may perform transmission using the electronic flash for the camera, or may be additionally provided with an inexpensive infrared light emitting unit. Thus, bidirectional communication is realized without significant component addition. 
     Embodiment 3 
     The following describes Embodiment 3. 
     (Observation of Luminance of Light Emitting Unit) 
     The following proposes an imaging method in which, when capturing one image, all imaging elements are not exposed simultaneously but the times of starting and ending the exposure differ between the imaging elements.  FIG. 21  illustrates an example of imaging where imaging elements arranged in a line are exposed simultaneously, with the exposure start time being shifted in order of lines. Here, the simultaneously exposed imaging elements are referred to as “exposure line”, and the line of pixels in the image corresponding to the imaging elements is referred to as “bright line”. 
     In the case of capturing a blinking light source shown on the entire imaging elements using this imaging method, bright lines (lines of brightness in pixel value) along exposure lines appear in the captured image as illustrated in  FIG. 22 . By recognizing this bright line pattern, the luminance change of the light source at a speed higher than the imaging frame rate can be estimated. Hence, transmitting a signal as the luminance change of the light source enables communication at a speed not less than the imaging frame rate. In the case where the light source takes two luminance values to express a signal, the lower luminance value is referred to as “low” (LO), and the higher luminance value is referred to as “high” (HI). The low may be a state in which the light source emits no light, or a state in which the light source emits weaker light than in the high. 
     By this method, information transmission is performed at a speed higher than the imaging frame rate. 
     In the case where the number of exposure lines whose exposure times do not overlap each other is 20 in one captured image and the imaging frame rate is 30 fps, it is possible to recognize a luminance change in a period of 1.67 millisecond. In the case where the number of exposure lines whose exposure times do not overlap each other is 1000, it is possible to recognize a luminance change in a period of 1/30000 second (about 33 microseconds). Note that the exposure time is set to less than 10 milliseconds, for example. 
       FIG. 22  illustrates a situation where, after the exposure of one exposure line ends, the exposure of the next exposure line starts. 
     In this situation, when transmitting information based on whether or not each exposure line receives at least a predetermined amount of light, information transmission at a speed of fl bits per second at the maximum can be realized where f is the number of frames per second (frame rate) and l is the number of exposure lines constituting one image. 
     Note that faster communication is possible in the case of performing time-difference exposure not on a line basis but on a pixel basis. 
     In such a case, when transmitting information based on whether or not each pixel receives at least a predetermined amount of light, the transmission speed is film bits per second at the maximum, where m is the number of pixels per exposure line. 
     If the exposure state of each exposure line caused by the light emission of the light emitting unit is recognizable in a plurality of levels as illustrated in  FIG. 23 , more information can be transmitted by controlling the light emission time of the light emitting unit in a shorter unit of time than the exposure time of each exposure line. 
     In the case where the exposure state is recognizable in Elv levels, information can be transmitted at a speed of flElv bits per second at the maximum. 
     Moreover, a fundamental period of transmission can be recognized by causing the light emitting unit to emit light with a timing slightly different from the timing of exposure of each exposure line. 
       FIG. 24A  illustrates a situation where, before the exposure of one exposure line ends, the exposure of the next exposure line starts. That is, the exposure times of adjacent exposure lines partially overlap each other. This structure has the feature (1): the number of samples in a predetermined time can be increased as compared with the case where, after the exposure of one exposure line ends, the exposure of the next exposure line starts. The increase of the number of samples in the predetermined time leads to more appropriate detection of the light signal emitted from the light transmitter which is the subject. In other words, the error rate when detecting the light signal can be reduced. The structure also has the feature (2): the exposure time of each exposure line can be increased as compared with the case where, after the exposure of one exposure line ends, the exposure of the next exposure line starts. Accordingly, even in the case where the subject is dark, a brighter image can be obtained, i.e. the S/N ratio can be improved. Here, the structure in which the exposure times of adjacent exposure lines partially overlap each other does not need to be applied to all exposure lines, and part of the exposure lines may not have the structure of partially overlapping in exposure time. By keeping-part of the exposure lines from partially overlapping in exposure time, the occurrence of an intermediate color caused by exposure time overlap is suppressed on the imaging screen, as a result of which bright lines can be detected more appropriately. 
     In this situation, the exposure time is calculated from the brightness of each exposure line, to recognize the light emission state of the light emitting unit. 
     Note that, in the case of determining the brightness of each exposure line in a binary fashion of whether or not the luminance is greater than or equal to a threshold, it is necessary for the light emitting unit to continue the state of emitting no light for at least the exposure time of each line, to enable the no light emission state to be recognized. 
       FIG. 24B  illustrates the influence of the difference in exposure time in the case where the exposure start time of each exposure line is the same. In  7500   a , the exposure end time of one exposure line and the exposure start time of the next exposure line are the same. In  7500   b , the exposure time is longer than that in  7500   a . The structure in which the exposure times of adjacent exposure lines partially overlap each other as in  7500   b  allows a longer exposure time to be used. That is, more light enters the imaging element, so that a brighter image can be obtained. In addition, since the imaging sensitivity for capturing an image of the same brightness can be reduced, an image with less noise can be obtained. Communication errors are prevented in this way. 
       FIG. 24C  illustrates the influence of the difference in exposure start time of each exposure line in the case where the exposure time is the same. In  7501   a , the exposure end time of one exposure line and the exposure start time of the next exposure line are the same. In  7501   b , the exposure of one exposure line ends after the exposure of the next exposure line starts. The structure in which the exposure times of adjacent exposure lines partially overlap each other as in  7501   b  allows more lines to be exposed per unit time. This increases the resolution, so that more information can be obtained. Since the sample interval (i.e. the difference in exposure start time) is shorter, the luminance change of the light source can be estimated more accurately, contributing to a lower error rate. Moreover, the luminance change of the light source in a shorter time can be recognized. By exposure time overlap, light source blinking shorter than the exposure time can be recognized using the difference of the amount of exposure between adjacent exposure lines. 
     As described with reference to  FIGS. 24B and 24C , in the structure in which each exposure line is sequentially exposed so that the exposure times of adjacent exposure lines partially overlap each other, the communication speed can be dramatically improved by using, for signal transmission, the bright line pattern generated by setting the exposure time shorter than in the normal imaging mode. Setting the exposure time in visible light communication to less than or equal to 1/480 second enables an appropriate bright line pattern to be generated. Here, it is necessary to set (exposure time)&lt;⅛×f, where f is the frame frequency. Blanking during imaging is half of one frame at the maximum. That is, the blanking time is less than or equal to half of the imaging time. The actual imaging time is therefore ½f at the shortest. Besides, since 4-value information needs to be received within the time of ½f, it is necessary to at least set the exposure time to less than 1/(2f×4). Given that the normal frame rate is less than or equal to 60 frames per second, by setting the exposure time to less than or equal to 1/480 second, an appropriate bright line pattern is generated in the image data and thus fast signal transmission is achieved. 
       FIG. 24D  illustrates the advantage of using a short exposure time in the case where each exposure line does not overlap in exposure time. In the case where the exposure time is long, even when the light source changes in luminance in a binary fashion as in  7502   a , an intermediate-color part tends to appear in the captured image as in  7502   e , making it difficult to recognize the luminance change of the light source. By providing a predetermined non-exposure blank time (predetermined wait time) t D2  from when the exposure of one exposure line ends to when the exposure of the next exposure line starts as in  7502   d , however, the luminance change of the light source can be recognized more easily. That is, a more appropriate bright line pattern can be detected as in  7502   f . The provision of the predetermined non-exposure blank time is possible by setting a shorter exposure time t E  than the time difference t D  between the exposure start times of the exposure lines, as in  7502   d . In the case where the exposure times of adjacent exposure lines partially overlap each other in the normal imaging mode, the exposure time is shortened from the normal imaging mode so as to provide the predetermined non-exposure blank time. In the case where the exposure end time of one exposure line and the exposure start time of the next exposure line are the same in the normal imaging mode, too, the exposure time is shortened so as to provide the predetermined non-exposure time. Alternatively, the predetermined non-exposure blank time (predetermined wait time) t D2  from when the exposure of one exposure line ends to when the exposure of the next exposure line starts may be provided by increasing the interval t D  between the exposure start times of the exposure lines, as in  7502   g . This structure allows a longer exposure time to be used, so that a brighter image can be captured. Moreover, a reduction in noise contributes to higher error tolerance. Meanwhile, this structure is disadvantageous in that the number of samples is small as in  7502   h , because fewer exposure lines can be exposed in a predetermined time. Accordingly, it is desirable to use these structures depending on circumstances. For example, the estimation error of the luminance change of the light source can be reduced by using the former structure in the case where the imaging object is bright and using the latter structure in the case where the imaging object is dark. 
     Here, the structure in which the exposure times of adjacent exposure lines partially overlap each other does not need to be applied to all exposure lines, and part of the exposure lines may not have the structure of partially overlapping in exposure time. Moreover, the structure in which the predetermined non-exposure blank time (predetermined wait time) is provided from when the exposure of one exposure line ends to when the exposure of the next exposure line starts does not need to be applied to all exposure lines, and part of the exposure lines may have the structure of partially overlapping in exposure time. This makes it possible to take advantage of each of the structures. Furthermore, the same reading method or circuit may be used to read a signal in the normal imaging mode in which imaging is performed at the normal frame rate (30 fps, 60 fps) and the visible light communication mode in which imaging is performed with the exposure time less than or equal to 1/480 second for visible light communication. The use of the same reading method or circuit to read a signal eliminates the need to employ separate circuits for the normal imaging mode and the visible light communication mode. The circuit size can be reduced in this way. 
       FIG. 24E  illustrates the relation between the minimum change time t S  of light source luminance, the exposure time t E , the time difference t D  between the exposure start times of the exposure lines, and the captured image. In the case where t E +t D &lt;t S , imaging is always performed in a state where the light source does not change from the start to end of the exposure of at least one exposure line. As a result, an image with clear luminance is obtained as in  7503   d , from which the luminance change of the light source is easily recognizable. In the case where 2t E &gt;t S , a bright line pattern different from the luminance change of the light source might be obtained, making it difficult to recognize the luminance change of the light source from the captured image. 
       FIG. 24F  illustrates the relation between the transition time t T  of light source luminance and the time difference t D  between the exposure start times of the exposure lines. When t D  is large as compared with t T , fewer exposure lines are in the intermediate color, which facilitates estimation of light source luminance. It is desirable that t D &gt;t T , because the number of exposure lines in the intermediate color is two or less consecutively. Since t T  is less than or equal to 1 microsecond in the case where the light source is an LED and about 5 microseconds in the case where the light source is an organic EL device, setting t D  to greater than or equal to 5 microseconds facilitates estimation of light source luminance. 
       FIG. 24G  illustrates the relation between the high frequency noise t HT  of light source luminance and the exposure time t E . When t E  is large as compared with t HT , the captured image is less influenced by high frequency noise, which facilitates estimation of light source luminance. When t E  is an integral multiple of t HT , there is no influence of high frequency noise, and estimation of light source luminance is easiest. For estimation of light source luminance, it is desirable that t E &gt;t HT . High frequency noise is mainly caused by a switching power supply circuit. Since t HT  is less than or equal to 20 microseconds in many switching power supplies for lightings, setting t E  to greater than or equal to 20 microseconds facilitates estimation of light source luminance. 
       FIG. 24H  is a graph representing the relation between the exposure time t E  and the magnitude of high frequency noise when t HT  is 20 microseconds. Given that t HT  varies depending on the light source, the graph demonstrates that it is efficient to set t E  to greater than or equal to 15 microseconds, greater than or equal to 35 microseconds, greater than or equal to 54 microseconds, or greater than or equal to 74 microseconds, each of which is a value equal to the value when the amount of noise is at the maximum. Though t E  is desirably larger in terms of high frequency noise reduction, there is also the above-mentioned property that, when t E  is smaller, an intermediate-color part is less likely to occur and estimation of light source luminance is easier. Therefore, t E  may be set to greater than or equal to 15 microseconds when the light source luminance change period is 15 to 35 microseconds, to greater than or equal to 35 microseconds when the light source luminance change period is 35 to 54 microseconds, to greater than or equal to 54 microseconds when the light source luminance change period is 54 to 74 microseconds, and to greater than or equal to 74 microseconds when the light source luminance change period is greater than or equal to 74 microseconds. 
       FIG. 24I  illustrates the relation between the exposure time t E  and the recognition success rate. Since the exposure time t E  is relative to the time during which the light source luminance is constant, the horizontal axis represents the value (relative exposure time) obtained by dividing the light source luminance change period t S  by the exposure time t E . It can be understood from the graph that the recognition success rate of approximately 100% can be attained by setting the relative exposure time to less than or equal to 1.2. For example, the exposure time may be set to less than or equal to approximately 0.83 millisecond in the case where the transmission signal is 1 kHz. Likewise, the recognition success rate greater than or equal to 95% can be attained by setting the relative exposure time to less than or equal to 1.25, and the recognition success rate greater than or equal to 80% can be attained by setting the relative exposure time to less than or equal to 1.4. Moreover, since the recognition success rate sharply decreases when the relative exposure time is about 1.5 and becomes roughly 0% when the relative exposure time is 1.6, it is necessary to set the relative exposure time not to exceed 1.5. After the recognition rate becomes 0% at  7507   c , it increases again at  7507   d ,  7507   e , and  7507   f . Accordingly, for example to capture a bright image with a longer exposure time, the exposure time may be set so that the relative exposure time is 1.9 to 2.2, 2.4 to 2.6, or 2.8 to 3.0. Such an exposure time may be used, for instance, as an intermediate mode in  FIG. 335 . 
     Depending on imaging devices, there is a time (blanking) during which no exposure is performed, as illustrated in  FIG. 25 . 
     In the case where there is blanking, the luminance of the light emitting unit during the time cannot be observed. 
     A transmission loss caused by blanking can be prevented by the light emitting unit repeatedly transmitting the same signal two or more times or adding error correcting code. 
     To prevent the same signal from being transmitted during blanking every time, the light emitting unit transmits the signal in a period that is relatively prime to the period of image capture or a period that is shorter than the period of image capture. 
     (Signal Modulation Scheme) 
     In the case of using visible light as a carrier, by causing the light emitting unit to emit light so as to keep a constant moving average of the luminance of the light emitting unit when the temporal resolution (about 5 milliseconds to 20 milliseconds) of human vision is set as a window width, the light emitting unit of the transmission device appears to be emitting light with uniform luminance to the person (human) while the luminance change of the light emitting unit is observable by the reception device, as illustrated in  FIG. 26 . 
     A modulation method illustrated in  FIG. 27  is available as a modulation scheme for causing the light emitting unit to emit light so as to keep the constant moving average of the luminance of the light emitting unit when the temporal resolution of human vision is set as the window width. Suppose a modulated signal “0” indicates no light emission and a modulated signal “1” Indicates light emission, and there is no bias in a transmission signal. Then, the average of the luminance of the light emitting unit is about 50% of the luminance at the time of light emission. 
     It is assumed here that the switching between light emission and no light emission is sufficiently fast as compared with the temporal resolution of human vision. 
     A modulation method illustrated in  FIG. 28  is available as a modulation scheme for causing the light emitting unit to emit light so as to keep the constant moving average of the luminance of the light emitting unit when the temporal resolution of human vision is set as the window width. Suppose a modulated signal “0” indicates no light emission and a modulated signal “1” indicates light emission, and there is no bias in a transmission signal. Then, the average of the luminance of the light emitting unit is about 75% of the luminance at the time of light emission. 
     When compared with the modulation scheme in  FIG. 27 , the coding efficiency is equal at 0.5, but the average luminance can be increased. 
     A modulation method illustrated in  FIG. 29  is available as a modulation scheme for causing the light emitting unit to emit light so as to keep the constant moving average of the luminance of the light emitting unit when the temporal resolution of human vision is set as the window width. Suppose a modulated signal “0” indicates no light emission and a modulated signal “1” indicates light emission, and there is no bias in a transmission signal. Then, the average of the luminance of the light emitting unit is about 87.5% of the luminance at the time of light emission. 
     When compared with the modulation schemes in  FIGS. 27 and 28 , the coding efficiency is lower at 0.375, but high average luminance can be maintained. 
     Likewise, such modulation that trades off the coding efficiency for increased average luminance is further available. 
     A modulation method illustrated in  FIG. 30  is available as a modulation scheme for causing the light emitting unit to emit light so as to keep the constant moving average of the luminance of the light emitting unit when the temporal resolution of human vision is set as the window width. 
     Suppose a modulated signal “0” indicates no light emission and a modulated signal “1” indicates light emission, and there is no bias in a transmission signal. Then, the average of the luminance of the light emitting unit is about 25% of the luminance at the time of light emission. 
     By combining this with the modulation scheme in  FIG. 28  or the like and periodically switching between the modulation schemes, it is possible to cause the light emitting unit to appear to be blinking to the person or the imaging device whose exposure time is long. 
     Likewise, by changing the modulation method, it is possible to cause the light emitting unit to appear to be emitting light with an arbitrary luminance change to the person or the imaging device whose exposure time is long. 
     In the case of using visible light as a carrier, by causing the light emitting unit to emit light so as to periodically change the moving average of the luminance of the light emitting unit when the temporal resolution of human vision is set as the window width, the light emitting unit of the transmission device appears to be blinking or changing with an arbitrary rhythm to the person while the light emission signal is observable by the reception device, as illustrated in  FIG. 31 . 
     The same advantageous effect can be obtained even in the case where an LED unit of a liquid crystal television which uses an LED light source as a backlight is caused to emit light. In this case, at least by reducing the contrast of the screen portion of an optical communication unit to be closer to white, optical communication with a low error rate can be achieved. Making the entire surface or the screen portion used for communication white contributes to a higher communication speed. 
     In the case of using a television display or the like as the light emitting unit, by adjusting, to the luminance of an image desired to be seen by the person, the moving average of the luminance of the light emitting unit when the temporal resolution of human vision is set as the window width, normal television video is seen by the person while the light emission signal is observable by the reception device, as illustrated in  FIG. 32 . 
     By adjusting, to a signal value in the case of performing signal transmission per frame, the moving average of the luminance of the light emitting unit when a substantial time per frame of the captured image is set as the window width, signal propagation can be carried out at two different speeds in such a manner that observes the light emission state of the transmission device per exposure line in the case of image capture at a short distance and observes the light emission state of the transmission device per frame in the case of image capture at a long distance, as illustrated in  FIG. 33 . 
     Note that, in the case of image capture at a short distance, the signal receivable in the case of image capture at a long distance can be received, too. 
       FIG. 34  is a diagram illustrating how light emission is observed for each exposure time. 
     The luminance of each capture pixel is proportional to the average luminance of the imaging object in the time during which the imaging element is exposed. Accordingly, if the exposure time is short, a light emission pattern  2217   a  itself is observed as illustrated in  2217   b . If the exposure time is longer, the light emission pattern  2217   a  is observed as illustrated in  2217   c ,  2217   d , or  2217   e.    
     Note that  2217   a  corresponds to a modulation scheme that repeatedly uses the modulation scheme in  FIG. 28  in a fractal manner. 
     The use of such a light emission pattern enables simultaneous transmission of more information to a reception device that includes an imaging device of a shorter exposure time and less information to a reception device that includes an imaging device of a longer exposure time. 
     The reception device recognizes that “1” is received if the luminance of pixels at the estimated position of the light emitting unit is greater than or equal to predetermined luminance and that “0” is received if the luminance of pixels at the estimated position of the light emitting unit is less than or equal to the predetermined luminance, for one exposure line or for a predetermined number of exposure lines. 
     In the case where “1” continues, it is indistinguishable from an ordinary light emitting unit (which constantly emits light without transmitting a signal). In the case where “0” continues, it is indistinguishable from the case where no light emitting unit is present. 
     Therefore, the transmission device may transmit a different numeric when the same numeric continues for a predetermined number of times. 
     Alternatively, transmission may be performed separately for a header unit that always includes “1” and “0” and a body unit for transmitting a signal, as illustrated in  FIG. 35 . In this case, the same numeric never appears more than five successive times. 
     In the case where the light emitting unit is situated at a position not shown on part of exposure lines or there is blanking, it is impossible to capture the whole state of the light emitting unit by the imaging device of the reception device. 
     This makes it necessary to indicate which part of the whole signal the transmitted signal corresponds to. 
     In view of this, there is a method whereby a data unit and an address unit indicating the position of the data are transmitted together, as illustrated in  FIG. 36 . 
     For easier signal reception at the reception device, it is desirable to set the length of the light emission pattern combining the data unit and the address unit to be sufficiently short so that the light emission pattern is captured within one image in the reception device. 
     There is also a method whereby the transmission device transmits a reference unit and a data unit and the reception device recognizes the position of the data based on the difference from the time of receiving the reference unit, as illustrated in  FIG. 37 . 
     There is also a method whereby the transmission device transmits a reference unit, an address pattern unit, and a data unit and the reception device obtains each set of data of the data unit and the pattern of the position of each set of data from the address pattern unit following the reference unit, and recognizes the position of each set of data based on the obtained pattern and the difference between the time of receiving the reference unit and the time of receiving the data, as illustrated in  FIG. 38 . 
     When a plurality of types of address patterns are available, not only data can be transmitted uniformly, but also important data or data to be processed first can be transmitted earlier than other data or repeatedly transmitted a larger number of times than other data. 
     In the case where the light emitting unit is not shown on all exposure lines or there is blanking, it is impossible to capture the whole state of the light emitting unit by the imaging device of the reception device. 
     Adding a header unit allows a signal separation to be detected and an address unit and a data unit to be detected, as illustrated in  FIG. 39 . 
     Here, a pattern not appearing in the address unit or the data unit is used as the light emission pattern of the header unit. 
     For example, the light emission pattern of the header unit may be “0011” in the case of using the modulation scheme of table  2200 . 2   a.    
     Moreover, when the header unit pattern is “11110011”, the average luminance is equal to the other parts, with it being possible to suppress flicker when seen with the human eye. Since the header unit has a high redundancy, information can be superimposed on the header unit. As an example, it is possible to indicate, with the header unit pattern “11100111”, that data for communication between transmission devices is transmitted. 
     For easier signal reception at the reception device, it is desirable to set the length of the light emission pattern combining the data unit, the address unit, and the header unit to be sufficiently short so that the light emission pattern is captured within one image in the reception device. 
     In  FIG. 40 , the transmission device determines the information transmission order according to priority. 
     For example, the number of transmissions is set in proportion to the priority. 
     In the case where the light emitting unit of the transmission device is not wholly shown on the imaging unit of the reception device or there is blanking, the reception device cannot receive signals continuously. Accordingly, information with higher transmission frequency is likely to be received earlier. 
       FIG. 41  illustrates a pattern in which a plurality of transmission devices located near each other transmit information synchronously. 
     When the plurality of transmission devices simultaneously transmit common information, the plurality of transmission devices can be regarded as one large transmission device. Such a transmission device can be captured in a large size by the imaging unit of the reception device, so that information can be received faster from a longer distance. 
     Each transmission device transmits individual information during a time slot when the light emitting unit of the nearby transmission device emits light uniformly (transmits no signal), to avoid confusion with the light emission pattern of the nearby transmission device. 
     Each transmission device may receive, at its light receiving unit, the light emission pattern of the nearby transmission signal to learn the light emission pattern of the nearby transmission device, and determine the light emission pattern of the transmission device itself. Moreover, each transmission device may receive, at its light receiving unit, the light emission pattern of the nearby transmission signal, and determine the light emission pattern of the transmission device itself according to an instruction from the other transmission device. Alternatively, each transmission device may determine the light emission pattern according to an instruction from a centralized control device. 
     (Light Emitting Unit Detection) 
     As a method of determining in which part of the image the light emitting unit is captured, there is a method whereby the number of lines on which the light emitting unit is captured is counted in the direction perpendicular to the exposure lines and the column in which the light emitting unit is captured most is set as the column where the light emitting unit is present, as illustrated in  FIG. 42 . 
     The decree of light reception fluctuates in the parts near the edges of the light emitting unit, which tends to cause wrong determination of whether or not the light emitting unit is captured. Therefore, signals are extracted from the imaging results of the pixels in the center column of all columns in each of which the light emitting unit is captured most. 
     As a method of determining in which part of the image the light emitting unit is captured, there is a method whereby the midpoint of the part in which the light emitting unit is captured is calculated for each exposure line and the light emitting unit is estimated to be present on an approximate line (straight line or quadratic curve) connecting the calculated points, as illustrated in  FIG. 43 . 
     Moreover, as illustrated in  FIG. 44 , the estimated position of the light emitting unit may be updated from the information of the current frame, by using the estimated position of the light emitting unit in the previous frame as a prior probability. 
     Here, the current estimated position of the light emitting unit may be updated based on values of a 9-axis sensor and a gyroscope during the time. 
     In  FIG. 45 , when capturing a light emitting unit  2212   b  in an imaging range  2212   a , images such as captured images  2212   c ,  2212   d , and  2212   e  are obtained. 
     Summing the light emission parts of the captured images  2212   c ,  2212   d , and  2212   e  yields a synthetic image  2212   f . The position of the light emitting unit in the captured image can thus be specified. 
     The reception device detects ON/OFF of light emission of the light emitting unit, from the specified position of the light emitting unit. 
     In the case of using the modulation scheme in  FIG. 28 , the light emission probability is 0.75, so that the probability of the light emitting unit in the synthetic image  2212   f  appearing to emit light when summing n images is 1-0.25 n . For example, when n=3, the probability is about 0.984. 
     Here, higher accuracy is attained when the orientation of the imaging unit is estimated from sensor values of a gyroscope and a 9-axis sensor and the imaging direction is compensated for before the image synthesis. In the case where the number of images to be synthesized is small, however, the imaging time is short, and so there is little adverse effect even when the imaging direction is not compensated for. 
       FIG. 46  is a diagram illustrating a situation where the reception device captures a plurality of light emitting units. 
     In the case where the plurality of light emitting units transmit the same signal, the reception device obtains one transmission signal from both light emission patterns. In the case where the plurality of light emitting units transmit different signals, the reception device obtains different transmission signals from different light emission patterns. 
     The difference in data value at the same address between the transmission signals means different signals are transmitted. 
     Whether the signal same as or different from the nearby transmission device is transmitted may be determined based on the pattern of the header unit of the transmission signal. 
     It may be assumed that the same signal is transmitted in the case where the light emitting units are substantially adjacent to each other. 
       FIG. 47  illustrates transmission signal timelines and an image obtained by capturing the light emitting units in this case. 
     (Signal Transmission Using Position Pattern) 
     In  FIG. 48 , light emitting units  2216   a ,  2216   c , and  2216   e  are emitting light uniformly, while light emitting units  2216   b ,  2216   d , and  2216   f  are transmitting signals using light emission patterns. 
     Note that the light emitting units  2216   b ,  2216   d , and  2216   f  may be simply emitting light so as to appear as stripes when captured by the reception device on an exposure line basis. 
     In  FIG. 48 , the light emitting units  2216   a  to  2216   f  may be light emitting units of the same transmission device or separate transmission devices. 
     The transmission device expresses the transmission signal by the pattern (position pattern) of the positions of the light emitting units engaged in signal transmission and the positions of the light emitting units not engaged in signal transmission. 
     In  FIG. 48 , there are six light emitting units, so that signals of 2 6 =64 values are transmittable. Though position patterns that appear to be the same when seen from different directions should not be used, such patterns can be discerned by specifying the imaging direction by the 9-axis sensor or the like in the reception device. Here, more signals may be transmitted by changing, according to time, which light emitting units are engaged in signal transmission. 
     The transmission device may perform signal transmission using the position pattern during one time slot and perform signal transmission using the light emission pattern during another time slot. For instance, all light emitting units may be synchronized during a time slot to transmit the ID or position information of the transmission device using the light emission pattern. 
     Since there are nearly an infinite number of light emitting unit arrangement patterns, it is difficult for the reception device to store all position patterns beforehand. 
     Hence, the reception device obtains a list of nearby position patterns from a server and analyzes the position pattern based on the list, using the ID or position information of the transmission device transmitted from the transmission device using the light emission pattern, the position of the reception device estimated by a wireless base station, and the position information of the reception device estimated by a GPS, a gyroscope, or a 9-axis sensor as a key. 
     According to this method, the signal expressed by the position pattern does not need to be unique in the whole world, as long as the same position pattern is not situated nearby (radius of about several meters to 300 meters). This solves the problem that a transmission device with a small number of light emitting units can express only a small number of position patterns. 
     The position of the reception device can be estimated from the size, shape, and position information of the light emitting units obtained from the server, the size and shape of the captured position pattern, and the lens characteristics of the imaging unit. 
     (Reception Device) 
     Examples of a communication device that mainly performs reception include a mobile phone, a digital still camera, a digital video camera, a head-mounted display, a robot (cleaning, nursing care, Industrial, etc.), and a surveillance camera as illustrated in  FIG. 49 , though the reception device is not limited to such. 
     Note that the reception device is a communication device that mainly receives signals, and may also transmit signals according to the method in this embodiment or other methods. 
     (Transmission Device) 
     Examples of a communication device that mainly performs transmission include a lighting (household, store, office, underground city, street, etc.), a flashlight, a home appliance, a robot, and other electronic devices as illustrated in  FIG. 50 , though the transmission device is not limited to such. 
     Note that the transmission device is a communication device that mainly transmits signals, and may also receive signals according to the method in this embodiment or other methods. 
     The light emitting unit is desirably a device that switches between light emission and no light emission at high speed such as an LED lighting or a liquid crystal display using an LED backlight as illustrated in  FIG. 51 , though the light emitting unit is not limited to such. 
     Other examples of the light emitting unit include lightings such as a fluorescent lamp, an incandescent lamp, a mercury vapor lamp, and an organic EL display. 
     Since the transmission efficiency increases when the light emitting unit is captured in a larger size, the transmission device may include a plurality of light emitting units that emit light synchronously as illustrated in  FIG. 52 . Moreover, since the transmission efficiency increases when the light emitting unit is shown in a larger size in the direction perpendicular to the exposure lines of the imaging element, the light emitting units may be arranged in a line. The light emitting units may also be arranged so as to be perpendicular to the exposure lines when the reception device is held normally. In the case where the light emitting unit is expected to be captured in a plurality of directions, the light emitting units may be arranged in the shape of a cross as illustrated in  FIG. 53 . Alternatively, in the case where the light emitting unit is expected to be captured in a plurality of directions, a circular light emitting unit may be used or the light emitting units may be arranged in the shape of a circle as illustrated in  FIG. 54 . Since the transmission efficiency increases when the light emitting unit is captured in a larger size, the transmission device may cover the light emitting unit(s) with a diffusion plate as illustrated in  FIG. 55 . 
     Light emitting units that transmit different signals are positioned away from each other so as not to be captured at the same time, as illustrated in  FIG. 56 . As an alternative, light emitting units that transmit different signals have a light emitting unit, which transmits no signal, placed therebetween so as not to be captured at the same time, as illustrated in  FIG. 57 . 
     (Structure of Light Emitting Unit) 
       FIG. 58  is a diagram illustrating a desirable structure of the light emitting unit. 
     In  2311   a , the light emitting unit and its surrounding material have low reflectance. This eases the recognition of the light emission state by the reception device even when light impinges on or around the light emitting unit. In  2311   b , a shade for blocking external light is provided. This eases the recognition of the light emission state by the reception device because light is kept from impinging on or around the light emitting unit. In  2311   c , the light emitting unit is provided in a more recessed part. This eases the recognition of the light emission state by the reception device because light is kept from impinging on or around the light emitting unit. 
     (Signal Carrier) 
     Light (electromagnetic wave) in frequency bands from near infrared, visible light, to near ultraviolet illustrated in  FIG. 59 , which can be received by the reception device, is used as light (electromagnetic wave) for carrying signals. 
     (Imaging Unit) 
     In  FIG. 60 , an imaging unit in the reception device detects a light emitting unit  2310   b  emitting light in a pattern, in an imaging range  2310   a.    
     An imaging control unit obtains a captured image  2310   d  by repeatedly using an exposure line  2310   c  at the center position of the light emitting unit, instead of using the other exposure lines. 
     The captured image  2310   d  is an image of the same area at different exposure times. The light emission pattern of the light emitting unit can be observed by scanning, in the direction perpendicular to the exposure lines, the pixels where the light emitting unit is shown in the captured image  2310   d.    
     According to this method, even in the case where the light emitting unit is present only in one part of the captured image, the luminance change of the light emitting unit can be observed for a longer time. Hence, the signal can be read even when the light emitting unit is small or the light emitting unit is captured from a long distance. 
     In the case where there is no blanking, the method allows every luminance change of the light emitting unit to be observed so long as the light emitting unit is shown in at least one part of the imaging device. 
     In the case where the time for exposing one line is longer than the time from when the exposure of the line starts to when the exposure of the next line starts, the same advantageous effect can be achieved by capturing the image using a plurality of exposure lines at the center of the light emitting unit. 
     Note that, in the case where pixel-by-pixel control is possible, the image is captured using only a point closest to the center of the light emitting unit or only a plurality of points closest to the center of the light emitting unit. Here, by making the exposure start time of each pixel different, the light emission state of the light emitting unit can be detected in smaller periods. 
     When, while mainly using the exposure line  2310   c , other exposure lines are occasionally used and the captured images are synthesized, the synthetic image (video) that is similar to the normally captured image though lower in resolution or frame rate can be obtained. The synthetic image is then displayed to the user, so that the user can operate the reception device or perform image stabilization using the synthetic image. 
     The image stabilization may be performed using sensor values of a gyroscope, a 9-axis sensor, and the like, or using an image captured by an imaging device other than the imaging device capturing the light emitting unit. 
     It is desirable to use exposure lines or exposure pixels in a part near the center of the light emitting unit rather than near the edges of the light emitting unit, because the light emitting unit is less likely to be displaced from such exposure lines or exposure pixels upon hand movement. 
     Since the periphery of the light emitting unit is low in luminance, it is desirable to use exposure lines or exposure pixels in a part that is as far from the periphery of the light emitting unit as possible and is high in luminance. 
     (Position Estimation of Reception Device) 
     In  FIG. 61 , the transmission device transmits the position information of the transmission device, the size of the light emitting device, the shape of the light emitting device, and the ID of the transmission device. The position information includes the latitude, longitude, altitude, height from the floor surface, and the like of the center part of the light emitting device. 
     The reception device estimates the imaging direction based on information obtained from the 9-axis sensor and the gyroscope. The reception device estimates the distance from the reception device to the light emitting device, from the size and shape of the light emitting device transmitted from the transmission device, the size and shape of the light emitting device in the captured image, and information about the imaging device. The information about the imaging device includes the focal length of a lens, the distortion of the lens, the size of the imaging element, the distance between the lens and the imaging element, a comparative table of the size of an object of a reference size in the captured image and the distance from the imaging device to the imaging object, and so on. 
     The reception device also estimates the position information of the reception device, from the information transmitted from the transmission device, the imaging direction, and the distance from the reception device to the light emitting device. 
     In  FIG. 62 , the transmission device transmits the position information of the transmission device, the size of the light emitting unit, the shape of the light emitting unit, and the ID of the transmission device. The position information includes the latitude, longitude, altitude, height from the floor surface, and the like of the center part of the light emitting unit. 
     The reception device estimates the imaging direction based on information obtained from the 9-axis sensor and the gyroscope. The reception device estimates the distance from the reception device to the light emitting unit, from the size and shape of the light emitting unit transmitted from the transmission device, the size and shape of the light emitting unit in the captured image, and information about the imaging device. The information about the imaging device includes the focal length of a lens, the distortion of the lens, the size of the imaging element, the distance between the lens and the imaging element, a comparative table of the size of an object of a reference size in the captured image and the distance from the imaging device to the imaging object, and so on. 
     The reception device also estimates the position information of the reception device, from the information transmitted from the transmission device, the imaging direction, and the distance from the reception device to the light emitting unit. The reception device estimates the moving direction and the moving distance, from the information obtained from the 9-axis sensor and the gyroscope. The reception device estimates the position information of the reception device, using position information estimated at a plurality of points and the position relation between the points estimated from the moving direction and the moving distance. 
     For example, suppose the random field of the position information of the reception device estimated at point [Math. 1] x 1  is [Math. 2] P x1 , and the random field of the moving direction and the moving distance estimated when moving from point [Math. 3] x 1  to point [Math. 4] x 2  is [Math. 5] M x1x2 . Then, the random field of the eventually estimated position information can be calculated at 
     
       
         
           
             
               
                 
                   
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     Moreover, in  FIG. 62 , the transmission device may transmit the position information of the transmission device and the ID of the transmission device. The position information includes the latitude, longitude, altitude, height from the floor surface, and the like of the center part of the light emitting device. 
     In this case, the reception device estimates the imaging direction based on information obtained from the 9-axis sensor and the gyroscope. The reception device estimates the position information of the reception device by trilateration. 
     In  FIG. 63 , the transmission device transmits the ID of the transmission device. 
     The reception device receives the ID of the transmission device, and obtains the position information of the transmission device, the size of the light emitting device, the shape of the light emitting device, and the like from the Internet. The position information includes the latitude, longitude, altitude, height from the floor surface, and the like of the center part of the light emitting device. 
     The reception device estimates the imaging direction based on information obtained from the 9-axis sensor and the gyroscope. The reception device estimates the distance from the reception device to the light emitting device, from the size and shape of the light emitting device transmitted from the transmission device, the size and shape of the light emitting device in the captured image, and information about the imaging device. The information about the imaging device includes the focal length of a lens, the distortion of the lens, the size of the imaging element, the distance between the lens and the imaging element, a comparative table of the size of an object of a reference size in the captured image and the distance from the imaging device to the imaging object, and so on. 
     The reception device also estimates the position information of the reception device, from the information obtained from the Internet, the imaging direction, and the distance from the reception device to the light emitting device. 
     In  FIG. 64 , the transmission device transmits the position information of the transmission device and the ID of the transmission device. The position information includes the latitude, longitude, altitude, height from the floor surface, and the like of the center part of the light emitting device. 
     The reception device estimates the imaging direction based on information obtained from the 9-axis sensor and the gyroscope. The reception device estimates the position information of the reception device by triangulation. 
     In  FIG. 65 , the transmission device transmits the position information of the transmission device and the ID of the transmission device. The position information includes the latitude, longitude, altitude, height from the floor surface, and the like of the center part of the light emitting device. 
     The reception device estimates the imaging direction based on information obtained from the 9-axis gyroscope. The reception device estimates the position information of the reception device by triangulation. The reception device also estimates the orientation change and movement of the reception device, from the gyroscope and the 9-axis sensor. The reception device may perform zero point adjustment or calibration of the 9-axis sensor simultaneously. 
     (Transmission Information Setting) 
     In  FIG. 66 , a reception device  2606   c  obtains a transmitted signal by capturing a light emission pattern of a transmission device  2606   b , and estimates the position of the reception device. 
     The reception device  2606   c  estimates the moving distance and direction from the change in captured image and the sensor values of the 9-axis sensor and the gyroscope, during movement. 
     The reception device captures a light receiving unit of a transmission device  2606   a , estimates the center position of the light emitting unit, and transmits the position to the transmission device. 
     Since the size information of the light emitting device is necessary for estimating the position of the light emitting unit, the transmission device desirably transmits the size information of the light emitting unit even in the case where part of the transmission information is missing. In the case where the size of the light emitting unit is unknown, the reception device estimates the height of the ceiling from the distance between the transmission device  2606   b  and the reception device  2606   c  used in the position estimation and, through the use of this estimation result, estimates the distance between the transmission device  2606   a  and the reception device  2606   c.    
     There are transmission methods such as transmission using a light emission pattern, transmission using a sound pattern, and transmission using a radio wave. The light emission pattern of the transmission device and the corresponding time may be stored and later transmitted to the transmission device or the centralized control device. 
     The transmission device or the centralized control device specifies, based on the light emission pattern and the time, the transmission device captured by the reception device, and stores the position information in the transmission device. 
     In  FIG. 67 , a position setting point is designated by designating one point of the transmission device as a point in the image captured by the reception device. 
     The reception device calculates the position relation to the center of the light emitting unit of the transmission device from the position setting point, and transmits, to the transmission device, the position obtained by adding the position relation to the setting point. 
     In  FIG. 68 , the reception device receives the transmitted signal by capturing the image of the transmission device. The reception device communicates with a server or an electronic device based on the received signal. 
     As an example, the reception device obtains the information of the transmission device, the position and size of the transmission device, service information relating to the position, and the like from the server, using the ID of the transmission device included in the signal as a key. 
     As another example, the reception device estimates the position of the reception device from the position of the transmission device included in the signal, and obtains map information, service information relating to the position, and the like from the server. 
     As yet another example, the reception device obtains a modulation scheme of a nearby transmission device from the server, using the rough current position as a key. 
     As yet another example, the reception device registers, in the server, the position information of the reception device or the transmission device, neighborhood information, and information of any process performed by the reception device in the neighborhood, using the ID of the transmission device included in the signal as a key. 
     As yet another example, the reception device operates the electronic device, using the ID of the transmission device included in the signal as a key. 
     (Block Diagram of Reception Device) 
       FIG. 69  is a block diagram illustrating the reception device. The reception device includes all of the structure or part of the structure including an imaging unit and a signal analysis unit. In  FIG. 69 , blocks having the same name may be realized by the same structural element or different structural elements. 
     A reception device  2400   af  in a narrow sense is included in a smartphone, a digital camera, or the like. An input unit  2400   h  includes all or part of: a user operation input unit  2400   i ; a light meter  2400   j ; a microphone  2400   k ; a timer unit  2400   n ; a position estimation unit  2400   m ; and a communication unit  2400   p.    
     An imaging unit  2400   a  includes all or part of: a lens  2400   b ; an imaging element  2400   c ; a focus control unit  2400   d ; an imaging control unit  2400   e ; a signal detection unit  2400   f ; and an imaging information storage unit  2400   g . The imaging unit  2400   a  starts imaging according to a user operation, an illuminance change, or a sound or voice pattern, when a specific time is reached, when the reception device moves to a specific position, or when instructed by another device via a communication unit. 
     The focus control unit  2400   d  performs control such as adjusting the focus to a light emitting unit  2400   ae  of the transmission device or adjusting the focus so that the light emitting unit  2400   ae  of the transmission device is shown in a large size in a blurred state. 
     An exposure control unit  2400   ak  sets an exposure time and an exposure gain. 
     The imaging control unit  2400   e  limits the position to be captured, to specific pixels. 
     The signal detection unit  2400   f  detects pixels including the light emitting unit  2400   ae  of the transmission device or pixels including the signal transmitted using light emission, from the captured image. 
     The imaging information storage unit  2400   g  stores control information of the focus control unit  2400   d , control information of the imaging control unit  2400   e , and information detected by the signal detection unit  2400   f . In the case where there are a plurality of imaging devices, imaging may be simultaneously performed by the plurality of imaging devices so that one of the captured images is put to use in estimating the position or orientation of the reception device. 
     A light emission control unit  2400   ad  transmits a signal by controlling the light emission pattern of the light emitting unit  2400   ae  according to the input from the input unit  2400   h . The light emission control unit  2400   ad  obtains, from a timer unit  2400   ac , the time at which the light emitting unit  2400   ae  emits light, and records the obtained time. 
     A captured image storage unit  2400   w  stores the image captured by the imaging unit  2400   a.    
     A signal analysis unit  2400   y  obtains the transmitted signal from the captured light emission pattern of the light emitting unit  2400   ae  of the transmission device through the use of the difference between exposure times of lines in the imaging element, based on a modulation scheme stored in the modulation scheme storage unit  2400   af.    
     A received signal storage unit  2400   z  stores the signal analyzed by the signal analysis unit  2400   y.    
     A sensor unit  2400   q  includes all or part of: a GPS  2400   r ; a magnetic sensor  2400   t ; an accelerometer  2400   s ; and a gyroscope  2400   u . The magnetic sensor  2400   t  and the accelerometer  2400   s  may each be a 9-axis sensor. 
     A position estimation unit estimates the position or orientation of the reception device, from the information from the sensor unit, the captured image, and the received signal. 
     A computation unit  2400   aa  causes a display unit  2400   ab  to display the received signal, the estimated position of the reception device, and information (e.g. information relating to a map or locations, information relating to the transmission device) obtained from a network  2400   ah  based on the received signal or the estimated position of the reception device. 
     The computation unit  2400   aa  controls the transmission device based on the information input to the input unit  2400   h  from the received signal or the estimated position of the reception device. 
     A communication unit  2400   ag  performs communication between terminals without via the network  2400   ah , in the case of using a peer-to-peer connection scheme (e.g. Bluetooth). 
     An electronic device  2400   aj  is controlled by the reception device. 
     A server  2400   ai  stores the information of the transmission device, the position of the transmission device, and information relating to the position of the transmission device, in association with the ID of the transmission device. 
     The server  2400   ai  stores the modulation scheme of the transmission device in association with the position. 
     (Block Diagram of Transmission Device) 
       FIG. 70  is a block diagram illustrating the transmission device. 
     The transmission device includes all of the structure or part of the structure including a light emitting unit, a transmission signal storage unit, a modulation scheme storage unit, and a computation unit. 
     A transmission device  2401   ab  in a narrow sense is included in an electric light, an electronic device, or a robot. 
     A lighting control switch  2401   n  is a switch for switching the lighting ON and OFF. 
     A diffusion plate  2401   p  is a member attached near a light emitting unit  2401   q  In order to diffuse light of the light emitting unit  2401   q.    
     The light emitting unit  2401   q  is turned ON and OFF at a speed that allows the light emission pattern to be detected on a line basis, through the use of the difference between exposure times of lines in the imaging element of the reception device in  FIG. 69 . 
     The light emitting unit  2401   q  is composed of a light source, such as an LED or a fluorescent lamp, capable of turning ON and OFF at high speed. 
     A light emission control unit  2401   r  controls ON and OFF of the light emitting unit  2401   q.    
     A light receiving unit  2401   s  is composed of a light receiving element or an imaging element. The light receiving unit  2401   s  converts the intensity of received light to an electric signal. An imaging unit may be used instead of the light receiving unit  2401   s.    
     A signal analysis unit  2401   t  obtains the signal from the pattern of the light received by the light receiving unit  2401   s.    
     A computation unit  2401   u  converts a transmission signal stored in a transmission signal storage unit  2401   d  to a light emission pattern according to a modulation scheme stored in a modulation scheme storage unit  2401   e . The computation unit  2401   u  controls communication by editing information in the storage unit  2401   a  or controlling the light emission control unit  2401   r , based on the signal obtained from the signal analysis unit  2401   t . The computation unit  2401   u  controls communication by editing information in the storage unit  2401   a  or controlling the light emission control unit  2401   r , based on a signal from an attachment unit  2401   w . The computation unit  2401   u  edits information in the storage unit  2401   a  or controls the light emission control unit  2401   r , based on a signal from a communication unit  2401   v.    
     The computation unit  2401   u  also edits information in a storage unit  2401   b  in an attachment device  2401   h . The computation unit  2401   u  copies the information in the storage unit  2401   b  in the attachment device  2401   h , to a storage unit  2401   a.    
     The computation unit  2401   u  controls the light emission control unit  2401   r  at a specified time. The computation unit  2401   u  controls an electronic device  2401   zz  via a network  2401   aa.    
     The storage unit  2401   a  Includes all or part of: the transmission signal storage unit  2401   d ; a shape storage unit  2401   f ; the modulation scheme storage unit  2401   e ; and a device state storage unit  2401   g.    
     The transmission signal storage unit  2401   d  stores the signal to be transmitted from the light emitting unit  2401   q.    
     The modulation scheme storage unit  2401   e  stores the modulation scheme for converting the transmission signal to the light emission pattern. 
     The shape storage unit  2401   f  stores the shapes of the transmission device and light emitting unit  2401   q.    
     The device state storage unit  2401   g  stores the state of the transmission device. 
     The attachment unit  2401   w  is composed of an attachment bracket or a power supply port. 
     The storage unit  2401   b  in the attachment device  2401   h  stores information stored in the storage unit  2401   a . Here, the storage unit  2401   b  in the attachment device  2401   h  or a storage unit  2401   c  in a centralized control device  2401   m  may be used, while omitting the storage unit  2401   a.    
     A communication unit  2401   v  performs communication between terminals without via the network  2400   aa , in the case of using a peer-to-peer connection scheme (e.g. Bluetooth). 
     A server  2401   y  stores the information of the transmission device, the position of the transmission device, and information relating to the position of the transmission device, in association with the ID of the transmission device. The server  2401   y  also stores the modulation scheme of the transmission device in association with the position. 
     (Reception procedure) 
       FIG. 71  is explained below. In Step  2800   a , whether or not there are a plurality of imaging devices in the reception device is determined. In the case of No, the procedure proceeds to Step  2800   b  to select an imaging device to be used, and then proceeds to Step  2800   c . In the case of Yes, on the other hand, the procedure proceeds to Step  2800   c.    
     In Step  2800   c , an exposure time (=shutter speed) is set (the exposure time is desirably shorter). 
     Next, in Step  2800   d , an exposure gain is set. 
     Next, in Step  2800   e , an image is captured. 
     Next, in Step  2800   f , a part having at least a predetermined number of consecutive pixels whose luminance exceeds a predetermined threshold is determined for each exposure line, and the center position of the part is calculated. 
     Next, in Step  2800   g , a linear or quadratic approximate line connecting the above center positions is calculated. 
     Next, in Step  2800   h , the luminance of the pixel on the approximate line in each exposure line is set as the signal value of the exposure line. 
     Next, in Step  2800   i , an assigned time per exposure line is calculated from imaging information including an imaging frame rate, a resolution, a blanking time, and the like. 
     Next, in Step  2800   j , in the case where the blanking time is less than or equal to a predetermined time, it is determined that the exposure line following the last exposure line of one frame is the first exposure line of the next frame. In the case where the blanking time is greater than the predetermined time, it is determined that unobservable exposure lines as many as the number obtained by dividing the blanking time by the assigned time per exposure line are present between the last exposure line of one frame and the first exposure line of the next frame. 
     Next, in Step  2800   k , a reference position pattern and an address pattern are read from decoded information. 
     Next, in Step  2800   m , a pattern indicating a reference position of the signal is detected from the signal of each exposure line. 
     Next, in Step  2800   n , a data unit and an address unit are calculated based on the detected reference position. 
     Next, in Step  2800   p , a transmission signal is obtained. 
     (Self-Position Estimation Procedure) 
       FIG. 72  is explained below. First, in Step  2801   a , a position recognized as the current position of the reception device or a current position probability map is set as self-position prior information. 
     Next, in Step  2801   b , the imaging unit of the reception device is pointed to the light emitting unit of the transmission device. 
     Next, in Step  2801   c , the pointing direction and elevation angle of the imaging device are calculated from the sensor values of the 9-axis sensor and the gyroscope. 
     Next, in Step  2801   d , the light emission pattern is captured and the transmission signal is obtained. 
     Next, in Step  2801   e , the distance between the imaging device and the light emitting unit is calculated from information of the size and shape of the light emitting unit included in the transmission signal, the size of the captured light emitting unit, and the imaging magnification factor of the imaging device. 
     Next, in Step  2801   f , the relative angle between the direction from the imaging unit to the light emitting unit and the normal line of the imaging plane is calculated from the position of the light emitting unit in the captured image and the lens characteristics. 
     Next, in Step  2801   g , the relative position relation between the imaging device and the light emitting unit is calculated from the hitherto calculated values. 
     Next, in Step  2801   h , the position of the reception device is calculated from the position of the light emitting unit included in the transmission signal and the relative position relation between the imaging device and the light emitting unit. Note that, when a plurality of transmission devices can be observed, the position of the reception device can be calculated with high accuracy by calculating the coordinates of the imaging device from the signal included in each transmission device. When a plurality of transmission devices can be observed, triangulation is applicable. 
     Next, in Step  2801   i , the current position or current position probability map of the reception device is updated from the self-position prior information and the calculation result of the position of the reception device. 
     Next, in Step  2801   j , the imaging device is moved. 
     Next, in Step  2801   k , the moving direction and distance are calculated from the sensor values of the 9-axis sensor and the gyroscope. 
     Next, in Step  2801   m , the moving direction and distance are calculated from the captured image and the orientation of the imaging device. The procedure then returns to Step  2801   a.    
     (Transmission Control Procedure 1) 
       FIG. 73  is explained below. First, in Step  2802   a , the user presses a button. 
     Next, in Step  2802   b , the light emitting unit is caused to emit light. Here, a signal may be expressed by the light emission pattern. 
     Next, in Step  2802   c , the light emission start time and end time and the time of transmission of a specific pattern are recorded. 
     Next, in Step  2802   d , the image is captured by the imaging device. 
     Next, in Step  2802   e , the image of the light emission pattern of the transmission device present in the captured image is captured, and the transmitted signal is obtained. Here, the light emission pattern may be synchronously analyzed using the recorded time. 
     The procedure then ends. 
     (Transmission Control Procedure 2) 
       FIG. 74  is explained below. First, in Step  2803   a , light is received by the light receiving device or the image is captured by the imaging device. 
     Next, in Step  2803   b , whether or not the pattern is a specific pattern is determined. 
     In the case of No, the procedure returns to Step  2803   a . In the case of Yes, on the other hand, the procedure proceeds to Step  2803   c  to record the start time and end time of light reception or image capture of the reception pattern and the time of appearance of the specific pattern. 
     Next, in Step  2803   d , the transmission signal is read from the storage unit and converted to the light emission pattern. 
     Next, in Step  2803   e , the light emitting unit is caused to emit light according to the light emission pattern, and the procedure ends. Here, the light emission may be started after a predetermined time period from the recorded time, with the procedure ending thereafter. 
     (Transmission Control Procedure 3) 
       FIG. 75  is explained below. First, in Step  2804   a , light is received by the light receiving device, and the received light energy is converted to electricity and accumulated. 
     Next, in Step  2804   b , whether or not the accumulated energy is greater than or equal to a predetermined amount is determined. 
     In the case of No, the procedure returns to Step  2804   a . In the case of Yes, on the other hand, the procedure proceeds to Step  2804   c  to analyze the received light and record the time of appearance of the specific pattern. 
     Next, in Step  2804   d , the transmission signal is read from the storage unit and converted to the light emission pattern. 
     Next, in Step  2804   e , the light emitting unit is caused to emit light according to the light emission pattern, and the procedure ends. Here, the light emission may be started after a predetermined time period from the recorded time, with the procedure ending thereafter. 
     (Information Provision Inside Station) 
       FIG. 76  is a diagram for describing a situation of receiving information provision inside a station. 
     A reception device  2700   a  captures an image of a lighting disposed in a station facility and reads a light emission pattern or a position pattern, to receive information transmitted from the lighting device. 
     The reception device  2700   a  obtains information of the lighting or the facility from a server based on the reception information, and further estimates the current position of the reception device  2700   a  from the size or shape of the captured lighting. 
     For example, the reception device  2700   a  displays information obtained based on a facility ID or position information ( 2700   b ). The reception device  2700   a  downloads a map of the facility based on the facility ID, and navigates to a boarding place using ticket information purchased by the user ( 2700   c ). 
     Though  FIG. 76  illustrates the example inside the train station, the same applies to facilities such as an airport, a harbor, a bus stop, and so on. 
     (Passenger Service) 
       FIG. 77  is a diagram illustrating a situation of use inside a vehicle. 
     A reception device  2704   a  carried by a passenger and a reception device  2704   b  carried by a salesperson each receive a signal transmitted from a lighting  2704   e , and estimates the current position of the reception device itself. 
     Note that each reception device may obtain necessary information for self-position estimation from the lighting  2704   e , obtain the information from a server using the information transmitted from the lighting  2704   e  as a key, or obtain the information beforehand based on position information of a train station, a ticket gate, or the like. 
     The reception device  2704   a  may recognize that the current position is inside the vehicle from ride time information of a ticket purchased by the user (passenger) and the current time, and download information associated with the vehicle. 
     Each reception device notifies a server of the current position of the reception device. The reception device  2704   a  notifies the server of a user (passenger) ID, a reception device ID, and ticket information purchased by the user (passenger), as a result of which the server recognizes that the person in the seat is a person entitled to riding or reserved seating. 
     The reception device  2704   a  displays the current position of the salesperson, to enable the user (passenger) to decide the purchase timing for sales aboard the train. 
     When the passenger orders an item sold aboard the train through the reception device  2704   a , the reception device  2704   a  notifies the reception device  2704   b  of the salesperson or the server of the position of the reception device  2704   a , order details, and billing information. The reception device  2704   b  of the salesperson displays a map  2704   d  indicating the position of the customer. 
     The passenger may also purchase a seat reservation ticket or a transfer ticket through the reception device  2704   a.    
     The reception device  2704   a  displays available seat information  2704   c . The reception device  2704   a  notifies the server of reserved seat ticket or transfer ticket purchase information and billing information, based on travel section information of the ticket purchased by the user (passenger) and the current position of the reception device  2704   a.    
     Though  FIG. 77  illustrates the example inside the train, the same applies to vehicles such as an airplane, a ship, a bus, and so on. 
     (In-Store Service) 
       FIG. 78  is a diagram illustrating a situation of use inside a store or a shop. 
     Reception devices  2707   b ,  2707   c , and  2707   d  each receive a signal transmitted from a lighting  2707   a , estimate the current position of the reception device itself, and notify a server of the current position. 
     Note that each reception device may obtain necessary information for self-position estimation and a server address from the lighting  2707   a , obtain the necessary information and the server address from another server using information transmitted from the lighting  2707   a  as a key, or obtain the necessary information and the server address from an accounting system. 
     The accounting system associates accounting information with the reception device  2707   d , displays the current position of the reception device  2707   d  ( 2707   c ), and delivers the ordered item. 
     The reception device  2707   b  displays item information based on the information transmitted from the lighting  2707   a . When the customer orders from the displayed item information, the reception device  2707   b  notifies the server of item information, billing information, and the current position. 
     Thus, the seller can deliver the ordered item based on the position information of the reception device  2707   b , and the purchaser can purchase the item while remaining seated. 
     (Wireless Connection Establishment) 
       FIG. 79  is a diagram illustrating a situation of communicating wireless connection authentication information to establish wireless connection. 
     An electronic device (digital camera)  2701   b  operates as a wireless connection access point and, as information necessary for the connection, transmits an ID or a password as a light emission pattern. 
     An electronic device (smartphone)  2701   a  obtains the transmission information from the light emission pattern, and establishes the wireless connection. 
     Though the wireless connection is mentioned here, the connection to be established may be a wired connection network. 
     The communication between the two electronic devices may be performed via a third electronic device. 
     (Communication Range Adjustment) 
       FIG. 80  is a diagram illustrating a range of communication using a light emission pattern or a position pattern. 
     In a communication scheme using a radio wave, it is difficult to limit the communication range because the radio wave also reaches an adjacent room separated by a wall. 
     In communication using a light emission pattern or a position pattern, on the other hand, the communication range can be easily limited using an obstacle because visible light and its surrounding area wavelengths are used. Moreover, the use of visible light has an advantage that the communication range is recognizable even by the human eye. 
     (Indoor Use) 
       FIG. 81  is a diagram illustrating a situation of indoor use such as an underground city. 
     A reception device  2706   a  receives a signal transmitted from a lighting  2706   b , and estimates the current position of the reception device  2706   a . The reception device  2706   a  also displays the current position on a map to provide directions, or displays nearby shop information. 
     By transmitting disaster information or evacuation information from the lighting  2706   b  in the event of an emergency, such information can be obtained even in the case of communication congestion, in the case of a failure of a communication base station, or in the case of being situated in a place where it is difficult for a radio wave from a communication base station to penetrate. This is beneficial to people who missed hearing emergency broadcasting or hearing-impaired people who cannot hear emergency broadcasting. 
     (Outdoor Use) 
       FIG. 82  is a diagram illustrating a situation of outdoor use such as a street. 
     A reception device  2705   a  receives a signal transmitted from a street lighting  2705   b , and estimates the current position of the reception device  2705   a . The reception device  2705   a  also displays the current position on a map to provide directions, or displays nearby shop information. 
     By transmitting disaster information or evacuation information from the lighting  2705   b  in the event of an emergency, such information can be obtained even in the case of communication congestion, in the case of a failure of a communication base station, or in the case of being situated in a place where it is difficult for a radio wave from a communication base station to penetrate. 
     Moreover, displaying the movements of other vehicles and pedestrians on the map and notifying the user of any approaching vehicles or pedestrians contributes to accident prevention. 
     (Route Indication) 
       FIG. 83  is a diagram illustrating a situation of route indication. 
     A reception device  2703   e  can download a neighborhood map or estimate the position of the reception device  2703   a  with an accuracy error of 1 cm to tens of cm, through the use of information transmitted from transmission devices  2703   a ,  2703   b , and  2703   c.    
     When the accurate position of the reception device  2703   e  is known, it is possible to automatically drive a wheelchair  2703   d  or ensure safe passage of visually impaired people. 
     (Use of a Plurality of Imaging Devices) 
     A reception device in  FIG. 84  includes an in camera  2710   a , a touch panel  2710   b , a button  2710   c , an out camera  2710   d , and a flash  2710   e.    
     When capturing the transmission device by the out camera, image stabilization can be performed by estimating the movement or orientation of the reception device from an image captured by the in camera. 
     By receiving a signal from another transmission device using the in camera, it is possible to simultaneously receive the signals from the plurality of devices or enhance the self-position estimation accuracy of the reception device. 
     (Transmission Device Autonomous Control) 
     In  FIG. 85 , a transmission device  1  receives light of a light emitting unit of a transmission device  2  by a light receiving unit, to obtain a signal transmitted from the transmission device  2  and its transmission timing. 
     In the case where no transmission signal is stored in a storage unit of the transmission device  1 , the transmission device  1  transmits a signal by emitting light in the same pattern synchronously with the light emission of the transmission device  2 . 
     In the case where a transmission signal is stored in the storage unit of the transmission device  1 , on the other hand, the transmission device  1  transmits a part common with the transmission signal of the transmission device  2  by emitting light in the same pattern synchronously with the light emission of the transmission device  2 . The transmission device  1  also transmits a part not common with the transmission signal of the transmission device  2 , during a time in which the transmission device  2  transmits no signal. In the case where there is no time in which the transmission device  2  transmits no signal, the transmission device  1  specifies a period appropriately and transmits the uncommon part according to the period. In this case, the transmission device  2  receives the light emitted from the transmission device  1  by a light receiving unit, detects that a different signal is transmitted at the same time, and transmits an uncommon part of signal during a time in which the transmission device  1  transmits no signal. 
     CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is used for avoiding collisions in signal transmission using light emission. 
     The transmission device  1  causes the light emitting unit to emit light using its own information as a light emission pattern. 
     The transmission device  2  obtains the information of the transmission device  1  by the light receiving unit. 
     The transmission device generates a transmission device arrangement map by exchanging, between communicable transmission devices, their information. The transmission device also calculates an optimal light emission pattern as a whole so as to avoid collisions in signal transmission using light emission. Further, the transmission device obtains information obtained by the other transmission device(s), through communication between the transmission devices. 
     (Transmission Information Setting) 
     In  FIG. 86 , a transmission device stores information stored in a storage unit of an attachment device into a storage unit of the transmission device, when the transmission device is attached to the attachment device or the information stored in the storage unit of the attachment device is changed. The information stored in the storage unit of the attachment device or the transmission device includes a transmission signal and its transmission timing. 
     In the case where the information stored in the storage unit is changed, the transmission device stores the information into the storage unit of the attachment device. The information in the storage unit of the attachment device or the storage unit of the transmission device is edited from a centralized control device or a switchboard. Power line communication is used when operating from the switchboard. 
     A shape storage unit in the transmission device stores a position relation between a center position of a light emitting unit and an attachment unit of the transmission device. 
     When transmitting position information, the transmission device transmits position information obtained by adding the position relation to position information stored in the storage unit. 
     Information is stored into the storage unit of the attachment device upon building construction or the like. In the case of storing position information, the accurate position is stored through the use of a design or CAD data of the building. Transmitting the position information from the transmission device upon building construction enables position identification, which may be utilized for construction automation, material use position identification, and the like. 
     The attachment device notifies the centralized control device of the information of the transmission device. The attachment device notifies the centralized control device that a device other than the transmission device is attached. 
     In  FIG. 87 , a transmission device receives light by a light receiving unit, obtains information from the light pattern by a signal analysis unit, and stores the information into a storage unit. Upon light reception, the transmission device converts information stored in the storage unit to a light emission pattern and causes a light emitting unit to emit light. 
     Information about the shape of the transmission device is stored in a shape storage unit. 
     In  FIG. 88 , a transmission device stores a signal received by a communication unit, into a storage unit. Upon reception, the transmission device converts information stored in the storage unit to a light emission pattern and causes a light emitting unit to emit light. 
     Information about the shape of the transmission device is stored in a shape storage unit. 
     In the case where no transmission signal is stored in the storage unit, the transmission device converts an appropriate signal to a light emission pattern and causes the light emitting unit to emit light. 
     A reception device obtains the signal transmitted from the transmission device by an imaging unit, and notifies a transmission device or a centralized control device of the signal and information to be stored in the transmission device, via a communication unit. 
     The transmission device or the centralized control device stores the transmitted information into the storage unit of the transmission device transmitting the same signal as the signal obtained by the imaging unit of the reception device. 
     Here, the reception device may transmit the signal transmitted from the transmission device according to the time of image capture so that the transmission device or the centralized control device specifies the transmission device captured by the reception device using the time. 
     Note that the information may be transmitted from the reception device to the transmission device using a light emission pattern, where the communication unit of the reception device is a light emitting unit and the communication unit of the transmission device is a light receiving unit or an imaging unit. 
     Alternatively, the information may be transmitted from the reception device to the transmission device using a sound pattern, where the communication unit of the reception device is a sound emitting unit and the communication unit of the transmission device is a sound receiving unit. 
     (Combination with 2D Barcode) 
       FIG. 89  is a diagram illustrating a situation of use in combination with 2D (two-dimensional) barcode. 
     The user sets a communication device  2714   a  and a communication device  2714   d  opposed to each other. 
     The communication device  2714   a  displays transmission information on a display as 2D barcode  2714   c.    
     The communication device  2714   d  reads the 2D barcode  2714   c  by a 2D barcode reading unit  2714   f . The communication device  2714   d  expresses transmission information as a light emission pattern of a light emitting unit  2714   e.    
     The communication device  2714   a  captures the light emitting unit by an imaging unit  2714   b , and reads the signal. According to this method, two-way direct communication is possible. In the case where the amount of data to be transmitted is small, faster communication can be performed than communication via a server. 
     (Map Generation and Use) 
       FIG. 90  is a diagram illustrating a situation of map generation and use. 
     A robot  2715   a  creates a room map  2715   f  by performing self-position estimation based on signals transmitted from a lighting  2715   d  and an electronic device  2715   c , and stores the map information, the position information, and the IDs of the lighting  2715   d  and the electronic device  2715   c  into a server  2715   e.    
     Likewise, a reception device  2715   b  creates the room map  2715   f  from the signals transmitted from the lighting  2715   d  and the electronic device  2715   c , an image captured during movement, and sensor values of the gyroscope and the 9-axis sensor, and stores the map information, the position information, and the IDs of the lighting  2715   d  and the electronic device  2715   c  into the server  2715   e.    
     The robot  2715   a  performs cleaning or serving efficiently, based on the map  2715   f  obtained from the server  2715   e.    
     The reception device  2715   b  indicates the cleaning area or the moving destination to the robot  2715   a  or operates an electronic device in the pointing direction of the reception device, based on the map  2715   f  obtained from the server  2715   e.    
     (Electronic Device State Obtainment and Operation) 
       FIG. 91  is a diagram illustrating a situation of electronic device state obtainment and operation. 
     A communication device  2716   a  converts control information to a light emission pattern, and causes a light emitting unit to emit light to a light receiving unit  2716   d  of an electronic device  2716   b.    
     The electronic device  2716   b  reads the control information from the light emission pattern, and operates according to the control information. Upon light reception by the light receiving unit  2716   d , the electronic device  2716   b  converts information indicating the state of the electronic device to a light emission pattern, and causes a light emitting unit  2716   c  to emit light. Moreover, in the case where there is information to be notified to the user such as when the operation ends or when an error occurs, the electronic device  2716   b  converts the information to a light emission pattern and causes the light emitting unit  2716   c  to emit light. 
     The communication device  2716   a  captures the image of the light emitting unit  2716   c , and obtains the transmitted signal. 
     (Electronic Device Recognition) 
       FIG. 92  is a diagram illustrating a situation of recognizing a captured electronic device. 
     A communication device  2717   a  has communication paths to an electronic device  2717   b  and an electronic device  2717   e , and transmits an ID display instruction to each electronic device. 
     The electronic device  2717   b  receives the ID display instruction, and transmits an ID signal using a light emission pattern of a light emitting unit  2717   c.    
     The electronic device  2717   e  receives the ID display instruction, and transmits an ID signal using a position pattern with light emitting units  2717   f ,  2717   g ,  2717   h , and  2717   i.    
     Here, the ID signal transmitted from each electronic device may be an ID held in the electronic device or the details of indication by the communication device  2717   a.    
     The communication device  2717   a  recognizes the captured electronic device and the position relation between the electronic device and the reception device, from the light emission pattern or the position pattern of the light emitting unit(s) in the captured image. 
     Note that the electronic device desirably includes three or more light emitting units to enable the recognition of the position relation between the electronic device and the reception device. 
     (Augmented Reality Object Display) 
       FIG. 93  is a diagram illustrating a situation of displaying an augmented reality (AR) object. 
     A stage  2718   e  for augmented reality display is a light emission pattern or a position pattern of light emitting units  2718   a ,  2718   b ,  2718   c , and  2718   d , to transmit information of the augmented reality object and a reference position for displaying the augmented reality object. 
     A reception device superimposes an augmented reality object  2718   f  on a captured image and displays it, based on the received information. 
     (User Interface) 
     In the case where the light emitting unit is not within the center area of the imaging range, such display that prompts the user to point the center of the imaging range to the light emitting unit is made in order to point the center of the imaging range to the light emitting unit, as illustrated in  FIG. 94 . 
     In the case where the light emitting unit is not within the center area of the imaging range, such display that prompts the user to point the center of the imaging range to the light emitting unit is made in order to point the center of the imaging range to the light emitting unit, as illustrated in  FIG. 95 . 
     Even when the light emitting unit is not recognized within the imaging range, if the position of the light emitting unit can be estimated from the previous imaging result or the information of the 9-axis sensor, gyroscope, microphone, position sensor, and the like equipped in the imaging terminal, such display that prompts the user to point the center of the imaging range to the light emitting unit is made as illustrated in  FIG. 96 . 
     To point the center of the imaging range to the light emitting unit, the size of a figure displayed according to the moving distance of the imaging range is adjusted as illustrated in  FIG. 97 . 
     In the case where the light emitting unit is captured small, such display that prompts the user to get closer to the light emitting unit to capture the image is made in order to capture the light emitting unit larger, as illustrated in  FIG. 98 . 
     In the case where the light emitting unit is not within the center of the imaging range and also the light emitting unit is not captured in a sufficiently large size, such display that prompts the user to point the center of the imaging range to the light emitting unit and also prompts the user to get closer to the light emitting unit to capture the image is made as illustrated in  FIG. 99 . 
     In the case where the signal of the light emitting unit can be more easily received by changing the angle between the light emitting unit and the imaging range, such display that prompts the user to rotate the imaging range is made as illustrated in  FIG. 100 . 
     In the case where the light emitting unit is not within the center of the imaging range and also the signal of the light emitting unit can be more easily received by changing the angle between the light emitting unit and the imaging range, such display that prompts the user to point the center of the imaging range to the light emitting unit and also prompts the user to rotate the imaging range is made as illustrated in  FIG. 101 . 
     In the case where the light emitting unit is not captured in a sufficiently large size and also the signal of the light emitting unit can be more easily received by changing the angle between the light emitting unit and the imaging range, such display that prompts the user to get closer to the light emitting unit to capture the image and also prompts the user to rotate the imaging range is made as illustrated in  FIG. 102 . 
     In the case where the light emitting unit is not within the center of the imaging range, the light emitting unit is not captured in a sufficiently large size, and also the signal of the light emitting unit can be more easily received by changing the angle between the light emitting unit and the imaging range, such display that prompts the user to point the center of the imaging range to the light emitting unit, prompts the user to get closer to the light emitting unit to capture the image, and also prompts the user to rotate the imaging range is made as illustrated in  FIG. 103 . 
     During signal reception, information that the signal is being received and the information amount of the received signal are displayed as illustrated in  FIG. 104 . 
     In the case where the size of the signal to be received is known, during signal reception, the proportion of the signal the reception of which has been completed and the information amount are displayed with a progress bar, as illustrated in  FIG. 105 . 
     During signal reception, the proportion of the signal the reception of which has been completed, the received parts, and the information amount of the received signal are displayed with a progress bar, as illustrated in  FIG. 106 . 
     During signal reception, the proportion of the signal the reception of which has been completed and the information amount are displayed so as to superimpose on a light emitting unit, as illustrated in  FIG. 107 . 
     In the case where a light emitting unit is detected, information that the object is a light emitting unit is displayed by, for example, displaying the light emitting unit as blinking, as illustrated in  FIG. 108 . 
     While receiving a signal from a light emitting unit, information that the signal is being received from the light emitting unit is displayed by, for example, displaying the light emitting unit as blinking, as illustrated in  FIG. 109 . 
     In  FIG. 110 , in the case where a plurality of light emitting units are detected, the user is prompted to designate a transmission device from which a signal is to be received or which is to be operated, by tapping any of the plurality of light emitting units. 
     Embodiment 4 
     (Application to ITS) 
     The following describes ITS (Intelligent Transport Systems) as an example of application of the present disclosure. In this embodiment, high-speed communication of visible light communication is realized, which is adaptable to the field of ITS. 
       FIG. 111  is a diagram for describing communication between a transport system having the visible light communication function and a vehicle or a pedestrian. A traffic light  6003  has the visible light communication function according to this embodiment, and is capable of communicating with a vehicle  6001  and a pedestrian  6002 . 
     Information transmission from the vehicle  6001  or the pedestrian  6002  to the traffic light  6003  is performed using, for example, a headlight or a flash light emitting unit of a mobile terminal carried by the pedestrian. Information transmission from the traffic light  6003  to the vehicle  6001  or the pedestrian  6002  is performed by signal illumination using a camera sensor of the traffic light  6003  or a camera sensor of the vehicle  6001 . 
     The function of communication between a traffic assistance object disposed on the road, such as a road lighting or a road information board, and the vehicle  6001  or the pedestrian  6002  is also described below. Here, since the communication method is the same, the description of other objects is omitted. 
     As illustrated in  FIG. 111 , the traffic light  6003  provides road traffic information to the vehicle  6001 . The road traffic information mentioned here is information for helping driving, such as congestion information, accident information, and nearby service area information. 
     The traffic light  6003  includes an LED lighting. Communication using this LED lighting enables information to be provided to the vehicle  6001  with no need for addition of a new device. Since the vehicle  6001  usually moves at high speed, only a small amount of data can be transmitted in conventional visible light communication techniques. However, the improvement in communication speed according to this embodiment produces an advantageous effect that a larger size of data can be transmitted to the vehicle. 
     Moreover, the traffic light  6003  or a lighting  6004  is capable of providing different information depending on signal or light. It is therefore possible to transmit information according to the vehicle position, such as transmitting information only to each vehicle running in a right turn lane. 
     Regarding the pedestrian  6002 , too, it is possible to provide information only to each pedestrian  6002  at a specific spot. For example, only each pedestrian waiting at a crosswalk signal at a specific intersection may be provided with information that the intersection is accident-prone, city spot information, and the like. 
     The traffic light  6003  is also capable of communicating with another traffic light  6005 . For example, in the case of changing information provided from the traffic light  6003 , the information distributed from the traffic light can be changed through communication relay between traffic lights, with there being no need to newly connecting a signal line or a communication device to the traffic light. According to the method of this embodiment, the communication speed of visible light communication can be significantly improved, so that the distribution information can be changed in a shorter time. This allows the distribution information to be changed several times a day, as an example. Besides, snow information, rain information, and the like can be distributed immediately. 
     Furthermore, the lighting may distribute the current position information to provide the position information to the vehicle  6001  or the pedestrian  6002 . In facilities with roofs such as a shopping arcade and a tunnel, it is often difficult to obtain position information using a GPS. However, the use of visible light communication has an advantageous effect that the position information can be obtained even in such a situation. In addition, since the communication speed can be increased according to this embodiment as compared with conventional techniques, for example it is possible to receive information while passing a specific spot such as a store or an intersection. 
     Note that this embodiment provides speedups in visible light communication, and so is equally applicable to all other ITS systems using visible light communication. 
       FIG. 112  is a schematic diagram of the case of applying the present disclosure to inter-vehicle communication where vehicles communicate with each other using visible light communication. 
     The vehicle  6001  transmits information to a vehicle  6001   a  behind, through a brake lamp or other LED light. The vehicle  6001  may also transmit data to an oncoming vehicle  6001   b , through a headlight or other front light. 
     By communicating between vehicles using visible light in this way, the vehicles can share their information with each other. For instance, congestion information or warning information may be provided to the vehicle behind by relay transmission of information of an accident at an intersection ahead. 
     Likewise, information for helping driving may be provided to the oncoming vehicle by transmitting congestion information or sudden braking information obtained from sensor information of the brake. 
     Since the communication speed of visible light communication is improved according to the present disclosure, there is an advantageous effect that information can be transmitted while passing the oncoming vehicle. Regarding the vehicle behind, too, information can be transmitted to many vehicles in a shorter time because the information transmission interval is shorter. The increase in communication speed also enables transmission of sound or image information. Hence, richer information can be shared among vehicles. 
     (Position Information Reporting System and Facility System) 
       FIG. 113  is a schematic diagram of a position information reporting system and a facility system using the visible light communication technique according to this embodiment. A system of delivering patient medical records, transported articles, drugs, and the like by a robot inside a hospital is described as a typical example. 
     A robot  6101  has the visible light communication function. A lighting distributes position information. The robot  6101  obtains the position information of the lighting, with it being possible to deliver drugs or other items to a specific hospital room. This alleviates burdens on doctors. Since the light never leaks to an adjacent room, there is also an advantageous effect that the robot  6101  is kept from going to the wrong room. 
     The system using visible light communication according to this embodiment is not limited to hospitals, and is adaptable to any system that distributes position information using lighting equipment. Examples of this include: a mechanism of transmitting position and guidance information from a lighting of an information board in an indoor shopping mall; and an application to cart movement in an airport. 
     Moreover, by providing a shop lighting with the visible light communication technique, it is possible to distribute coupon information or sale information. When the information is superimposed on visible light, the user intuitively understands that he or she is receiving the information from the light of the shop. This has an advantageous effect of enhancing user convenience. 
     In the case of transmitting information in or outside a room, if position information is distributed using a wireless LAN, radio waves leak to an adjacent room or corridor, so that a function of blocking radio waves by the outer wall to prevent radio waves from leaking out of the room is needed. Such blocking radio waves by the outer wall causes a problem that any device communicating with the outside, such as a mobile phone, is unusable. 
     When transmitting position information using visible light communication according to this embodiment, the communication can be confined within the reach of light. This has an advantageous effect that, for example, position information of a specific room can be easily transmitted to the user. There is also an advantageous effect that no special device is needed because normally light is blocked by the outer wall. 
     In addition, since the positions of lightings are usually unchanged in buildings, large-scale facilities, and ordinary houses, the position information transmitted by each lighting does not change frequently. The frequency of updating a database of the position information of each lighting is low. This has an advantageous effect that the maintenance cost in position information management is low. 
     (Supermarket System) 
       FIG. 114  illustrates a supermarket system in which, in a store, a device capable of the communication method according to this embodiment is mounted on a shopping cart to obtain position information from a shelf lighting or an indoor lighting. 
     A cart  6201  carries a visible light communication device that uses the communication method according to this embodiment. A lighting  6100  distributes position information and shelf information by visible light communication. The cart can receive product information distributed from the lighting. The cart can also receive the position information to thereby recognize at which shelf the cart is situated. For example, by storing shelf position information in the cart, the direction can be displayed on the cart when the user designates, to the cart, to which shelf he or she wants to go or which product he or she wants to buy. 
     Visible light communication enables obtainment of such accurate position information that makes the shelf positions known, so that the movement information of the cart can be obtained and utilized. For example, a database of position information obtained by the cart from each lighting may be created. 
     The information from the lighting, together with cart information, is transmitted using visible light communication, or transmitted to a server using a wireless LAN or the like. Alternatively, a memory is equipped in the cart, and data is collected after the store is closed to compile, in the server, which path each cart has taken. 
     By collecting the cart movement information, it is possible to recognize which shelf is popular and which aisle is passed most. This has an advantageous effect of being applicable to marketing. 
     (Communication Between Mobile Phone Terminal and Camera) 
       FIG. 115  illustrates an example of application of using visible light communication according to this embodiment. 
     A mobile phone terminal  6301  transmits data to a camera  6302  using a flash. The camera  6302  receives the data transmitted from the mobile phone terminal  6301 , from light information received by an imaging unit. 
     Camera imaging settings are stored in the mobile phone terminal  6301  beforehand, and setting information is transmitted to the camera  6302 . Thus, the camera can be set using rich user interfaces of the mobile phone terminal. 
     Moreover, the use of the image sensor of the camera enables the setting information to be transmitted from the mobile phone terminal to the camera upon communication between the camera and the mobile phone terminal, with there being no need to provide a new communication device such as a wireless LAN. 
     (Underwater Communication) 
       FIG. 116  is a schematic diagram of the case of adapting the communication method according to this embodiment to underwater communication. Since radio waves do not penetrate water, divers underwater or a ship on the sea and a ship in the sea cannot communicate with each other by radio. Visible light communication according to this embodiment, on the other hand, is available even underwater. 
     In the visible light communication method according to this embodiment, data can be transmitted from an object or building emitting light. By pointing a light receiving unit to a building, it is possible to obtain guidance information or detailed information of the building. This allows useful information to be provided to tourists. 
     The visible light communication method according to this embodiment is also applicable to communication from a lighthouse to a ship. More detailed information can be transferred because a larger amount of communication than in conventional techniques is possible. 
     Since light is used in visible light communication according to this embodiment, communication control on a room basis such as communicating only in a specific room can be carried out. As an example, the communication method according to this embodiment may be applied to the case of accessing information available only in a specific room in a library. As another example, the communication method according to this embodiment may be used for exchange of key information, while communication such as a wireless LAN is used for actual communication. 
     Note that the communication method according to this embodiment can be used for all imaging devices having MOS sensors and LED communication, and are applicable to digital cameras, smartphones, and so on. 
     Embodiment 5 
     (Service Provision Example) 
     This embodiment describes an example of service provision to a user as an example of application of the present disclosure, with reference to  FIG. 117 .  FIG. 117  is a diagram for describing an example of service provision to a user in Embodiment 5. A network server  4000   a , transmitters  4000   b ,  4000   d , and  4000   e , receivers  4000   c  and  4000   f , and a building  4000   g  are illustrated in  FIG. 117 . 
     The receivers  4000   c  and  4000   f  receive signals from the plurality of transmitters  4000   b ,  4000   d , and  4000   e  in or outside the house and process the received signals, and can thereby provide services to the user. Here, the transmitters and the receivers may process the signals individually to provide the services to the user, or provide the services to the user while changing their behaviors or transmitted signals according to instructions from a network in cooperation with the network server  4000   a  forming the network. 
     Note that the transmitters and the receivers may be equipped in mobile objects such as vehicles or persons, equipped in stationary objects, or later equipped in existing objects. 
       FIG. 118  is a diagram for describing an example of service provision to a user in Embodiment 5. Transmitters  4001   a  and a receiver  4001   b  are illustrated in  FIG. 118 . 
     As illustrated in  FIG. 118 , the receiver  4001   b  receives signals transmitted from the plurality of transmitters  4001   a  and processes information included in the signals, thereby providing services to the user. The information included in the signals are information relating to: devices IDs uniquely identifying devices; position information; maps; signs; tourist information; traffic information; regional services; coupons; advertisements; product description; characters; music; video; photos; sounds; menus; broadcasting; emergency guidance; time tables; guides; applications; news; bulletin boards; commands to devices; information identifying individuals; vouchers; credit cards; security; and URLs, for example. 
     The user may perform a registration process or the like for using the information included in the signals on a network server beforehand so that the user can be provided with services by receiving the signals by the receiver  4001   b  at the place where the transmitters  4001   a  transmit the signals. Alternatively, the user may be provided with services without via the network server. 
       FIG. 119  is a flowchart illustrating the case where the receiver simultaneously processes the plurality of signals received from the transmitters in this embodiment. 
     First, the procedure starts in Step  4002   a . Next, in Step  4002   b , the receiver receives the signals from the plurality of light sources. Next, in Step  4002   c , the receiver determines the area in which each light source is displayed from the reception result, and extracts the signal from each area. 
     In Step  4002   e , the receiver repeatedly performs a process based on information included in the signal for the number of obtained signals until the number of signals to be processed reaches 0 in Step  4002   d . When the number of signals to be processed reaches 0, the procedure ends in Step  4002   f.    
       FIG. 120  is a diagram illustrating an example of the case of realizing inter-device communication by two-way communication in Embodiment 5. An example of the case of realizing inter-device communication by two-way communication between a plurality of transmitter-receivers  4003   a ,  4003   b , and  4003   c  each including a transmitter and a receiver is illustrated in  FIG. 118 . Note that the transmitter-receivers may be capable of communication between the same devices as in  FIG. 118 , or communication between different devices. 
     Moreover, in this embodiment, the user can be provided with services in such a manner that applications are distributed to a mobile phone, a smartphone, a personal computer, a game machine, or the like using the communication means in this embodiment or other networks or removable storages and already equipped devices (LED, photodiode, image sensor) are used from the applications. Here, the applications may be installed in the device beforehand. 
     (Example of Service Using Directivity) 
     A service using directivity characteristics in this embodiment is described below, as an example of application of the present disclosure. In detail, this is an example of the case of using the present disclosure in public facilities such as a movie theater, a concert hall, a museum, a hospital, a community center, a school, a company, a shopping arcade, a department store, a government office, and a food shop. The present disclosure achieves lowering of directivity of a signal transmitted from a transmitter to a receiver as compared with conventional visible light communication, so that information can be simultaneously transmitted to many receivers present in a public facility. 
       FIG. 121  is a diagram for describing a service using directivity characteristics in Embodiment 5. A screen  4004   a , a receiver  4004   b , and a lighting  4004   c  are illustrated in  FIG. 121 . 
     As illustrated in  FIG. 121 , the application of this embodiment to the movie theater can suppress a situation where, during a movie, the user uses such a device (mobile phone, smartphone, personal computer, game machine, etc.) that interferes with the other users enjoying the movie. The transmitter uses, as a signal, video projected on the screen  4004   a  displaying the movie or light emitted from the lighting  4004   c  disposed in the facility, and includes a command for controlling the receiver  4004   b  in the signal. By the receiver  4004   b  receiving the command, it is possible to control the operation of the receiver  4004   b  to prevent any act that interferes with the other users watching the movie. The command for controlling the receiver  4004   b  relates to power or reception sound, communication function, LED display, vibration ON/OFF, level adjustment, and the like. 
     Moreover, the strength of directivity can be controlled by the receiver filtering the signal from the transmitter through the use of the intensity of the light source and the like. In this embodiment, the command or information can be simultaneously transmitted to the receivers present in the facility, by setting low directivity. 
     In the case of increasing the directivity, the constraint may be imposed by the transmitter limiting the amount of light source or the receiver reducing the sensitivity of receiving the light source or performing signal processing on the received light source amount. 
     In the case where this embodiment is applied to a store where the user&#39;s order is received and processed at the place, such as a food shop or a government office, a signal including the order transmitted from a transmitter held by the user is received by a receiver placed at such a position that can overlook the store, so that which menu is ordered by the user of which seat can be detected. The service provider processes the order on a time axis, with it being possible to provide the service of high fairness to the user. 
     Here, a secret key or a public key preset between the transmitter and the receiver may be used to encrypt/decrypt the information included in the signal, to thereby restrict transmitters capable of signal transmission and receivers capable of signal reception. Moreover, a protocol such as SSL used in the Internet by default may be employed for a transmission path between the transmitter and the receiver, to prevent signal interception by other devices. 
     (Service Example by Combination of Real World and Internet World) 
     The following describes a service provided to a user by superimposing of information of the real world captured by a camera and the Internet world, as an example of application of the present disclosure. 
       FIG. 122  is a diagram for describing another example of service provision to a user in Embodiment 5. In detail,  FIG. 122  illustrates an example of a service in the case of applying this embodiment using a camera  4005   a  equipped in a receiver such as a mobile phone, a smartphone, or a game machine. The camera  4005   a , light sources  4005   b , and superimposition information  4005   c  are illustrated in  FIG. 122 . 
     Signals  4005   d  transmitted from the plurality of light sources  4005   b  are extracted from the imaging result of the camera  4005   a , and information included in the signals  4005   d  is superimposed on the camera  4005   a  and displayed. Examples of the superimposition information  4005   c  to be superimposed on the camera  4005   a  include character strings, images, video, characters, applications, and URLs. Note that the information included in the signals may be processed not only by superimposition on the camera but also by use of sounds, vibrations, or the like. 
       FIG. 123  is a diagram illustrating a format example of a signal included in a light source emitted from a transmitter. Light source characteristics  4006   a , a service type  4006   b , and service-related information  4006   c  are illustrated in  FIG. 123 . 
     The information  4006   c  related to the service of superimposing the signal received by the receiver on the camera is the result of filtering the information obtainable from the signal according to the information such as the service type  4006   b  included in the signal transmitted from the transmitter and the distance from the camera to the light source. The information to be filtered by the receiver may be determined according to settings made in the receiver beforehand or user preference set in the receiver by the user. 
     The receiver can estimate the distance to the transmitter transmitting the signal, and display the distance to the light source. The receiver estimates the distance to the transmitter, by performing digital signal processing on the intensity of light emitted from the transmitter captured by the camera. 
     However, since the intensity of light of each transmitter captured by the camera of the receiver is different depending on the position or strength of the light source, significant deviation may be caused if the distance is estimated only by the intensity of light of the captured transmitter. 
     To solve this, the light source characteristics  4006   a  indicating the intensity, color, type, and the like of the light source are included in the signal transmitted from the transmitter. By performing digital signal processing while taking into account the light source characteristics included in the signal, the receiver can estimate the distance with high accuracy. In the case where a plurality of light sources are captured by the receiver, if all light sources have the same intensity, the distance is estimated using the intensity of light of the light source. If there is a transmitter of different intensity out of the light sources captured by the receiver, the distance from the transmitter to the receiver is estimated by not only using the light source amount but also using other distance measurement means in combination. 
     As the other distance measurement means, the distance may be estimated by using the parallax in image captured by a twin-lens camera, by using an infrared or millimeter wave radar, or by obtaining the moving amount of the receiver by a 9-axis sensor or an image sensor in the receiver and combining the moving distance with triangulation. 
     Note that the receiver may not only filter and display the signal using the strength or distance of the signal transmitted from the transmitter, but also adjust the directivity of the signal received from the transmitter. 
     Embodiment 6 
     The following is a description of the flow of processing of communication performed using a camera of a smartphone by transmitting information using a blink pattern of an LED included in a device. 
       FIG. 124  is a diagram illustrating an example of the environment in a house in the present embodiment. In the environment illustrated in  FIG. 124 , there are a television  1101 , a microwave  1106 , and an air cleaner  1107 , in addition to a smartphone  1105 , for instance, around a user. 
       FIG. 125  is a diagram illustrating an example of communication between the smartphone and the home electric appliances according to the present embodiment.  FIG. 125  illustrates an example of information communication, and is a diagram illustrating a configuration in which information output by devices such as the television  1101  and the microwave  1106  in  FIG. 124  is obtained by a smartphone  1201  owned by a user, thereby obtaining information. As illustrated in  FIG. 125 , the devices transmit information using LED blink patterns, and the smartphone  1201  receives the information using an image pickup function of a camera, for instance. 
       FIG. 126  is a diagram illustrating an example of a configuration of a transmitter device  1301  according to the present embodiment. 
     The transmitter device  1301  transmits information using light blink patterns by pressing a button by a user, transmitting a transmission instruction using, for instance, near field communication (NFC), and detecting a change in a state such as failure inside the device. At this time, transmission is repeated for a certain period of time. A simplified identification (ID) may be used for transmitting information to a device which is registered previously. In addition, if a device has a wireless communication unit which uses a wireless LAN and specific power-saving wireless communication, authentication information necessary for connection thereof can also be transmitted using blink patterns. 
     In addition, a transmission speed determination unit  1309  ascertains the performance of a clock generation device inside a device, thereby performing processing of decreasing the transmission speed if the clock generation device is inexpensive and does not operate accurately and increasing the transmission speed if the clock generation device operates accurately. Alternatively, if a clock generation device exhibits poor performance, it is also possible to reduce an error due to the accumulation of differences of blink intervals because of a long-term communication, by dividing information to be transmitted itself into short pieces. 
       FIG. 127  illustrates an example of a configuration of a receiver device  1401  according to the present embodiment. 
     The receiver device  1401  determines an area where light blink is observed, from a frame image obtained by an image obtaining unit  1404 . At this time, for the blink, it is also possible to take a method of tracking an area where an increase or a decrease in brightness by a certain amount is observed. 
     A blink information obtaining unit  1406  obtains transmitted information from a blink pattern, and if the information includes information related to a device such as a device ID, an inquiry is made as to information on a related server on a cloud computing system using the information, or interpolation is performed using information stored previously in a device in a wireless-communication area or information stored in the receiver apparatus. This achieves advantageous effect of reducing a time for correcting error due to noise when capturing a light emission pattern or for a user to hold up a smartphone to the light-emitting part of the transmitter device to obtain information already acquired. 
     The following is a description of  FIG. 128 . 
       FIG. 128  is a diagram illustrating a flow of processing of transmitting information to a receiver device such as a smartphone by blinking an LED of a transmitter device according to the present embodiment. Here, a state is assumed in which a transmitter device has a function of communicating with a smartphone by NFC, and information is transmitted with a light emission pattern of the LED embedded in part of a communication mark for NFC which the transmitter device has. 
     First, in step  1001   a , a user purchases a home electric appliance, and connects the appliance to power supply for the first time, thereby causing the appliance to be in an energized state. 
     Next, in step  1001   b , it is checked whether initial setting information has been written. In the case of Yes, the processing proceeds to C in  FIG. 128 . In the case of No, the processing proceeds to step  1001   c , where the mark blinks at a blink speed (for example: 1 to ⅖) which the user can easily recognize. 
     Next, in step  1001   d , the user checks whether device information of the home electric appliance is obtained by bringing the smartphone to touch the mark via NFC communication. Here, in the case of Yes, the processing proceeds to step  1001   e , where the smartphone receives device information to a server of the cloud computing system, and registers the device information at the cloud computing system. Next, in step  1001   f , a simplified ID associated with an account of the user of the smartphone is received from the cloud computing system and transmitted to the home electric appliance, and the processing proceeds to step  1001   g . It should be noted that in the case of No in step  1001   d , the processing proceeds to step  1001   g.    
     Next, in step  1001   g , it is checked whether there is registration via NFC. In the case of Yes, the processing proceeds to step  1001   j , where two blue blinks are made, and thereafter the blinking stops in step  1001   k.    
     In the case of No in step  1001   g , the processing proceeds to step  1001   h . Next, it is checked in step  1001   h  whether 30 seconds have elapsed. Here, in the case of Yes, the processing proceeds to step  1001   i , where an LED portion outputs device information (a model number of the device, whether registration processing has been performed via NFC, an ID unique to the device) by blinking light, and the processing proceeds B in  FIG. 129 . 
     It should be noted that in the case of No in step  1001   h , the processing returns to step  1001   d.    
     Next, a description is given of, using  FIGS. 129 to 132 , a flow of processing of transmitting information to a receiver device by blinking an LED of a transmitter device according to the present embodiment. Here,  FIGS. 129 to 132  are diagrams illustrating a flow of processing of transmitting information to a receiver device by blinking an LED of a transmitter apparatus. 
     The following is a description of  FIG. 129 . 
     First, the user activates an application for obtaining light blink information of the smartphone in step  1002   a.    
     Next, the image obtaining portion obtains blinks of light in step  1002   b . Then, a blinking area determination unit determines a blinking area from a time series change of an image. 
     Next, in step  1002   c , a blink information obtaining unit determines a blink pattern of the blinking area, and waits for detection of a preamble. 
     Next, in step  1002   d , if a preamble is successfully detected, information on the blinking area is obtained. 
     Next, in step  1002   e , if information on a device ID is successfully obtained, also in a reception continuing state, Information is transmitted to a server of the cloud computing system, an information interpolation unit performs interpolation while comparing information acquired from the cloud computing system to information obtained by the blink information obtaining unit. 
     Next, in step  1002   f , when all the information including information as a result of the interpolation is obtained, the smartphone or the user is notified thereof. At this time, a GUI and a related site acquired from the cloud computing system are displayed, thereby allowing the notification to include more information and be readily understood, and the processing proceeds to D in  FIG. 130   
     The following is a description of  FIG. 130 . 
     First, in step  1003   a , an information transmission mode is started when a home electric appliance creates a message indicating failure, a usage count to be notified to the user, and a room temperature, for instance. 
     Next, the mark is caused to blink per 1 to 2 seconds in step  1003   b . Simultaneously, the LED also starts transmitting information. 
     Next, in step  1003   c , it is checked whether communication via NFC has been started. It should be noted that in the case of No, the processing proceeds to G in  FIG. 132 . In the case of Yes, the processing proceeds to step  1003   d , where blinking the LED is stopped. 
     Next, the smartphone accesses the server of the cloud computing system and displays related information in step  1003   e.    
     Next, in step  1003   f , in the case of failure which needs to be handled at the actual location, a serviceman who gives support is looked for by the server. Information on the home electric appliance, a setting position, and the location are utilized. 
     Next, in step  1003   g , the serviceman sets the mode of the device to a support mode by pressing buttons of the home electric appliance in the predetermined order. 
     Next, in step  1003   h , if blinks of a marker for an LED of a home electric appliance other than the home electric appliance of interest can be seen from the smartphone, some of or all such LEDs observed simultaneously blink so as to interpolate Information, and the processing proceeds to E in  FIG. 131 . 
     The following is a description of  FIG. 131 . 
     First, in step  1004   a , the serviceman-presses a setting button of his/her receiving terminal if the performance of the terminal allows detection of blinking at a high speed (for example, 1000 times/second). 
     Next, in step  1004   b , the LED of the home electric appliance blinks in a high speed mode, and the processing proceeds to F. 
     The following is a description of  FIG. 132 . 
     First, the blinking is continued in step  1005   a.    
     Next, in step  1005   b , the user obtains, using the smartphone, blink information of the LED. 
     Next, the user activates an application for obtaining light blinking information of the smartphone in step  1005   c.    
     Next, the image obtaining portion obtains the blinking of light in step  1005   d . Then, the blinking area determination unit determines a blinking area, from a time series change in an image. 
     Next, in step  1005   e , the blink information obtaining unit determines a blink pattern of the blinking area, and waits for detection of a preamble. 
     Next, in step  1005   f , if a preamble is successfully detected, information on the blinking area is obtained. 
     Next, in step  1005   g , if information on a device ID is successfully obtained, also in a reception continuing state, information is transmitted to the server of the cloud computing system, and the information interpolation unit performs interpolation while comparing information acquired from the cloud computing system with information obtained by the blink information obtaining unit. 
     Next, in step  1005   h , if all the information pieces including information as a result of the interpolation are obtained, the smartphone or the user is notified thereof. At this time, a GUI and a related site acquired from the cloud computing system are displayed, thereby allowing the notification to be include more information and easier to understand. 
     Then, the processing proceeds to step  1003   f  in  FIG. 130 . 
     In this manner, a transmission device such as a home electric appliance can transmit information to a smartphone by blinking an LED. Even a device which does not have means of communication such as wireless communication function or NFC can transmit information, and provide a user with information having a lot of details which is in the server of the cloud computing system via a smartphone. 
     Moreover, as described in this embodiment, consider a situation where two devices including at least one mobile device are capable of transmitting and receiving data by both communication methods of bidirectional communication (e.g. communication by NFC) and unidirectional communication (e.g. communication by LED luminance change). In the case where data transmission and reception by bidirectional communication are established when data is being transmitted from one device to the other device by unidirectional communication, unidirectional communication can be stopped. This benefits efficiency because power consumption necessary for unidirectional communication is saved. 
     As described above, according to Embodiment 6, an information communication device can be achieved which allows communication between various devices including a device which exhibits low computational performance. 
     Specifically, an information communication device according to the present embodiment includes: an information management unit configured to manage device information which includes an ID unique to the information communication device and state information of a device; a light emitting element; and a light transmission unit configured to transmit information using a blink pattern of the light emitting element, wherein when an internal state of the device has changed, the light transmission unit is configured to convert the device information into the blink pattern of the light emitting element, and transmit the converted device information. 
     Here, for example, the device may further include an activation history management unit configured to store information sensed in the device including an activation state of the device and a user usage history, wherein the light transmission unit is configured to obtain previously registered performance information of a clock generation device to be utilized, and change a transmission speed. 
     In addition, for example, the light transmission unit may include a second light emitting element disposed in vicinity of a first light emitting element for transmitting information by blinking, and when information transmission is repeatedly performed a certain number of times by the first light emitting element blinking, the second light emitting element may emit light during an interval between an end of the information transmission and a start of the information transmission. 
     It should be noted that these general and specific embodiments may be implemented using a system, a method, an integrated circuit, a computer program, or a recording medium, or any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     Embodiment 7 
     In the present embodiment, a description is given, using a cleaner as an example, of the procedure of communication between a device and a user using visible light communication, initial settings to a repair service at the time of failure using visible light communication, and service cooperation using the cleaner. 
       FIGS. 133 and 134  are diagrams for describing the procedure of performing communication between a user and a device using visible light according to the present embodiment. 
     The following is a description of  FIG. 133 . 
     First, the processing starts from A. 
     Next, the user turns on a device in step  2001   a.    
     Next, in step  2001   b , as start processing, it is checked whether initial settings such as installation setting and network (NW) setting have been made. 
     Here, if initial settings have been made, the processing proceeds to step  2001   f , where normal operation starts, and the processing ends as illustrated by C. 
     If initial settings have not been made, the processing proceeds to step  2001   c , where “LED normal light emission” and an “audible tone” notify the user that initial settings need to be made. 
     Next, in step  2001   d , device information (product number and serial number) is collected, and visible light communication is prepared. 
     Next, in step  2001   e , “LED communication light emission”, “icon display on the display”, “audible tone”, and “light emission by plural LEDs” notify the user that device information (product number and serial number) can be transmitted by visible light communication. 
     Then, the processing ends as illustrated by B. 
     Next is a description of  FIG. 134 . 
     First, the processing starts as illustrated by B. 
     Next, in step  2002   a , the approach of a visible light receiving terminal is perceived by a “proximity sensor”, an “Illuminance sensor”, and a “human sensing sensor”. 
     Next, in step  2002   b , visible light communication is started by the perception thereof which is a trigger. 
     Next, in step  2002   c , the user obtains device information using the visible light receiving terminal. 
     Next, the processing ends as illustrated by D. Alternatively, the processing proceeds to one of steps  2002   f  to  2002   i.    
     If the processing proceeds to step  2002   f , it is perceived, by a “sensitivity sensor” and “cooperation with a light control device,” that the light of a room is switched off, and light emission for device information is stopped. The processing ends as illustrated by E. If the processing proceeds to step  2002   g , the visible light receiving terminal notifies, by “NFC communication” and “NW communication”, that device information has been perceived and obtained, and the processing ends. If the processing proceeds to step  2002   h , it is perceived that the visible light receiving terminal has moved away, light emission for device information is stopped, and the processing ends. If the processing proceeds to step  2002   i , after a certain time period elapses, light emission for device information is stopped, and the processing ends. 
     It should be noted that if the approach is not perceived in step  2002   a , the processing proceeds to step  2002   d , where after a certain period of time elapses, the level of notification indicating that visible light communication is possible is increased by “brightening”, “increasing sound volume”, and “moving an icon”, for instance. Here, the processing returns to step  2002   d . Alternatively, the processing proceeds to step  2002   e , and proceeds to step  2002   i  after another certain period of time elapses. 
       FIG. 135  is a diagram for describing a procedure from when the user purchases a device until when the user makes initial settings of the device according to the present embodiment. 
     In  FIG. 135 , first, the processing starts as illustrated by D. 
     Next, in step  2003   a , position information of a smartphone which has received device information is obtained using the global positioning system (GPS). 
     Next, in step  2003   b , if the smartphone has user information such as a user name, a telephone number, and an e-mail address, such user information is collected in the terminal. Alternatively, in step  2003   c , if the smartphone does not have user information, user information is collected from a device in the vicinity via NW. 
     Next, in step  2003   d , device information, user information, and position information are transmitted to the cloud server. 
     Next, in step  2003   e , using the device information and the position information, information necessary for initial settings and activation information are collected. 
     Next, in step  2003   f , cooperation information such as an Internet protocol (IP), an authentication method, and available service necessary for setting cooperation with a device whose user has been registered is collected. Alternatively, in step  2003   g , device information and setting information are transmitted to a device whose user has been registered via NW to make cooperation setting with devices in the vicinity thereof. 
     Next, user setting is made in step  2003   h  using device information and user information. 
     Next, initial setting information, activity information, and cooperation setting information are transmitted to the smartphone in step  2003   i.    
     Next, the initial setting information, the activation information, and the cooperation setting information are transmitted to home electric appliance by NFC in step  2003   j.    
     Next, device setting is made using the initial setting information, the activation information, and the cooperation setting information in step  2003   k.    
     Then, the processing ends as illustrated by F. 
       FIG. 136  is a diagram for describing service exclusively performed by a serviceman when a device fails according to the present embodiment. 
     In  FIG. 136 , first, the processing starts as illustrated by C. 
     Next, in step  2004   a , history information such as operation log and user operation log generated during a normal operation of the device is stored into a local storage medium. 
     Next, in step  2004   b , at the same time with the occurrence of a failure, error information such as an error code and details of the error is recorded, and LED abnormal light emission notifies that visible light communication is possible. 
     Next, in step  2004   c , the mode is changed to a high-speed LED light emission mode by the serviceman executing a special command, thereby starting high-speed visible light communication. 
     Next, in step  2004   d , it is identified whether a terminal which has approached is an ordinary smartphone or a receiving terminal exclusively used by the serviceman. Here, if the processing proceeds to step  2004   e , error information is obtained in the case of a smartphone, and the processing ends. 
     On the other hand, if the processing proceeds to step  2004   f , the receiving terminal for exclusive use obtains error information and history information in the case of a serviceman. 
     Next, in step  2004   g , device information, error information, and history information are transmitted to the cloud computing system, and a repair method is obtained. Here, if the processing proceeds to step  2004   h , the high-speed LED light emission mode is canceled by the serviceman executing a special command, and the processing ends. 
     On the other hand, if the processing proceeds to step  2004   i , product information on products related and similar to the product in the device information, selling prices at nearby stores, and new product information are obtained from the cloud server. 
     Next, in step  2004   j , user information is obtained via visible light communication between the user&#39;s smartphone and the terminal exclusively used by the serviceman, and an order for a product is made to a nearby store via the cloud server. 
     Then, the processing ends as illustrated by I. 
       FIG. 137  is a diagram for describing service for checking a cleaning state using a cleaner and visible light communication according to the present embodiment. 
     First, the processing starts as illustrated by C. 
     Next, cleaning information of a device performing normal operation is recorded in step  2005   a.    
     Next, in step  2005   b , dirt information is created in combination with room arrangement information, and encrypted and compressed. 
     Here, if the processing proceeds to step  2005   c , the dirt information is stored in a local storage medium, which is triggered by compression of the dirt information. Alternatively, if the processing proceeds to step  2005   d , dirt information is transmitted to a lighting device by visible light communication, which is triggered by a temporary stop of cleaning (stoppage of suction processing). Alternatively, if the processing proceeds to step  2005   e , the dirt information is transmitted to a domestic local server and the cloud server via NW, which is triggered by recording dirt information. 
     Next, in step  2005   f , device information, a storage location, and a decryption key are transmitted to the smartphone by visible light communication, which is triggered by the transmission and storage of the dirt information. 
     Next, in step  2005   g , the dirt information is obtained via NW and NFC, and decoded. 
     Then, the processing ends as illustrated by J. 
     As described above, according to Embodiment 7, a visible light communication system can be achieved which includes an information communication device allowing communication between various devices including a device which exhibits low computational performance. 
     Specifically, the visible light communication system ( FIG. 133 ) including the information communication device according to the present embodiment includes a visible light transmission permissibility determination unit for determining whether preparation for visible light transmission is completed, and a visible light transmission notification unit which notifies a user that visible light transmission is being performed, wherein when visible light communication is possible, the user is notified visually and auditorily. Accordingly, the user is notified of a state where visible light reception is possible by an LED light emission mode, such as “emitted light color”, “sound”, “icon display”, or “light emission by a plurality of LEDs”, thereby improving user&#39;s convenience. 
     Preferably, the visible light communication system may include, as described using  FIG. 134 , a terminal approach sensing unit which senses the approach of a visible light receiving terminal, and a visible light transmission determination unit which determines whether visible light transmission is started or stopped, based on the position of a visible light receiving terminal, and may start visible light transmission, which is triggered by the terminal approaching sensing unit sensing the approach of the visible light receiving terminal. 
     Here, as described using  FIG. 134 , for example, the visible light communication system may stop visible light transmission, which is triggered by the terminal approaching sensing unit sensing that the visible light receiving terminal has moved away. In addition, as described using  FIG. 134 , for example, the visible light communication system may include a surrounding illuminance sensing unit which senses that a light of a room is turned off, and may stop visible light transmission, which is triggered by the surrounding illuminance sensing unit sensing that the light of the room is turned off. By sensing that a visible light receiving terminal approaches and moves away and a light of a room is turned off, visible light communication is started only in a state in which visible light communication is possible. Thus, unnecessary visible light communication is not performed, thereby saving energy. 
     Furthermore, as described using  FIG. 134 , for example, the visible light communication system may include: a visible light communication time monitoring unit which measures a time period during which visible light transmission is performed; and a visible light transmission notification unit which notifies a user that visible light transmission is being performed, and may further increase the level of visual and auditory notification to a user, which is triggered by no visible light receiving terminal approaching even though visible light communication is performed more than a certain time period. In addition, as described using  FIG. 134 , for example, the visible light communication system may stop visible light transmission, which is triggered by no visible light receiving terminal approaching even though visible light communication is performed more than a certain time period after the visible light transmission notification unit increases the level of notification. 
     Accordingly, if reception by a user is not performed after a visible light transmission time elapses which is greater than or equal to a certain time period, a request to a user to perform visible light reception and to stop visible light transmission is made to avoid not performing visible light reception and not stopping visible light transmission, thereby improving a user&#39;s convenience. 
     The visible light communication system ( FIG. 135 ) including the information communication device according to the present embodiment may include: a visible light reception determination unit which determines that visible light communication has been received; a receiving terminal position obtaining unit for obtaining a position of a terminal; and a device-setting-information collecting unit which obtains device information and position information to collect device setting information, and may obtain a position of a receiving terminal, which is triggered by the reception of visible light, and collect information necessary for device setting. Accordingly, position information and user information necessary for device setting and user registration are automatically collected and set, which is triggered by device information being obtained via visible light communication, thereby improving convenience by skipping the input and registration procedure by a user. 
     Here, as described using  FIG. 137 , the visible light communication system may further include: a device information management unit which manages device information; a device relationship management unit which manages the similarity between devices; a store information management unit which manages information on a store which sells a device; and a nearby store search unit which searches for a nearby store, based on position information, and may search for a nearby store which sells a similar device and obtain a price thereof, which is triggered by receiving device information and position information. This saves time and effort for collecting information on a selling state of a related device and stores selling such a device according to device information, and searching for a device, thereby improving user convenience. 
     In addition, the visible light communication system ( FIG. 135 ) which includes the information communication device according to the present embodiment may include: a user information monitoring unit which monitors user information being stored in a terminal; a user information collecting unit which collects user information from devices in the vicinity through NW; and a user registration processing unit which obtains user information and device information to register a user, and may collect user information from accessible devices in the vicinity, which is triggered by no user information being obtained, and register a user together with device information. Accordingly, position information and user information necessary for device setting and user registration are automatically collected and set, which is triggered by device information being obtained by visible light communication, thereby improving convenience by skipping the input and a registration procedure by a user. 
     In addition, the visible light communication system ( FIG. 136 ) including the information communication device according to the present embodiment may include: a command determination unit which accepts a special command; and a visible light communication speed adjustment unit which controls the frequency of visible light communication and cooperation of a plurality of LEDs, and may adjust the frequency of visible light communication and the number of transmission LEDs by accepting a special command, thereby accelerating visible light communication. Here, for example, as described using  FIG. 137 , the visible light communication system may include: a terminal type determination unit which identifies the type of an approaching terminal by NFC communication; and a transmission information type determination unit which distinguishes information to be transmitted according to a terminal type, and may change the amount of information to be transmitted and the visible light communication speed according to the terminal which approaches. Thus, according to a receiving terminal, the frequency of visible light communication and the number of transmission LEDs are adjusted to change the speed of the visible light communication and information to be transmitted, thereby allowing high speed communication and improving user&#39;s convenience. 
     In addition, the visible light communication system ( FIG. 137 ) which includes the information communication device according to the present embodiment may include: a cleaning information recording unit which records cleaning information; a room arrangement information recording unit which records room arrangement information; an information combining unit which creates dirty portion information by superimposing the room arrangement information and the cleaning information; and an operation monitoring unit which monitors the stop of normal operation, and may transmit the dirty portion information, using visible light, which is triggered by the perception of the stop of a device. 
     It should be noted that these general and specific embodiments may be implemented using a system, a method, an integrated circuit, a computer program, or a recording medium, or any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     Embodiment 8 
     In the present embodiment, cooperation of devices and Web information using optical communication are described, using a home delivery service as an example. 
     The outline of the present embodiment is illustrated in  FIG. 138 . Specifically,  FIG. 138  is a schematic diagram of home delivery service support using optical communication according to the present embodiment. 
     Specifically, an orderer orders a product from a product purchase site using a mobile terminal  3001   a . When the order is completed, an order number is issued from the product purchase site. The mobile terminal  3001   a  which has received the order number transmits the order number to an intercom indoor unit  3001   b , using NFC communication. 
     The intercom indoor unit  3001   b , for example, displays the order number received from the mobile terminal  3001   a  on the monitor of the unit itself, thereby showing to the user that the transmission has been completed. 
     The intercom indoor unit  3001   b  transmits, to an intercom outdoor unit  3001   c , blink instructions and blink patterns for an LED included in the intercom outdoor unit  3001   c . The blink patterns are created by the intercom indoor unit  3001   b  according to the order number received from the mobile terminal  3001   a.    
     The intercom outdoor unit  3001   c  blinks the LED according to the blink patterns designated by the intercom indoor unit  3001   b.    
     Instead of a mobile terminal, an environment may be used which is accessible to a product purchase site in WWW  3001   d , such as a personal computer (PC). 
     A home network may be used as means for transmission from the mobile terminal  3001   a  to the intercom indoor unit  3001   b , in addition to NFC communication. 
     The mobile terminal  3001   a  may transmit the order number to the intercom outdoor unit  3001   c  directly, not via the intercom indoor unit  3001   b.    
     If there is an order from an orderer, an order number is transmitted from a delivery order receiving server  3001   e  to a deliverer mobile terminal  3001   f . When the deliverer arrives at a delivery place, the deliverer mobile terminal  3001   f  and the intercom outdoor unit  3001   c  bidirectionally perform optical communication using the LED blink patterns created based on the order number. 
     Next, a description is given using  FIGS. 139 to 144 .  FIGS. 139 to 144  are flowcharts for describing home delivery service support using optical communication according to Embodiment 3 of the present disclosure. 
       FIG. 139  illustrates a flow from when an orderer places an order until when an order number is issued. The following is a description of  FIG. 139 . 
     In step  3002   a , the orderer mobile terminal  3001   a  reserves delivery using the web browser or an application of the smartphone. Then, the processing proceeds to A in  FIG. 140 . 
     In step  3002   b  subsequent to B in  FIG. 140 , the orderer mobile terminal  3001   a  waits for the order number to be transmitted. Next, in step  3002   c , the orderer mobile terminal  3001   a  checks whether the terminal has been brought to touch an order number transmission destination device. In the case of Yes, the processing proceeds to step  3002   d , where the order number is transmitted by touching the intercom indoor unit via NFC (if the intercom and the smartphone are in the same network, a method for transmitting the number via the network may also be used). On the other hand, in the case of No, the processing returns to step  3002   b.    
     First, the intercom indoor unit  3001   b  waits for an LED blink request from another terminal in step  3002   e . Next, the order number is received from the smartphone in step  3002   f . Next, the intercom indoor unit  3001   b  gives an instruction to blink an LED of the intercom outdoor unit according to the received order number, in step  3002   g . Then, the processing proceeds to C in  FIG. 142 . 
     First, the intercom outdoor unit  3001   c  waits for the LED blink instruction from the intercom indoor unit in step  3002   h . Then, the processing proceeds to G in  FIG. 142 . 
     In step  30021 , the deliverer mobile terminal  3001   f  waits for an order notification. Next, the deliverer mobile terminal  3001   f  checks whether the order notification has been given from the delivery order server. Here, in the case of No, the processing returns to step  3002   i . In the case of Yes, the processing proceeds to step  3002   k , where the deliverer mobile terminal  3001   f  receives information on an order number, a delivery address, and the like. Next, in step  3002   n , the deliverer mobile terminal  3001   f  waits until its camera is activated to recognize an LED light emission instruction for the order number received by the user and LED light emission from another device. Then, the processing proceeds to E in  FIG. 141 . 
       FIG. 140  illustrates the flow until an orderer makes a delivery order using the orderer mobile terminal  3001   a . The following is a description of  FIG. 140 . 
     First, a delivery order server  3001   e  waits for an order number in step  3003   a . Next, in step  3003   b , the delivery order server  3001   e  checks whether a delivery order has been received. Here, in the case of No, the processing returns to step  3003   a . In the case of Yes, the processing proceeds to step  3003   c , where an order number is issued to the received delivery order. Next, in step  3003   d , the delivery order server  3001   e  notifies a deliverer that the delivery order has been received, and the processing ends. 
     In step  3003   e  subsequent to A in  FIG. 139 , the orderer mobile terminal  3001   a  selects what to order from the menu presented by the delivery order server. Next, in step  3003   f , the orderer mobile terminal  3001   a  sets the order, and transmits the order to the delivery server. Next, the orderer mobile terminal  3001   a  checks in step  3003   g  whether the order number has been received. Here, in the case of No, the processing returns to step  3003   f . In the case of Yes, the processing proceeds to step  3003   h , where the orderer mobile terminal  3001   a  displays the received order number, and prompts the user to touch the intercom indoor unit. Then, the processing proceeds to B in  FIG. 139 . 
       FIG. 141  illustrates the flow of the deliverer performing optical communication with the intercom outdoor unit  3001   c  at a delivery destination, using the deliverer mobile terminal  3001   f . The following is a description of  FIG. 141 . 
     In step  3004   a  subsequent to E in  FIG. 139 , the deliverer mobile terminal  3001   f  checks whether to activate a camera in order to recognize an LED of the intercom outdoor unit  3001   c  at the delivery destination. Here, in the case of No, the processing returns E in  FIG. 139 . 
     On the other hand, in the case of Yes, the processing proceeds to step  3004   b , where the blinks of the LED of the intercom outdoor unit at the delivery destination are identified using the camera of the deliverer mobile terminal. 
     Next, in step  3004   c , the deliverer mobile terminal  3001   f  recognizes light emission of the LED of the intercom outdoor unit, and checks it against the order number. 
     Next, in step  3004   d , the deliverer mobile terminal  3001   f  checks whether the blinks of the LED of the intercom outdoor unit correspond to the order number. Here, in the case of Yes, the processing proceeds to F in  FIG. 143 . 
     It should be noted that in the case of No, the deliverer mobile terminal  3001   f  checks whether the blinks of another LED can be identified using the camera. In the case of Yes, the processing returns to step  3004   c , whereas the processing ends in the case of No. 
       FIG. 142  illustrates the flow of order number checking between the intercom indoor unit  3001   b  and the intercom outdoor unit  3001   c . The following is a description of  FIG. 142 . 
     In step  3005   a  subsequent to G in  FIG. 139 , the intercom outdoor unit  3001   c  checks whether the intercom indoor unit has given an LED blink instruction. In the case of No, the processing returns to G in  FIG. 139 . In the case of Yes, the processing proceeds to step  3005   b , where the intercom outdoor unit  3001  blinks the LED in accordance with the LED blink instruction from the intercom indoor unit. Then, the processing proceeds to H in  FIG. 143 . 
     In step  3005   c  subsequent to I in  FIG. 143 , the intercom outdoor unit  3001   c  notifies the intercom indoor unit of the blinks of the LED recognized using the camera of the intercom outdoor unit. Then, the processing proceeds to J in  FIG. 144 . 
     In step  3005   d  subsequent to C in  FIG. 139 , the intercom indoor unit  3001   c  gives an instruction to the intercom outdoor unit to blink the LED according to the order number. Next, in step  3005   e , the intercom indoor unit  3001   b  waits until the camera of the intercom outdoor unit recognizes the blinks of the LED of the deliverer mobile terminal. Next, in step  3005   f , the intercom indoor unit  3001   b  checks whether the intercom outdoor unit has notified that the blinks of the LED are recognized. Here, in the case of No, the processing returns to step  3005   e . In the case of Yes, the intercom indoor unit  3001   b  checks the blinks of the LED of the intercom outdoor unit against the order number in step  3005   g . Next, in step  3005   h , the intercom indoor unit  3001   b  checks whether the blinks of the LED of the intercom outdoor unit correspond to the order number. In the case of Yes, the processing proceeds to K in  FIG. 144 . On the other hand, in the case of No, the intercom indoor unit  3001   b  gives an instruction to the intercom outdoor unit to stop blinking the LED in step  30051 , and the processing ends. 
       FIG. 143  illustrates the flow between the intercom outdoor unit  3001   c  and the deliverer mobile terminal  3001   f  after checking against the order number. The following is a description of  FIG. 143 . 
     In step  3006   a  subsequent to F in  FIG. 141 , the deliverer mobile terminal  3001   f  starts blinking the LED according to the order number held by the deliverer mobile terminal. 
     Next, in step  3006   b , an LED blinking portion is put in the range from the intercom outdoor unit where the camera can capture an image. 
     Next, in step  3006   c , the deliverer mobile terminal  3001   f  checks whether the blinks of the LED of the intercom outdoor unit indicate that the blinks of the LED of the deliverer mobile terminal shot by the camera of the intercom outdoor unit correspond to the order number held by the intercom indoor unit. 
     Here, in the case of No, the processing returns to step  3006   b . On the other hand, the processing proceeds to step  3006   e  in the case of Yes, where the deliverer mobile terminal displays whether the blinks correspond to the order number, and the processing ends. 
     Furthermore, as illustrated in  FIG. 143 , the intercom outdoor unit  3001   c  checks whether the blinks of the LED of the deliverer mobile terminal have been recognized using the camera of the intercom outdoor unit, in step  3006   f  subsequent to H in  FIG. 142 . Here, in the case of Yes, the processing proceeds to I in  FIG. 142 . In the case of No, the processing returns to H in  FIG. 142 . 
       FIG. 144  illustrates the flow between the intercom outdoor unit  3001   c  and the deliverer mobile terminals  3001   f  after checking against the order number. The following is a description of  FIG. 144 . 
     In step  3007   a  subsequent to K in  FIG. 142 , the intercom outdoor unit  3001   c  checks whether a notification has been given regarding whether the blinks of the LED notified from the intercom indoor unit correspond to the order number. Here, in the case of No, the processing returns to K in  FIG. 142 . On the other hand, in the case of Yes, the processing proceeds to step  3007   b , where the intercom outdoor unit blinks the LED to show whether the blinks correspond to the order number, and the processing ends. 
     Furthermore, as illustrated in  FIG. 144 , in step  3007   c  subsequent to J in  FIG. 142 , the intercom indoor unit  3001   b  notifies the orderer by the display of the intercom indoor unit showing that the deliverer has arrived, with ring tone output. Next, in step  3007   d , the intercom indoor unit gives, to the intercom outdoor unit, an instruction to stop blinking the LED and an instruction to blink the LED to show that the blinks correspond to the order number. Then, the processing ends. 
     It should be noted that a delivery box for keeping a delivered product is often placed at the entrance, for instance, in the case where an orderer is not at home in an apartment, which is the delivery destination. A deliverer puts a delivery product in the delivery box if the orderer is not at home when the deliverer delivers the product. Using the LED of the deliverer mobile terminal  3001   f , optical communication is performed with the camera of the intercom outdoor unit  3001   c  to transmit the size of the delivery product, whereby the intercom outdoor unit  3001   c  automatically allows only a delivery box to be used which has a size corresponding to the delivery product. 
     As described above, according to Embodiment 8, cooperation between a device and web information can be achieved using optical communication. 
     Embodiment 9 
     The following is a description of Embodiment 9. 
     (Registration of User and Mobile Phone in Use to Server) 
       FIG. 145  is a diagram, for describing processing of registering a user and a mobile phone in use to a server according to the present embodiment. The following is a description of  FIG. 145 . 
     First, a user activates an application in step  4001   b.    
     Next, in step  4001   c , an inquiry as to information on this user and his/her mobile phone is made to a server. 
     Next, it is checked in step  4001   d  whether user information and information on a mobile phone in use are registered in a database (DB) of the server. 
     In the case of Yes, the processing proceeds to step  4001   f , where the analysis of a user voice characteristic (processing a) is started as parallel processing, and the processing proceeds to B in  FIG. 147 . 
     On the other hand, in the case of No, the processing proceeds to step  4001   e , where a mobile phone ID and a user ID are registered into a mobile phone table of the DB, and the processing proceeds to B in  FIG. 147 . 
     (Processing a: Analyzing User Voice Characteristics) 
       FIG. 146  is a diagram for describing processing of analyzing user voice characteristics according to the present embodiment. 
     The following is a description of  FIG. 146 . 
     First, in step  4002   a , sound is collected from a microphone. 
     Next, in step  4002   b , it is checked whether the collected sound is estimated to be the user voice, as a result of sound recognition. Here, in the case of No, the processing returns to step  4002   a.    
     In the case of Yes, the processing proceeds to step  4002   c , where it is checked whether what is said is a keyword (such as “next” and “return”) used for this application. In the case of Yes, the processing proceeds to step  4002   f , where voice data is registered into a user keyword voice table of the server, and the processing proceeds to step  4002   d . On the other hand, in the case of No, the processing proceeds to step  4002   d.    
     Next, in step  4002   d , voice characteristics (frequency, sound pressure, rate of speech) are analyzed. 
     Next, in step  4002   e , the analysis result is registered into the mobile phone and a user voice characteristic table of the server. 
     (Preparation for Sound Recognition Processing) 
       FIG. 147  is a diagram for describing processing of preparing sound recognition processing according to the present embodiment. The following is a description of  FIG. 147 . 
     First, in step  4003   a  subsequent to B in the diagram, operation for displaying a cooking menu list is performed (user operation). 
     Next, in step  4003   b , the cooking menu list is obtained from the server. 
     Next, in step  4003   c , the cooking menu list is displayed on a screen of the mobile phone. 
     Next, in step  4004   d , collecting sound is started using the microphone connected to the mobile phone. 
     Next, in step  4003   e , collecting sound by a sound collecting device in the vicinity thereof is started (processing b) as parallel processing. 
     Next, in step  4003   f , the analysis of environmental sound characteristics is started as parallel processing (processing c). 
     Next, in step  4003   g , cancellation of the sound output from a sound output device which is present in the vicinity is started (processing d) as parallel processing. 
     Next, in step  4003   h , user voice characteristics are obtained from the DB of the server. 
     Finally, in step  40031 , recognition of user voice is started, and the processing proceeds to C in  FIG. 151 . 
     (Processing b: Collecting Sound by Sound Collecting Device in Vicinity) 
       FIG. 148  is a diagram for describing processing of collecting sound by a sound collecting device in the vicinity according to the present embodiment. The following is a description of  FIG. 148 . 
     First, in step  4004   a , a device which can communicate with a mobile phone and collect sound (a sound collecting device) is searched for. 
     Next, in step  4004   b , it is checked whether a sound collecting device has been detected. 
     Here, in the case of No, the processing ends. In the case of Yes, the processing proceeds to step  4004   c , where position information and microphone characteristic information of the sound collecting device are obtained from the server. 
     Next, in step  4004   d , it is checked whether the server has such information. 
     In the case of Yes, the processing proceeds to step  4004   e , where it is checked whether the location of the sound collecting device is sufficiently close to the position of the mobile phone, so that the user voice can be collected. It should be noted that in the case of No in step  4004   e , the processing returns to step  4004   a . On the other hand, in the case of Yes in step  4004   e , the processing proceeds to step  4004   f , where the sound collecting device is caused to start collecting sound. Next, in step  4004   g , the sound collected by the sound collecting device is transmitted to the mobile phone until an instruction to terminate sound collecting processing is given. It should be noted that rather than transmitting the collected sound to the mobile phone as it is, the result obtained by sound recognition may be transmitted to the mobile phone. Further, the sound transmitted to the mobile phone is processed similarly to the sound collected from the microphone connected to the mobile phone, and the processing returns to step  4004   a.    
     It should be noted that in the case of No in step  4004   d , the processing proceeds to step  4004   h , where the sound collecting device is caused to start collecting sound. Next, in step  40041 , a tone is output from the mobile phone. Next, in step  4004   j , the voice collected by the sound collecting device is transmitted to the mobile phone. Next, in step  4004   k , it is checked whether a tone has been recognized based on the sound transmitted from the sound collecting device. Here, in the case of Yes, the processing proceeds to step  4004   g , whereas the processing returns to step  4004   a  in the case of No. 
     (Processing c: Analyzing Environmental Sound Characteristics) 
       FIG. 149  is a diagram for describing processing of analyzing environmental sound characteristics according to the present embodiment. The following is a description of  FIG. 149 . 
     First, in step  4005   f , the list of devices is obtained which excludes any device whose position is sufficiently far from the position of a microwave, among the devices which this user owns. Data of sounds output by these devices is obtained from the DB. 
     Next, in step  4005   g , the characteristics (frequency, sound pressure, and the like) of the obtained sound data are analyzed, and stored as environmental sound characteristics. It should be noted that particularly the sound output by, for instance, a rice cooker near the microwave tends to be incorrectly recognized, and thus characteristics thereof are stored with high importance being set 
     Next, sound is collected by a microphone in step  4005   a.    
     Next, it is checked in step  4005   b  whether the collected sound is user voice, and in the case of Yes, the processing returns to step  4005   a . In the case of No, the processing proceeds to step  4005   c , where characteristics (frequency, sound pressure) of the collected sound are analyzed. 
     Next, in step  4005   d , environmental sound characteristics are updated based on the analysis result. 
     Next, in step  4005   e , it is checked whether an ending flag is on, and the processing ends in the case of Yes, whereas the processing returns to step  4005   a  in the case of No. 
     (Processing d: Cancelling Sound from Sound Output Device Present in Vicinity) 
       FIG. 150  is a diagram for describing processing of canceling sound from a sound output device which is present in the vicinity according to the present embodiment. The following is a description of  FIG. 150 . 
     First, in step  4006   a , a device which can communicate and output sound (sound output device) is searched for. 
     Next, in step  4006   b , it is checked whether a sound output device has been detected, and the processing ends in the case of No. In the case of Yes, the processing proceeds to step  4006   c , where the sound output device is caused to output tones including various frequencies. 
     Next, in step  4006   d , the mobile phone and the sound collecting device in  FIG. 148  (sound collecting devices) collect the sound, thereby collecting the tones output from the sound output device. 
     Next, it is checked in step  4006   e  whether a tone has been collected and recognized. The processing ends in the case of No. In the case of Yes, the processing proceeds to step  4006   f , where transmission characteristics from the sound output device to each sound collecting device are analyzed (a relationship for each frequency between the output sound volume and the volume of collected sound and the delay time between the output of a tone and collection of the sound). 
     Next, it is checked in step  4006   g  whether sound data output from the sound output device is accessible from the mobile phone. 
     Here, in the case of Yes, the processing proceeds to step  4006   h , where until an instruction is given to terminate cancellation processing, an output sound source, an output portion, and the volume are obtained from the sound output device, and the sound output by the sound output device is canceled from the sound collected by the sound collecting devices in consideration of the transmission characteristics. The processing returns to step  4006   a . On the other hand, in the case of No, the processing proceeds to step  4006   i , where until an instruction is given to terminate cancellation processing, the output sound from the sound output device is obtained, and the sound output by the sound output device is canceled from the sound collected by the sound collecting devices in consideration of the transmission characteristics. The processing returns to step  4006   a.    
     (Selection of What to Cook, and Setting Detailed Operation in Microwave) 
       FIG. 151  is a diagram for describing processing of selecting what to cook and setting detailed operation of a microwave according to the present embodiment. The following is a description of  FIG. 151 . 
     First, in step  4007   a  subsequent to C in the diagram, what to cook is selected (user operation). 
     Next, in step  4007   b , recipe parameters (the quantity to cook, how strong the taste is to be, a baking degree, and the like) are set (user operation). 
     Next, in step  4007   c , recipe data and a detailed microwave operation setting command are obtained from the server in accordance with the recipe parameters. 
     Next, in step  4007   d , the user is prompted to bring the mobile phone to touch a noncontact integrated circuit (IC) tag embedded in the microwave. 
     Next, in step  4007   e , it is checked whether the microwave being touched is detected. 
     Here, in the case of No, the processing returns to step  4007   e . In the case of Yes, the processing proceeds to step  4007   f , where the microwave setting command obtained from the server is transmitted to the microwave. Accordingly, all the settings for the microwave necessary for this recipe are made, and the user can cook by only pressing an operation start button of the microwave. 
     Next, in step  4007   g , notification sound for the microwave is obtained from the DB of the server, for instance, and set in the microwave (processing e). 
     Next, in step  4007   h , the notification sound of the microwave is adjusted (processing f), and the processing proceeds to D in  FIG. 155 . 
     (Processing e: Obtaining Notification Sound for Microwave from DB of Server, for Instance, and Set in Microwave) 
       FIG. 152  is a diagram for describing processing of obtaining notification sound for a microwave from a DB of a server, for instance, and setting the sound in the microwave according to the present embodiment. The following is a description of  FIG. 152 . 
     First, in step  4008   a , the user brings the mobile phone close to (=to touch) the noncontact IC tag embedded in the microwave. 
     Next, in step  4008   b , an inquiry is made as to whether notification sound data for the mobile phone (data of sound output when the microwave is operating and ends operation) is registered in the microwave. 
     Next, it is checked in step  4008   c  whether the notification sound data for the mobile phone is registered in the microwave. 
     Here, in the case of Yes, the processing ends. In the case of No, the processing proceeds to step  4008   d , where it is checked whether the notification sound data for the mobile phone is registered in the mobile phone. In the case of Yes, the processing proceeds to step  4008   h , where the notification sound data registered in the mobile phone is registered in the microwave, and the processing ends. In the case of No, the processing proceeds to step  4008   e , where the DB of the server, the mobile phone, or the microwave is referred to. 
     Next, in step  4008   f , if notification sound data for the mobile phone (data of notification sound which this mobile phone can easily recognize) is in the DB, that data is obtained from the DB, whereas if such data is not in the DB, notification sound data for typical mobile phones (data of typical notification sound which mobile phones can easily recognize) is obtained from the DB. 
     Next, in step  4008   g , the obtained notification sound data is registered in the mobile phone. 
     Next, in step  4008   h , the notification sound data registered in the mobile phone is registered in the microwave, and the processing ends. 
     (Processing f: Adjusting Notification Sound of Microwave) 
       FIG. 153  is a diagram for describing processing of adjusting notification sound of a microwave according to the present embodiment. The following is a description of  FIG. 153 . 
     First, in step  4009   a , notification sound data of the microwave registered in the mobile phone is obtained. 
     Next, in step  4009   b , it is checked whether a frequency of the notification sound for the terminal and a frequency of environmental sound overlap a certain amount or more. 
     Here, in the case of No, the processing ends. 
     However, in the case of Yes, the processing proceeds to step  4009   c , where the volume of notification sound is set so as to be sufficiently larger than the environmental sound. Alternatively, the frequency of the notification sound is changed. 
     Here, as an example of a method for generating notification sound having a changed frequency, if the microwave can output the sound in (c) of  FIG. 154 , notification sound is generated in the pattern in (c), and the processing ends. If the microwave cannot output sound in (c), but can output the sound in (b), notification sound is generated in the pattern in (b), and the processing ends. If the microwave can output only the sound in (a), notification sound is generated in the pattern in (a), and the processing ends. 
       FIG. 154  is a diagram illustrating examples of waveforms of notification sounds set in a microwave according to the present embodiment. 
     The waveform illustrated in (a) of  FIG. 154  includes simple square waves, and almost all sound output devices can output sound in the waveform. Since the sound in the waveform is easily mixed up with sound other than notification sound, the sound is output several times, and if the sound can be recognized some of the several times, it is to be determined that the output of the notification sound is recognized, which is an example of handling such case. 
     The waveform illustrated in (b) of  FIG. 154  is a waveform obtained by sectioning the waveform in (a) finely at short square waves, and such sound in the waveform can be output if the operation clock frequency of a sound output device is high enough. Although people hear this sound as similar sound to the sound in (a), a feature of the sound is that the sound has a greater amount of information than (a), and tends not to be mixed up with sound other than notification sound in machine recognition. 
     The waveform illustrated in (c) of  FIG. 154  is obtained by changing the temporal lengths of sound output portions, and is referred to as a pulse-width modulation (PWM) waveform. Although it is more difficult to output such sound in the PWM waveform than the sound in (b), the sound in the PWM waveform has a greater amount of information than the sound in (b), thus improving a recognition rate and also allowing information to be transmitted from the microwave to the mobile phone simultaneously. 
     It should be noted that although the sounds in the waveforms in (b) and (c) of  FIG. 154  are less likely to be incorrectly recognized than the sound illustrated in (a) of  FIG. 154 , the recognition rate of the sounds can be further improved by repeating the sounds in the same waveform several times, as with the sound in (a) of  FIG. 154 . 
     (Display of Details of Cooking) 
       FIG. 155  is a diagram illustrating examples of waveforms of notification sounds set in a microwave according to the present embodiment. The following is a description of  FIG. 155 . 
     First, the details of cooking are displayed in step  4011   a  subsequent to D in the diagram. 
     Next, it is checked in step  4011   b  whether the cooking in detail is to be done by the operation of the microwave. 
     Here, in the case of Yes, the processing proceeds to step  4011   c , where the user is notified that food is to be put in the microwave, and the operation start button is to be pressed. The processing proceeds to E in  FIG. 156 . 
     On the other hand, in the case of No, the processing proceeds to step  4011   d , where the details of cooking are displayed, and the processing proceeds to F in the diagram or proceeds to step  4011   e.    
     In step  4011   e , it is checked whether the operation is performed by the user. If the application has ended, the processing ends. 
     On the other hand, in the case of operation of changing display content, manual input (pressing a button, for instance), or voice input (such as “next”, “previous”), the processing proceeds to step  4011   f , where it is checked whether cooking ends as a result of changing the display content. Here, in the case of Yes, the processing proceeds to step  4011   g , where the user is notified of the end of cooking, and the processing ends. In the case of No, the processing proceeds to step  4011   a.    
     (Recognition of Notification Sound of Microwave) 
       FIG. 156  is a diagram for describing processing of recognizing notification sound of a microwave according to the present embodiment. The following is a description of  FIG. 156 . 
     First, in step  4012   a  subsequent to E in the diagram, collecting sound by a sound collecting device in the vicinity and recognition of notification sound of the microwave are started (processing g) as parallel processing. 
     Next, in step  4012   f , checking of the operation state of the mobile phone is started (processing i) as parallel processing. 
     Next, in step  4012   g , tracking a user position is started (processing j) as parallel processing. 
     Next, the details of recognition are checked in step  4012   b.    
     Here, if notification sound indicating a button being pressed has been recognized, the processing proceeds to step  4012   c , where the change of the setting is registered, and the processing returns to step  4012   b . If operation by the user is recognized, the processing proceeds to F in  FIG. 155 . If notification sound indicating the end of operation or the sound of opening the door of the microwave is recognized after an operation time elapses since the display is presented to prompt the user to put food into the microwave and press the operation start button, the user is notified of the end of operation of the microwave (processing h) in step  4012   e , and the processing proceeds to G in  FIG. 155 . If the notification sound indicating the start of the operation is recognized, the processing proceeds to step  4012   d , where the elapse of the operation time is waited for, and the processing proceeds to step  4012   e , where the user is notified of the end of operation of the microwave (processing h). Then, the processing proceeds to G in  FIG. 155 . 
     (Processing g: Collecting Sound by Sound Collecting Device in Vicinity and Recognizing Notification Sound of Microwave) 
       FIG. 157  is a diagram for describing processing of collecting sound by a sound collecting device in the vicinity and recognizing notification sound of a microwave according to the present embodiment. The following is a description of  FIG. 157 . 
     First, in step  4013   a , a device (sound collecting device) is searched for which can communicate with a mobile phone and collect sound. 
     Next, it is checked in step  4013   b  whether a sound collecting device has been detected. 
     Here, in the case of No, the processing ends. On the other hand, in the case of Yes, the processing proceeds to step  4013   c , where the position information of the sound collecting device and microphone characteristics information are obtained from the server. 
     Next, in step  4013   d , it is checked whether the server has that information. 
     In the case of Yes, the processing proceeds to step  4013   r , where it is checked whether the location of the sound collecting device is close enough to the microwave so that notification sound can be collected. 
     Here, in the case of No in step  4013   r , the processing returns to step  4013   a . In the case of Yes, the processing proceeds to step  4013   s , where it is checked whether an arithmetic unit of the sound collecting device can perform sound recognition. In the case of Yes in step  4013   s , information for recognizing notification sound of the microwave is transmitted to the sound collecting device in step  4013   u . Next, in step  4013   v , the sound collecting device is caused to start collecting and recognizing sound, and transmit the recognition results to the mobile phone. Next, in step  4013   q , processing of recognizing notification sound of the microwave is performed until the cooking procedure proceeds to the next cooking step, and the recognition results are transmitted to the mobile phone. On the other hand, in the case of No in step  4013   s , the processing proceeds to step  4013   t , where the sound collecting device is caused to start collecting sound, and transmit collected sound to the mobile phone. Next, in step  4013   j , the sound collecting device is caused to transmit the collected sound to the mobile phone until the cooking procedure proceeds to the next cooking step, and the mobile phone identifies notification sound of the microwave. 
     It should be noted that in the case of No in step  4013   d , the processing proceeds to step  4013   e , where it is checked whether the arithmetic unit of the sound collecting device can perform sound recognition. 
     In the case of Yes, the processing proceeds to step  4013   k , where information for recognizing notification sound of the microwave is transmitted to the sound collecting device. Next, in step  4013   m , the sound collecting device is caused to start collecting sound and recognizing sound, and transmit the recognition results to the mobile phone. Next, in step  4013   n , notification sound of the microwave is output. Next, in step  4013   p , it is checked whether the sound collecting device has successfully recognized the notification sound. In the case of Yes in step  4013   p , the processing proceeds to  4013   q , where the sound collecting device is caused to perform processing of recognizing the notification sound of the microwave until the cooking procedure proceeds to the next cooking step, and transmit the recognition results to the mobile phone, and then the processing returns to step  4013   a . In the case of No in step  4013   p , the processing returns to step  4013   a.    
     Further, in the case of No in step  4013   e , the processing proceeds to step  4013   f , where the sound collecting device is caused to start collecting sound, and transmit the collected sound to the mobile phone. Next, in step  4013   g , the notification sound of the microwave is output. Next, in step  4013   h , recognition processing is performed on the sound transmitted from the sound collecting device. Next, in step  4013   i , it is checked whether the notification sound has been successfully recognized. Here, in the case of Yes, the processing proceeds to  4013   j , where the sound collecting device is caused to transmit the collected sound to the mobile phone until the cooking procedure proceeds to the next cooking step, and the mobile phone recognizes the notification sound of the microwave, and then the processing returns to step  4013   a . In the case of No, the processing returns to step  4013   a.    
     (Processing h: Notifying User of End of Operation of Microwave) 
       FIG. 158  is a diagram for describing processing of notifying a user of the end of operation of the microwave according to the present embodiment. The following is a description of  FIG. 158 . 
     First, in step  4013   a , it is checked whether it can be determined that the mobile phone is currently being used or carried using sensor data. It should be noted that in the case of Yes, the processing proceeds to step  4014   m , where the user is notified of the end of operation of the microwave using screen display, sound, and vibration of the mobile phone, for instance, and the processing ends. 
     On the other hand, in the case of No in step  4013   a , the processing proceeds to step  4014   b , where a device which is being operated (a device under user operation) is searched for from among devices such as a personal computer (PC) which the user has logged in. 
     Next, it is checked in step  4014   c  whether the device under user operation has been detected. It should be noted that in the case of Yes, the user is notified of the end of operation of the microwave using, for instance, the screen display of the device under user operation, and the processing ends. 
     In the case of No in step  4014   c , the processing proceeds to step  4014   e , where a device (imaging device) is searched for which can communicate with the mobile phone and obtain images. 
     Next, it is checked in step  4014   f  whether an imaging device has been detected. 
     Here, in the case of Yes, the processing proceeds to step  4014   p , where the imaging device is caused to capture an image, transmit data of a user face to the imaging device itself, and then recognize the user face. Alternatively, the imaging device is caused to transmit the captured image to the mobile phone or the server, and the user face is recognized at the destination to which the image is transmitted. 
     Next, it is checked in step  4014   q  whether the user face has been recognized. In the case of No, the processing returns to step  4014   e . In the case of Yes, the processing proceeds to step  4014   r , where it is checked whether a device (detection device) which has detected the user includes a display unit and a sound output unit. In the case of Yes in step  4014   r , the processing proceeds to step  4014   s , where the user is notified of the end of operation of the microwave using the unit included in the device, and the processing ends. 
     In the case of No in step  4014   f , the processing proceeds to step  4014   g , where a device (sound collecting device) is searched for which can communicate with the mobile phone and collect sound. 
     In the case of No in step  4014   h , the processing proceeds to step  4014   i , where another device is detected which can determine a position of the user by operation of the device, by means of walk vibration, and the like. Next, the processing proceeds to step  4014   m , where the user is notified of the end of operation of the microwave using, for instance, screen display, sound, and vibration of the mobile phone, and the processing ends. 
     It should be noted that in the case of Yes in step  40141 , the processing proceeds to step  4014   r , where it is checked whether a device (detection device) which has detected the user includes a display unit and a sound output unit. Here, in the case of No, the position information of a detection device is obtained from the server. 
     Next, in step  4014   u , a device (notification device) which is near the detection device, and includes a display unit and a sound output unit is searched for. Next, in step  4014   v , the user is notified of the end of operation of the microwave by a screen display or sound of sufficient volume in consideration of the distance from the notification device to the user, and the processing ends. 
     (Processing i: Checking Operation State of Mobile Phone) 
       FIG. 159  is a diagram for describing processing of checking an operation state of a mobile phone according to the present embodiment. The following is a description of  FIG. 159 . 
     First, it is checked in step  4015   a  whether the mobile phone is being operated, the mobile phone is being carried, an input/output device connected to the mobile phone has received input and output, video and music are being played back, a device located near the mobile phone is being operated, or the user is recognized by a camera or various sensors of a device located near the mobile phone. 
     Here, in the case of Yes, the processing proceeds to step  4015   b , where it is acknowledged that there is a high probability that the position of the user is close to this mobile phone. Then, the processing returns to step  4015   a.    
     On the other hand, in the case of No, the processing proceeds to step  4015   c , where it is checked whether a device located far from the mobile phone is being operated, the user is recognized by a camera or various sensors of the device located far from the mobile phone, or the mobile phone is being charged. 
     In the case of Yes in step  4015   c , the processing proceeds to step  4015   d , where it is acknowledged that there is a high probability that the position of the user is far from this mobile phone, and the processing returns to step  4015   a . In the case of No in step  4015   c , the processing returns to step  4015   a.    
     (Processing j: Tracking User Position) 
       FIG. 160  is a diagram for describing processing of tracking a user position according to the present embodiment. The following is a description of  FIG. 160 . 
     First, in step  4016   a , it is checked whether or not the mobile phone is determined as being carried, using a bearing sensor, a position sensor, or a 9-axis sensor. The 9-axis sensor is a sensor including at least one of an accelerometer, an angular velocity sensor, and a geomagnetic sensor. 
     In the case of Yes in step  4016   a , the processing proceeds to step  4016   b , where the positions of the mobile phone and the user are registered into the DB, and the processing returns to step  4016   a.    
     On the other hand, in the case of No in step  4016   a , the processing proceeds to step  4016   c , where a device (user detection device) is searched for which can communicate with the mobile phone, and detect a user position and the presence of the user, such as a camera, a microphone, or a human sensing sensor. 
     Next, it is checked in step  4016   d  whether a sound collecting device is detected. In the case of No in step  4016   d , the processing returns to step  4016   a.    
     In the case of Yes in step  4016   d , the processing proceeds to step  4016   e , where it is checked whether the user detection device detects the user. In the case of No in step  4016   e , the processing returns to step  4016   a.    
     In the case of Yes in step  4016   e , the processing proceeds to step  4016   f , where the detection of the user is transmitted to the mobile phone. 
     Next, in step  4016   g , the user being present near the user detection device is registered into the DB. 
     Next, in step  4016   h , if the DB has position information of the user detection device, the information is obtained, thereby determining the position of the user, and the processing returns to step  4016   a.    
       FIG. 161  is a diagram illustrating that while canceling sound from a sound output device, notification sound of a home electric appliance is recognized, an electronic device which can communicate is caused to recognize a current position of a user (operator), and based on the recognition result of the user position, a device located near the user position is caused to give a notification to the user. Further,  FIG. 162  is a diagram illustrating content of a database held in a server, a mobile phone, or a microwave according to the present embodiment. 
     As illustrated in  FIG. 162 , on a microwave table  4040   a , the model of a microwave, data for identifying sound which can be output (speaker characteristics, a modulation method, and the like), for each of various mobile phone models, data of notification sound having characteristics easily recognized by the mobile phone, and data of notification sound easily recognized by a typical mobile phone on the average are held in association with one another. 
     A mobile phone table  4040   b  holds mobile phones, and for each of the mobile phones, the model of the mobile phone, a user who uses the mobile phone, and data indicating the position of the mobile phone in association with one another. 
     A mobile phone model table  4040   c  holds the model of a mobile phone, sound-collecting characteristics of a microphone which is an accessory of the mobile phone of the model in association with each other. 
     A user voice characteristic table  4040   d  holds a user and an acoustic feature of the user voice in association with each other. 
     A user keyword voice table  4040   e  holds a user and voice waveform data obtained when the user says keywords such as “next” and “return” to be recognized by a mobile phone in association with each other. It should be noted that this data may be obtained by analyzing and changing in the form with which the data is easily handled, rather than the voice waveform data as is. 
     A user owned device position table  4040   f  holds a user, a device that the user owns, and position data of the device in association with one another. 
     A user owned device position table  4040   g  holds a user, a device that the user owns, and data of sound such as notification sound and operation sound output by the device in association with one another. 
     A user position table  4040   h  holds a user and data of a position of the user in association with each other. 
       FIG. 163  is a diagram illustrating that a user cooks based on cooking processes displayed on a mobile phone, and further operates the display content of the mobile phone by saying “next”, “return”, and others according to the present embodiment.  FIG. 164  is a diagram illustrating that the user has moved to another place while he/she is waiting until the operation of a microwave ends after starting the operation or while he/she is stewing food according to the present embodiment.  FIG. 165  is a diagram illustrating that a mobile phone transmits an instruction to detect the user to a device which is connected to the mobile phone via a network, and can recognize a position of the user and the presence of the user, such as a camera, a microphone, or a human sensing sensor.  FIG. 166  illustrates that as an example of user detection, a user face is recognized using a camera included in a television, and further the movement and presence of the user are recognized using a human sensing sensor of an air-conditioner. It should be noted that a television and an air-conditioner may perform this recognition processing, or image data or the like may be transmitted to a mobile phone or a server, and recognition processing may be performed at the transmission destination. From a viewpoint of privacy protection, it is better not to transmit data of the user to an external server. 
       FIG. 167  illustrates that devices which have detected the user transmit to the mobile phone the detection of the user and a relative position of the user to the devices which have detected the user. 
     As described above, it is possible to determine a user position if the DB has position information of a device which has detected the user. 
       FIG. 168  is a diagram illustrating that the mobile phone recognizes microwave operation end sound according to the present embodiment.  FIG. 169  illustrates that the mobile phone which has recognized the end of the operation of the microwave transmits an instruction to, among the devices which have detected the user, a device having a screen-display function or a sound output function (the television in front of the user in this drawing) to notify the user of the end of the microwave operation. 
       FIG. 170  illustrates that the device which has received the instruction notifies the user of the details of the notification (in the drawing, the television displays the end of operation of the microwave on the screen thereof).  FIG. 171  is a diagram illustrating that a device which is present near the microwave is connected to the mobile phone via a network, and includes a microphone recognizes the microwave operation end sound.  FIG. 172  is a diagram illustrating that the device which has recognized the end of operation of the microwave notifies the mobile phone thereof.  FIG. 173  illustrates that if the mobile phone is near the user when the mobile phone receives the notification indicating the end of the operation of the microwave, the user is notified of the end of the operation of the microwave, using screen display, sound output, and the like by the mobile phone. 
       FIG. 174  is a diagram illustrating that the user is notified of the end of the operation of the microwave. Specifically,  FIG. 174  illustrates that if the mobile phone is not near the user when the mobile phone receives the notification indicating the end of the operation of the microwave, an instruction is transmitted to, among the devices which have detected the user, a device having a screen display function or a sound output function (the television in front of the user in this drawing) to notify the user of the end of the operation of the microwave, and the device which has received the instruction notifies the user of the end of the operation of the microwave. This drawing illustrates that there are often cases where the mobile phone is not present near the microwave nor the user when the mobile phone is connected to a charger, and thus the illustrated situation tends to occur. 
       FIG. 175  is a diagram illustrating that the user who has received the notification indicating the end of the operation of the microwave moves to a kitchen. It should be noted that the mobile phone shows what to do next for the cooking at this time. Further, the mobile phone may recognize that the user has moved to the kitchen by sound, for instance, and start giving explanation of the next process of the cooking in a timely manner. 
       FIG. 176  illustrates that the microwave transmits information such as the end of operation to the mobile phone by wireless communication, the mobile phone gives a notification instruction to the television which the user is watching, and the user is notified by a screen display or sound of the television. 
     It should be noted that a home LAN, direct wireless communication, especially the wireless communication of 700 MHz to 900 MHz, for instance, can be utilized for communication between an information source device (the microwave in this drawing) and the mobile phone and communication between the mobile phone and a device which gives a notification to the user (the television in this drawing). Further, although the mobile phone is utilized as a hub here, another device having communication capability may be utilized instead of the mobile phone. 
       FIG. 177  illustrates that the microwave transmits information such as the end of operation to the television which the user is watching by wireless communication, and the user is notified thereof using the screen display or sound of the television. This illustrates the operation performed when communication is performed not via the mobile phone serving as a hub in  FIG. 176 . 
       FIG. 178  illustrates that if an air-conditioner on the first floor notifies the user of certain information, the air-conditioner on the first floor transmits information to an air-conditioner on the second floor, the air-conditioner on the second floor transmits the information to the mobile phone, the mobile phone gives a notification instruction to the television which the user is watching, and the user is notified thereof by the screen display or sound of the television. This shows that an information source device (the air-conditioner on the first floor in this drawing) cannot directly communicate with the mobile phone serving as a hub, the information source device transmits information to another device which can communicate therewith, and establishes communication with the mobile phone. 
       FIG. 179  is a diagram illustrating that a user who is at a remote place is notified of information. Specifically,  FIG. 179  illustrates that the mobile phone which has received a notification from the microwave by sound, optically, or via wireless communication, for instance, notifies the user at a remote place of information via the Internet or carrier communication.  FIG. 180  illustrates that if the microwave cannot directly communicate with the mobile phone serving as a hub, the microwave transmits information to the mobile phone via a personal computer, for instance.  FIG. 181  illustrates that the mobile phone which has received communication in  FIG. 180  transmits information such as an operation instruction to the microwave, following the information-and-communication path in an opposite direction. 
     It should be noted that the mobile phone may automatically transmit information in response to the information in  FIG. 180 , notify the user of the information, and transmit information on the operation performed by the user in response to the notification. 
       FIG. 182  illustrates that in the case where the air-conditioner which is an information source device cannot directly communicate with the mobile phone serving as a hub, the air-conditioner notifies the user of information. Specifically,  FIG. 182  illustrates that in the case where the air-conditioner which is an information source device cannot directly communicate with the mobile phone serving as a hub, first, information is transmitted to a device such as a personal computer which establishes one step of communication with the mobile phone as shown by A, the information is transmitted to the mobile phone from the personal computer via the Internet or a carrier communication network as shown by B and C, and the mobile phone processes the information automatically, or the user operates the mobile phone, thereby transmitting the information to the personal computer via the Internet or the carrier communication network as shown by D and E, the personal computer transmits a notification instruction to a device (the television in this drawing) which can notify the user who the computer wants to notify the information as shown by F, and the user is notified of the information using the screen display or sound of the television as shown by G. 
     Such a situation tends to occur if the user to receive notification information from the air-conditioner is different from the user who is using the mobile phone. 
     It should be noted that although communication between the personal computer and the mobile phone is established via the Internet or the carrier communication network in this drawing, communication may be established via a home LAN, direct communication, or the like. 
       FIG. 183  is a diagram for describing a system utilizing a communication device which uses a 700 to 900 MHz radio wave. Specifically, with the configuration in  FIG. 183 , a system is described which utilizes a communication unit (referred to as a G unit in the following) which uses a 700 to 900 MHz radio wave (referred to as a G radio wave in the following).  FIG. 183  illustrates that the microwave having a G unit transmits information, using a G radio wave, to a mobile phone on the third floor having a G unit, the mobile phone on the third floor having the G unit transmits, utilizing a home network, the information to a mobile phone on the second floor which does not have a G unit, and the user is notified of the information from the mobile phone on the second floor. 
     It should be noted that for registration and authentication of communication between devices each having a G unit, a method using the NFC function of both the devices can be considered. In addition, if one of the devices does not have the NFC function, the output of a G radio wave is lowered so that communication is possible only in a range of about 10 to 20 cm, and both the devices are brought close to each other. If communication is successfully established, communication between the G units is registered and authenticated, which is a conceivable method as a registration mode. 
     In addition, an information source device (the microwave in this drawing) may be a device other than a microwave, as long as the device has a G unit. 
     In addition, a device (the mobile phone on the third floor in this drawing) which relays communication between the information source device and the information notification device (the mobile phone on the second floor in this drawing) may be a device such as a personal computer, an air-conditioner, or a smart meter rather than a mobile phone, as long as the device can access a G radio wave and a home network. 
     In addition, an information notification device may be a device such as a personal computer or a television rather than a mobile phone, as long as the device can access a home network, and give a notification to a user by using screen display, audio output, or the like. 
       FIG. 184  is a diagram illustrating that a mobile phone at a remote place notifies a user of information. Specifically,  FIG. 184  illustrates that an air-conditioner having a G unit transmits information to a mobile phone having a G unit in a house, the mobile phone in the house transmits the information to the mobile phone at the remote place via the Internet or a carrier communication network, and the mobile phone at the remote place notifies the user of the information. 
     It should be noted that the information source device (the air-conditioner in this drawing) may be a device other than a microwave, as long as the device has a G unit. 
     In addition, a device (the mobile phone in the house in this drawing) which relays communication between the information source device and the information notification device (the mobile phone at a remote place in this drawing) may be a device such as a personal computer, an air-conditioner, or a smart meter rather than a mobile phone, as long as the device can access a G radio wave, the Internet, or a carrier communication network. 
     It should be noted that the information notification device may be a device such as a personal computer or a television rather than a mobile phone, as long as the device can access the Internet or a carrier communication network, and give a notification to a user by using screen display, audio output, or the like. 
       FIG. 185  is a diagram illustrating that the mobile phone at a remote place notifies the user of information. Specifically,  FIG. 185  illustrates that a television having a G unit recognizes notification sound of the microwave which does not have a G unit and transmits information to the mobile phone having a G unit in the house via a G radio wave, the mobile phone in the house transmits the information to the mobile phone at a remote place via the Internet or a carrier communication network, and the mobile phone at the remote place notifies the user of the information. 
     It should be noted that another device may perform a similar operation to that of an information source device (the microwave in this drawing), and a method for a notification recognition device (the television in this drawing) to recognize notification from the information source device may be performed using, for instance, a light emission state rather than sound, which also achieves similar effects. 
     In addition, another device having a G unit may perform a similar operation to that of the notification recognition device. Further, a device (the mobile phone in the house in this drawing) which relays communication between the notification recognition device and the information notification device (the mobile phone at a remote place in this drawing) may be a device such as a personal computer, an air-conditioner, or a smart meter rather than a mobile phone, as long as the device can access a G radio wave, the Internet, or a carrier communication network. 
     It should be noted that the information notification device may be a device such as a personal computer or a television rather than a mobile phone, as long as the device can access the Internet or a carrier communication network and give a notification to a user using screen display and audio output, for instance. 
     In addition,  FIG. 186  is a diagram illustrating that in a similar case to that of  FIG. 185 , a television on the second floor serves as a relay device instead of a device (a mobile phone in the house in  FIG. 185 ) which relays communication between a notification recognition device (the television on the second floor in this drawing) and an information notification device (the mobile phone at a remote place in this drawing). 
     As described above, the device according to the present embodiment achieves the following functions.
         a function of learning user voice characteristics through the use of an application   a function of detecting a sound collecting device which can collect sound output from a mobile phone, from among devices which can communicate with the mobile phone and have a sound-collecting function   a function of detecting a sound collecting device which can collect sound output from an electronic device, from among devices which can communicate with a mobile phone and have a sound-collecting function   a function of causing a sound collecting device to transmit to a mobile phone as-is sound collected by the sound collecting device or a sound recognition result   a function of analyzing characteristics of environmental sound and improving accuracy of sound recognition   a function of obtaining, from a DB, sound which may be output from a device that a user owns and improving accuracy of sound recognition   a function of detecting a sound output device sound output from which can be collected by a mobile phone or a sound collecting device, from among devices which can communicate with the mobile phone and have a sound output function   a function of cancelling unnecessary sound from collected sound by obtaining audio data output from a sound output device, and subtracting the data from collected sound in consideration of transmission characteristics   a function of obtaining processes of cooking for giving instructions to a user, in response to the reception of input of parameters of a cooking recipe, and obtaining control data for controlling a cooking device from a server   a function of making settings so that a mobile phone and a sound collecting device easily recognize notification sound output from a device, based on data of sound which can be output by the device   a function of improving accuracy of recognizing user voice by adjusting a recognition function, based on user voice characteristics   a function of recognizing user voice using plural sound collecting devices   a function of recognizing notification sound of an electronic device using plural sound collecting devices   a function of obtaining necessary information from an electronic device and making settings in a microwave via, for instance, a mobile phone and a noncontact IC card of an electronic device in order to perform a series of operations only by one operation   a function of searching for a user using a device such as a camera, a microphone, or a human sensing sensor which can communicate with a mobile phone, and causing the device to transmit a current position of the user to the mobile phone or store the position into a DB   a function of notifying a user from a device located near the user using a position of the user stored in a DB   a function of estimating whether a user is present near a mobile phone, based on states (an operating condition, a sensor value, a charging state, a data link state, and the like) of the mobile phone       

     It should be noted that in the processing in  FIGS. 145 to 175 , similar functionality can be achieved even by changing sound data to light emission data (frequency, brightness, and the like), sound output to light emission, and sound collection to light reception, respectively. 
     In addition, although a microwave is used as an example in the present embodiment, an electronic device which outputs notification sound to be recognized may not be a microwave, but changed to a washing machine, a rice cooker, a cleaner, a refrigerator, an air cleaner, an electric water boiler, an automatic dishwasher, an air-conditioner, a personal computer, a mobile phone, a television, a car, a telephone, a mail receiving device, or the like, which also achieves similar effects. 
     In addition, although a microwave, a mobile phone, and a device such as a television which gives notification to a user establish direct communication to one another in the present embodiment, the devices may communicate with one another indirectly via another device if there is a problem with direct communication. 
     In addition, although communication established mainly utilizing a home LAN is assumed in the present embodiment, even direct wireless communication between devices and communication via the Internet or a carrier communication network can achieve similar functionality. 
     The present embodiment achieves effects of preventing leakage of personal information since a mobile phone makes simultaneous inquiry about the position of a user, to cause a camera of a TV, for instance, to perform person identification, and a coded result is transmitted to the mobile phone of that user. Even if there are two or more people in a house, data obtained by a human sensing sensor of an air-conditioner, an air cleaner, and a refrigerator is transmitted to a position control database of a mobile phone or the like, whereby the movement of an operator recognized once is tracked by the sensor. This allows the position of the operator to be estimated. 
     It should be noted that if a user owns a mobile phone having a gyroscope or an azimuth meter, data of identified position may be registered into a user position database. 
     In addition, when an operator places a mobile phone, the operation of a physical sensor firstly stops for a certain period of time, and thus this can be detected. Next, button operation and human sensing sensors of a home electric appliance and a light, a camera of a TV or the like, a microphone of the mobile phone, and the like are used to detect that the operator has left there. Then, the position of the operator is registered into a mobile phone or the user position database of a server in the house. 
     As described above, according to Embodiment 9, an information communication device (recognition device) which enables communication between devices can be achieved. 
     Specifically, the information communication device according to the present embodiment may include a recognition device which searches for an electronic device (sound collecting device) having sound-collecting functionality from among electronic devices which can communicate with an operation terminal, and recognizes, utilizing the sound-collecting functionality of the sound collecting device, notification sound of another electronic device. 
     Here, this recognition device may be a recognition device utilizing the sound-collecting functionality of only a sound collecting device which can collect tones output from the operation terminal. 
     In addition, the information communication device according to the present embodiment may include a sound collecting device which searches for an electronic device (sound output device) having sound output functionality from among electronic devices which can communicate with the operation terminal, analyzes sound transmission characteristics between the sound output device and the sound collecting device, obtains output sound data from the sound output device, and cancels, from the collected sound, sound output from the sound output device, based on the sound transmission characteristics and the output sound data. 
     In addition, the information communication device according to the present embodiment may include a recognition device which adjusts notification sound of electronic device whose notification sound is to be recognized so that the sound is prevented from being lost in environmental sound. 
     In addition, the information communication device according to the present embodiment may include a recognition device which stores, in a database, an electronic device owned by a user (owned electronic device), data of sound output by the owned electronic device, and position data of the owned electronic device, and adjusts notification sound of the electronic device to be recognized so that the sound output by the owned electronic device and the notification sound of the electronic device to be recognized are easily distinguished. 
     Here, this recognition device may further adjust sound recognition processing so that it is easy to distinguish between the sound output by an owned electronic device and the notification sound of the electronic device to be recognized. 
     In addition, the information communication device according to the present embodiment may include a recognition device which recognizes whether the positions of the operation terminal and an operator are close to each other, utilizing an operating condition of an operation terminal, a sensor value of a physical sensor, a data link state, and a charging state. 
     Here, this recognition device may further recognize a position of the user, utilizing an operating state of an electronic device which can communicate with an operation terminal, a camera, a microphone, a human sensing sensor, and position data of the electronic device stored in the database. 
     In addition, this recognition device may further be included in an information notifying device which notifies a user of information using the notification device which can give notification to the user, utilizing a recognition result of the user position, and position data, stored in the database, of an electronic device (notification device) which has a function of giving notification to the user by means of screen display, voice output, and the like. 
     It should be noted that these general and specific embodiments may be implemented using a system, a method, an integrated circuit, a computer program, or a recording medium, or any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     Embodiment 10 
     Currently, various simple authentication methods have been considered in wireless communication. For example, a push button method, a personal identification number (PIN) input method, an NFC method, and the like are specified in the Wi-Fi protected setup (WPS) of wireless LAN, which is set by the Wi-Fi alliance. With various simple authentication methods in wireless communication, whether a user using a device is to be authenticated is determined by limiting a time period or determining that the user is in a range where he/she can touch both devices, thereby authenticating the user. 
     However, it cannot be said that the method of limiting a time period is secured if a user with evil intention is at some short distance. In addition, there are cases where the user has difficulty or troublesome in directly touching an installed device such as a home electric appliance. 
     In view of this, in the present embodiment, a method of determining that a user who is to be authenticated is certainly in a room, and performing wireless authentication of a home electric appliance with ease and in a secured manner, by using communication using visible light for wireless authentication. 
       FIG. 187  is a diagram illustrating an example of an environment in a house in the present embodiment.  FIG. 188  is a diagram illustrating an example of communication between a smartphone and home electric appliances according to the present embodiment.  FIG. 189  is a diagram illustrating a configuration of a transmitter device according to the present embodiment.  FIG. 190  is a diagram illustrating a configuration of a receiver device according to the present embodiment.  FIGS. 187 to 190  are similar to  FIGS. 124 to 127 , and thus a detailed description thereof is omitted. 
     Home environment is assumed to be an environment where a tablet terminal which the user has in the kitchen and a TV placed in a living room are authenticated as illustrated in  FIG. 187 . Assume that both the devices are terminals which can be connected to a wireless LAN, and each include a WPS module. 
       FIG. 191  is a sequence diagram for when a transmitter terminal (TV) performs wireless LAN authentication with a receiver terminal (tablet terminal), using optical communication in  FIG. 187 . The following is a description of  FIG. 191 . 
     First, for example, a transmitter terminal as illustrated in  FIG. 189  creates a random number (step  5001   a ). Next, the random number is registered in a registrar of WPS (step  5001   b ). Furthermore, a light emitting element is caused to emit light as indicated by a pattern of the random number registered in the registrar (step  5001   c ). 
     On the other hand, while the light emitting element of the transmitter device is emitting light, a receiver device as illustrated in, for example,  FIG. 190  activates a camera thereof in an optical authentication mode. Here, the optical authentication mode is a mode in which it can be recognized that the light emitting element is emitting light for authentication, and is a video shooting mode which allows shooting in accordance with a cycle of light emissions. 
     Accordingly, a user shoots a light emitting element of the transmitter terminal, first (step  5001   d ). Next, the receiver terminal receives the random number by shooting (step  5001   e ). Next, the receiver terminal which has received the random number inputs the random number as a PIN of WPS (step  5001   f ). 
     Here, the transmitter and receiver terminals which share the PIN perform authentication processing according to the standard by WPS (step  5001   g ). 
     Next, when the authentication is completed, the transmitter terminal deletes the random number from the registrar, and avoids accepting authentication from a plurality of terminals ( 5001   h ). 
     It should be noted that this method is applicable not only to wireless LAN authentication, but also to all the wireless authentication methods which use a common key. 
     In addition, this method is not limited to a wireless authentication method. For example it is also applicable for authentication of an application loaded on both the TV and the tablet terminal. 
       FIG. 192  is a sequence diagram for when authentication is performed using an application according to the present embodiment. The following is a description of  FIG. 192 . 
     First, a transmitter terminal creates a transmitter ID according to the state of the terminal (step  5002   a ). Here, the transmitter ID may be a random number or a key for coding. In addition, a terminal ID (a MAC address, an IP address) of the transmitter terminal may be included. Next, the transmitter terminal emits light as indicated by the pattern of the transmitter ID (step  5002   b ). 
     On the other hand, a receiver device receives the transmitter ID in the same process as in the case of wireless authentication (step  5002   f ). Next, upon the reception of the transmitter ID, the receiver device creates a receiver ID which can show that the transmitter ID has been received (step  5002   g ). For example, the receiver ID may be a terminal ID of the receiver terminal coded in the transmitter ID. In addition, the receiver ID may also include a process ID and a password of an application which has been activated in the receiver terminal. Next, the receiver terminal broadcasts the receiver ID wirelessly (step  5002   h ). It should be noted that if a terminal ID of the transmitter terminal is included in the transmitter ID, the receiver terminal may unicast the receiver ID 
     Next, the transmitter terminal which has received the receiver ID wirelessly ( 5002   c ) performs authentication with a terminal which has transmitted the received receiver ID, using the transmitter ID shared in both the terminals (step  5002   d ). 
       FIG. 193  is a flowchart illustrating operation of the transmitter terminal according to the present embodiment. The following is a description of  FIG. 193 . 
     First, the transmitter terminal emits light indicating an ID, according to the state of the terminal (step  5003   a ). 
     Next, light is emitted by the pattern according to the ID (step  5003   b ). 
     Next, it is checked whether there is a wireless response corresponding to the ID indicated by emitted light (step  5003   c ). If there is a response (Yes in step  5003   c ), processing of authenticating the terminal which has transmitted the response is performed (step  5003   d ). It should be noted that if there is no response in step  5003   c , the transmitter terminal waits until a timeout time elapses (step  5003   i ), and ends the processing after displaying there being no response (step  5003   j ). 
     Next, it is checked whether authentication processing has succeeded in step  5003   e , and when authentication processing has succeeded (Yes in step  5003   e ), if a command other than authentication is included in the ID indicated by light emission (Yes in step  5003   f ), processing in accordance with the command is performed (step  5003   g ). 
     It should be noted that if authentication fails in step  5003   e , an authentication error is displayed (step  5003   h ), and the processing ends. 
       FIG. 194  is a flowchart illustrating operation of the receiver terminal according to the present embodiment. The following is a description of  FIG. 194 . 
     First, a receiver terminal activates a camera in an optical authentication mode (step  5004   a ). 
     Next, it is checked whether light has been received in a specific pattern (step  5004   b ), and if it is determined that such light has been received (Yes in step  5004   b ), a receiver ID is created which can show that a transmitter ID has been received (step  5004   c ). It should be noted that if it is not determined that such light has been received (No in step  5004   b ), the receiver terminal waits until a timeout time elapses (Yes in step  5004   i ), and displays timeout (step  5004   j ), and the processing ends. 
     Next, it is checked whether the transmitter terminal holds an ID of the transmitter terminal (step  5004   k ), and if the transmitter terminal holds the ID of the terminal (Yes in step  5004   k ), the transmitter terminal unicasts the receiver ID to the terminal (step  5004   d ). On the other hand, if the transmitter terminal does not hold the ID of the terminal (No in step  5004   k ), the transmitter terminal broadcasts the receiver ID (step  50041 ). 
     Next, authentication processing is started by the transmission terminal (step  5004   e ), and if the authentication processing has succeeded (Yes in step  5004   e ), it is determined whether a command is included in the ID obtained by receiving light (step  5004   f ). If it is determined in step  5004   f  that a command is included (YES in step  5004   f ), processing according to the ID is performed (step  5004   g ). 
     It should be noted that if authentication fails in step  5004   e  (No in step  5004   e ), an authentication error is displayed (step  5004   h ), and the processing ends. 
     As described above, according to the present embodiment, the communication using visible light is used for wireless authentication, whereby it can be determined that a user to be authenticated is certainly in a room, and wireless authentication of a home electric appliance can be performed with ease and in a secured manner. 
     Embodiment 11 
     Although the flows for data exchange using NFC communication and high-speed wireless communication are described in the embodiments above, the present disclosure is not limited to those. An embodiment of the present disclosure can of course be achieved as the flows as illustrated in  FIGS. 195 to 197 , for example. 
       FIG. 195  is a sequence diagram in which a mobile AV terminal  1  transmits data to a mobile AV terminal  2  according to the present embodiment. Specifically,  FIG. 195  is a sequence diagram of data transmission and reception performed using NFC and wireless LAN communication. The following is a description of  FIG. 195 . 
     First, the mobile AV terminal  1  displays, on a screen, data to be transmitted to the mobile AV terminal  2 . 
     Here, if the mobile AV terminals  1  and  2  are brought into contact with each other to perform NFC communication, the mobile AV terminal  1  displays, on the screen, a confirmation screen for checking whether data transmission is to be performed. This confirmation screen may be a screen for requesting a user to select “Yes/No” together with the words “Transmit data?” or may be an interface for starting data transmission by the screen of the mobile AV terminal  1  being touched again. 
     In the case of “Yes” when it is checked whether data is intended to be transmitted, the mobile AV terminal  1  and the mobile AV terminal  2  exchange, by NFC communication, information on data to be transmitted and information for establishing high-speed wireless communication. The information on the data to be transmitted may be exchanged by wireless LAN communication. Information on establishment of wireless LAN communication may indicate a communication channel, or a service set identifier (SSID), and cryptographic key information, or may indicate a method of exchanging ID information created randomly and establishing a secure channel using this information 
     If wireless LAN communication is established, the mobile AV terminals  1  and  2  perform data communication by wireless LAN communication, and the mobile AV terminal  1  transmits the transmission target data thereof to the mobile AV terminal  2 . 
     Next, a description is given using  FIGS. 196 and 197 , focusing on changes of the screens of the mobile AV terminal  1  and the mobile AV terminal  2 .  FIG. 196  is a diagram illustrating a screen changed when the mobile AV terminal  1  transmits data to the mobile AV terminal  2  according to the present embodiment.  FIG. 197  is a diagram illustrating a screen changed when the mobile AV terminal  1  transmits data to the mobile AV terminal  2  according to the present embodiment. 
     In  FIGS. 196 and 197 , a user activates an application for reproducing video and a still image in the mobile AV terminal  1 , first. This application displays a still image and video data stored in the mobile AV terminal  1 . 
     Here, NFC communication is performed by bringing the mobile AV terminals  1  and  2  to be almost in contact with each other. This NFC communication is processing for starting exchange of a still image and video data in the mobile AV terminal  1 . 
     First, when the mobile AV terminals  1  and  2  recognize the start of data exchange by NFC communication, a confirmation screen for checking whether data is to be transmitted is displayed on the screen of the mobile AV terminal  1 . It should be noted that this confirmation screen may be an interface for facilitating a user to touch the screen to start data transmission or an interface for facilitating a user to select whether to allow data transmission by Yes/No, as in  FIG. 196 . In the case of Yes in determination as to whether data transmission is to be started, or specifically, when the mobile AV terminal  1  is to transmit data to the mobile AV terminal  2 , the mobile AV terminal  1  transmits, to the mobile AV terminal  2 , information on data to be exchanged and information on the start of high-speed wireless communication via a wireless LAN. It should be noted that information on this data to be exchanged may be transmitted using high-speed wireless communication. 
     Next, upon receipt and transmission of the information on the start of high-speed wireless communication via the wireless LAN, the mobile AV terminals  1  and  2  perform processing for establishing connection by wireless LAN communication. This processing includes determining which channel is to be used for communication, and which of the terminals is a parent terminal and which is a child terminal on communication topology, and exchanging password information, SSIDs of the terminals, and terminal information, for instance. 
     Next, when the connection by wireless LAN communication is established, the mobile AV terminals  1  and  2  transmit data by wireless LAN communication. During data transmission, the mobile AV terminal  1  displays, on the screen, video being reproduced normally, whereas the mobile AV terminal  2  which receives data displays, on the screen, data being received. This is because if the mobile AV terminal  1  displays data being transmitted on the screen, the mobile AV terminal  1  cannot perform other processing, and thus data is transmitted in the background, thereby achieving an advantage of the improvement of a user&#39;s convenience. In addition, the mobile AV terminal  2  which is receiving data displays data being received on the screen so that the received data can be immediately displayed, thereby achieving an advantage of displaying data immediately after reception of the data is completed. 
     Finally, the mobile AV terminal  2  displays the received data after the data reception is completed. 
       FIGS. 198 to 200  are system outline diagrams when the mobile AV terminal  1  is a digital camera according to the present embodiment. 
     As illustrated in  FIG. 198 , it is needless to say that the mobile phone according to the present embodiment is even applicable to the case where the mobile AV terminal  1  is a digital camera. 
     In addition, if the mobile AV terminal  1  is a digital camera, the digital camera does not have a means of the Internet access by mobile-phone communication in many cases, although typical digital cameras have a means of the Internet access by wireless LAN. 
     Accordingly, it is preferable to adopt a configuration in which as illustrated in  FIGS. 199 and 200 , the digital camera (the mobile AV terminal  1 ) transmits captured image data by a wireless LAN to picture sharing service in an environment where wireless LAN communication can be performed, whereas in an environment where wireless LAN communication cannot be performed, the digital camera transmits data to the mobile AV terminal  2  using a wireless LAN first, and the mobile AV terminal  2  transmits the as-is received data to picture sharing service by mobile phone communication. 
     Since wireless LAN communication is performed at a higher speed than mobile phone communication, a picture can be transmitted to picture sharing service at high speed by performing wireless LAN communication if possible. In addition, the service area of a mobile phone communication network is generally larger than a wireless LAN communication network, and thus if wireless LAN environment is not available, a function of transmitting data to picture sharing service by mobile phone communication via the mobile AV terminal  2  is provided, thereby allowing a picture to be immediately transmitted to picture sharing service at various places. 
     As described above, according to the present embodiment, data can be exchanged using NFC communication and high-speed wireless communication. 
     The above is a description of, for instance, an information communication device according to one or more aspects of the present disclosure based on the embodiments. The present disclosure, however, is not limited to the embodiments. Various modifications to the embodiments that may be conceived by those skilled in the art and combinations of constituent elements in different embodiments may be included within the scope of one or more aspects of the present disclosure, without departing from the spirit of the present disclosure. 
     It should be noted that in the above embodiments, each of the constituent elements may be constituted by dedicated hardware, or may be obtained by executing a software program suitable for the constituent element. Each constituent element may be achieved by a program execution unit such as a CPU or a processor reading and executing a software program stored in a recording medium such as a hard disk or semiconductor memory. 
     Embodiment 12 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as an LED blink pattern in Embodiments 1 to 11 described above. 
       FIG. 201  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7001   a  such as a signage of a restaurant transmits identification information (ID) of the transmitter  7001   a  to a receiver  7001   b  such as a smartphone. The receiver  7001   b  obtains information associated with the ID from a server, and displays the information. Examples of the information include a route to the restaurant, availability, and a coupon. 
       FIG. 202  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7042   b  such as a signage of a movie transmits identification information (ID) of the transmitter  7042   b  to a receiver  7042   a  such as a smartphone. The receiver  7042   a  obtains information associated with the ID from a server, and displays the information. Examples of the information include an image  7042   c  prompting to reserve a seat for the movie, an image  7042   d  showing scheduled times for the movie, an image  7042   e  showing availability, and an image  7042   f  notifying reservation completion. 
       FIG. 203  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7043   b  such as a signage of a drama transmits identification information (ID) of the transmitter  7043   b  to a receiver  7043   a  such as a smartphone. Having received the ID, the receiver  7043   a  obtains information associated with the ID from a server, and displays the information. Examples of the information include an image  7043   c  prompting to timer record the drama, an image  7043   d  prompting to select a recorder for recording the drama, and an image  7043   e  notifying timer recording completion. 
       FIG. 204  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7044   d  or  7044   c  such as a signage of a store, e.g. a roof sign or a sign placed on a street, transmits identification information (ID) of the transmitter  7044   d  or  7044   c  to a receiver  7044   a  such as a smartphone. The receiver  7044   a  obtains information associated with the ID from a server, and displays the information. Examples of the information include an image  7044   b  showing availability, a coupon, and the like of the store. 
       FIG. 205  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 12. This flowchart corresponds to the examples of application illustrated in  FIGS. 201 to 204 . 
     First, the ID of the transmitter and the information to be provided to the receiver receiving the ID are stored in the server in association with each other (Step  7101   a ). The information to be provided to the receiver may include information such as a store name, a product name, map information to a store, availability information, coupon information, stock count of a product, show time of a movie or a play, reservation information, and a URL of a server for reservation or purchase. 
     Next, the transmitter transmits the ID (Step  7101   b ). The camera of the receiver is pointed to the transmitter, to receive the ID (Step  7101   c ). 
     The receiver transmits the received ID to the server, and stores the information associated with the ID in the receiver (Step  7101   d ). 
     The receiver also stores a terminal ID and a user ID in the server (Step  7101   e ). The receiver displays the information stored in the server as the information to be displayed on the receiver (Step  7101   f ). 
     The receiver adjusts the display, based on a user profile stored in the receiver or the server (Step  7101   g ). For example, the receiver performs control such as changing the font size, hiding age-restricted content, or preferentially displaying content assumed to be preferred from the user&#39;s past behavior. 
     The receiver displays the route from the current position to the store or the sales floor (Step  7101   h ). The receiver obtains information from the server according to need, and updates and displays availability information or reservation information (Step  7101   i ). The receiver displays a button for storing the obtained information and a button for cancelling the storage of the displayed information (Step  7101   j ). 
     The user taps the button for storing the information obtained by the receiver (Step  7101   k ). The receiver stores the obtained information so as to be redisplayable by a user operation (Step  7101   m ). A reader in the store reads information transmitted from the receiver (Step  7101   n ). Examples of the transmission method include visible light communication, communication via Wi-Fi or Bluetooth, and communication using 2D barcode. The transmission information may include the ID of the receiver or the user ID. 
     The reader in the store stores the read information and an ID of the store in the server (Step  7101   p ). The server stores the transmitter, the receiver, and the store in association with each other (Step  7101   q ). This enables analysis of the advertising effectiveness of the signage. 
       FIG. 206  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7002   a  such as a signage of a plurality of stores transmits identification information (ID) of the transmitter  7002   a  to a receiver  7002   b  such as a smartphone. Having received the ID, the receiver  7002   b  obtains information associated with the ID from a server, and displays the same information as the signage. When the user selects a desired store by tapping or voice, the receiver  7002   b  displays the details of the store. 
       FIG. 207  is a flowchart illustrating an example of processing operation of the receiver  7002   b  and the transmitter  7002   a  in Embodiment 12. 
     The ID of the transmitter  7002   a  and the information to be provided to the receiver  7002   b  receiving the ID are stored in the server in association with each other (Step  7102   a ). The information to be provided to the receiver  7002   b  may include information such as a store name, a product name, map information to a store, availability information, coupon information, stock count of a product, show time of a movie or a play, reservation information, and a URL of a server for reservation or purchase. The position relation of information displayed on the transmitter  7002   a  is stored in the server. 
     The transmitter  7002   a  such as a signage transmits the ID (Step  7102   b ). The camera of the receiver  7002   b  is pointed to the transmitter  7002   a , to receive the ID (Step  7102   c ). The receiver  7002   b  transmits the received ID to the server, and obtains the information associated with the ID (Step  7102   d ). The receiver  7002   b  displays the information stored in the server as the information to be displayed on the receiver  7002   b  (Step  7102   e ). An image which is the information may be displayed on the receiver  7002   b  while maintaining the position relation of the image displayed on the transmitter  7002   a.    
     The user selects information displayed on the receiver  7002   b , by designation by screen tapping or voice (Step  7102   f ). The receiver  7002   b  displays the details of the information designated by the user (Step  7102   g ). 
       FIG. 208  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7003   a  such as a signage of a plurality of stores transmits identification information (ID) of the transmitter  7003   a  to a receiver  7003   b  such as a smartphone. Having received the ID, the receiver  7003   b  obtains information associated with the ID from a server, and displays information near (e.g. nearest) the center of the captured image of the camera of the receiver  7003   b  from among the information displayed on the signage. 
       FIG. 209  is a flowchart illustrating an example of processing operation of the receiver  7003   b  and the transmitter  7003   a  in Embodiment 12. 
     The ID of the transmitter  7003   a  and the information to be provided to the receiver  7003   b  receiving the ID are stored in the server in association with each other (Step  7103   a ). The information to be provided to the receiver  7003   b  may include information such as a store name, a product name, map information to a store, availability information, coupon information, stock count of a product, show time of a movie or a play, reservation information, and a URL of a server for reservation or purchase. The position relation of information displayed on the transmitter  7003   a  is stored in the server. 
     The transmitter  7003   a  such as a signage transmits the ID (Step  7103   b ). The camera of the receiver  7003   b  is pointed to the transmitter  7003   a , to receive the ID (Step  7103   c ). The receiver  7003   b  transmits the received ID to the server, and obtains the information associated with the ID (Step  7103   d ). The receiver  7003   b  displays information nearest the center of the captured image or the designated part from among the information displayed on the signage (Step  7103   e ). 
       FIG. 210  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7004   a  such as a signage of a plurality of stores transmits identification information (ID) of the transmitter  7004   a  to a receiver  7004   b  such as a smartphone. Having received the ID, the receiver  7004   b  obtains information associated with the ID from a server, and displays information (e.g. image showing the details of the store “B Cafe”) near the center of the captured image of the camera of the receiver  7004   b  from among the information displayed on the signage. When the user flicks left the screen, the receiver  7004   b  displays an image showing the details of the store “C Bookstore” on the right side of the store “B Cafe” on the signage. Thus, the receiver  7004   b  displays the image in the same position relation as that in the transmitter signage. 
       FIG. 211  is a flowchart illustrating an example of processing operation of the receiver  7004   b  and the transmitter  7004   a  in Embodiment 12. 
     The ID of the transmitter  7004   a  and the information to be provided to the receiver  7004   b  receiving the ID are stored in the server in association with each other (Step  7104   a ). The information to be provided to the receiver  7004   b  may include information such as a store name, a product name, map information to a store, availability information, coupon information, stock count of a product, show time of a movie or a play, reservation information, and a URL of a server for reservation or purchase. The position relation of information displayed on the transmitter  7004   a  is stored in the server. 
     The transmitter  7004   a  such as a signage transmits the ID (Step  7104   b ). The camera of the receiver  7004   b  is pointed to the transmitter  7004   a , to receive the ID (Step  7104   c ). The receiver  7004   b  transmits the received ID to the server, and obtains the information associated with the ID (Step  7104   d ). The receiver  7004   b  displays the information stored in the server as the information to be displayed on the receiver  7004   b  (Step  7104   e ). 
     The user performs a flick operation on the receiver  7004   b  (Step  7104   f ). The receiver  7004   b  changes the display in the same position relation as the information displayed on the transmitter  7004   a , according to the user operation (Step  7104   g ). For example, in the case where the user flicks left the screen to display the information on the right side of the currently displayed information, the information displayed on the transmitter  7004   a  on the right side of the information currently displayed on the receiver  7004   b  is displayed on the receiver  7004   b.    
       FIG. 212  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7005   a  such as a signage of a plurality of stores transmits identification information (ID) of the transmitter  7005   a  to a receiver  7005   b  such as a smartphone. Having received the ID, the receiver  7005   b  obtains information associated with the ID from a server, and displays information (e.g. Image showing the details of the store “B Cafe”) near the center of the captured image of the camera of the receiver  7005   b  from among the information displayed on the signage. When the user taps the left of the screen (or a left arrow on the screen) of the receiver  7005   b , the receiver  7005   b  displays an image showing the details of the store “A Restaurant” on the left side of the store “B Cafe” on the signage. When the user taps the bottom of the screen (or a down arrow on the screen) of the receiver  7005   b , the receiver  7005   b  displays an image showing the details of the store “E Office” below the store “B Cafe” on the signage. When the user taps the right of the screen (or a right arrow on the screen) of the receiver  7005   b , the receiver  7005   b  displays an image showing the details of the store “C Bookstore” on the left side of the store “B Cafe” on the signage. Thus, the receiver  7004   b  displays the image in the same position relation as that in the transmitter signage. 
       FIG. 213  is a flowchart illustrating an example of processing operation of the receiver  7005   b  and the transmitter  7005   a  in Embodiment 12. 
     The ID of the transmitter  7005   a  and the information to be provided to the receiver  7005   b  receiving the ID are stored in the server in association with each other (Step  7105   a ). The information to be provided to the receiver  7005   b  may include information such as a store name, a product name, map information to a store, availability information, coupon information, stock count of a product, show time of a movie or a play, reservation information, and a URL of a server for reservation or purchase. The position relation of information displayed on the transmitter  7005   a  is stored in the server. 
     The transmitter  7005   a  such as a signage transmits the ID (Step  7105   b ). The camera of the receiver  7005   b  is pointed to the transmitter  7005   a , to receive the ID (Step  7105   c ). The receiver  7005   b  transmits the received ID to the server, and obtains the information associated with the ID (Step  7105   d ). The receiver  7005   b  displays the information stored in the server as the information to be displayed on the receiver  7005   b  (Step  7105   e ). 
     The user taps the edge of the screen displayed on the receiver  7005   b  or the up, down, left, or right direction indicator displayed on the receiver  7005   b  (Step  7105   f ). The receiver changes the display in the same position relation as the information displayed on the transmitter  7005   a , according to the user operation. For example, in the case where the user taps the right of the screen or the right direction indicator on the screen, the information displayed on the transmitter  7005   a  on the right side of the information currently displayed on the receiver  7005   b  is displayed on the receiver  7005   b.    
       FIG. 214  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. A rear view of a vehicle is given in  FIG. 214 . 
     A transmitter (vehicle)  7006   a  having, for instance, two car taillights (light emitting units or lights) transmits identification information (ID) of the transmitter  7006   a  to a receiver such as a smartphone. Having received the ID, the receiver obtains information associated with the ID from a server. Examples of the information include the ID of the vehicle or the transmitter, the distance between the light emitting units, the size of the light emitting units, the size of the vehicle, the shape of the vehicle, the weight of the vehicle, the number of the vehicle, the traffic ahead, and information indicating the presence/absence of danger. The receiver may obtain these information directly from the transmitter  7006   a.    
       FIG. 215  is a flowchart illustrating an example of processing operation of the receiver and the transmitter  7006   a  in Embodiment 12. 
     The ID of the transmitter  7006   a  and the information to be provided to the receiver receiving the ID are stored in the server in association with each other (Step  7106   a ). The information to be provided to the receiver may include information such as the size of the light emitting unit as the transmitter  7006   a , the distance between the light emitting units, the shape and weight of the object including the transmitter  7006   a , the identification number such as a vehicle identification number, the state of an area not easily observable from the receiver, and the presence/absence of danger. 
     The transmitter  7006   a  transmits the ID (Step  7106   b ). The transmission information may include the URL of the server and the information to be stored in the server. 
     The receiver receives the transmitted information such as the ID (Step  7106   c ). The receiver obtains the information associated with the received ID from the server (Step  7106   d ). The receiver displays the received information and the information obtained from the server (Step  7106   e ). 
     The receiver calculates the distance between the receiver and the light emitting unit by triangulation, from the information of the size of the light emitting unit and the apparent size of the captured light emitting unit or from the information of the distance between the light emitting units and the distance between the captured light emitting units (Step  7106   f ). The receiver issues a warning of danger or the like, based on the information such as the state of an area not easily observable from the receiver and the presence/absence of danger (Step  7106   g ). 
       FIG. 216  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter (vehicle)  7007   b  having, for instance, two car taillights (light emitting units or lights) transmits information of the transmitter  7007   b  to a receiver  7007   a  such as a transmitter-receiver in a parking lot. The information of the transmitter  7007   b  indicates the identification information (ID) of the transmitter  7007   b , the number of the vehicle, the size of the vehicle, the shape of the vehicle, or the weight of the vehicle. Having received the information, the receiver  7007   a  transmits information of whether or not parking is permitted, charging information, or a parking position. The receiver  7007   a  may receive the ID, and obtain information other than the ID from the server. 
       FIG. 217  is a flowchart illustrating an example of processing operation of the receiver  7007   a  and the transmitter  7007   b  in Embodiment 12. Since the transmitter  7007   b  performs not only transmission but also reception, the transmitter  7007   b  includes an in-vehicle transmitter and an in-vehicle receiver. 
     The ID of the transmitter  7007   b  and the information to be provided to the receiver  7007   a  receiving the ID are stored in the server (parking lot management server) in association with each other (Step  7107   a ). The information to be provided to the receiver  7007   a  may include information such as the shape and weight of the object including the transmitter  7007   b , the identification number such as a vehicle identification number, the identification number of the user of the transmitter  7007   b , and payment information. 
     The transmitter  7007   b  (in-vehicle transmitter) transmits the ID (Step  7107   b ). The transmission information may include the URL of the server and the information to be stored in the server. The receiver  7007   a  (transmitter-receiver) in the parking lot transmits the received information to the server for managing the parking lot (parking lot management server) (Step  7107   c ). The parking lot management server obtains the information associated with the ID of the transmitter  7007   b , using the ID as a key (Step  7107   d ). The parking lot management server checks the availability of the parking lot (Step  7107   e ). 
     The receiver  7007   a  (transmitter-receiver) in the parking lot transmits information of whether or not parking is permitted, parking position information, or the address of the server holding these information (Step  7107   f ). Alternatively, the parking lot management server transmits these information to another server. The transmitter (in-vehicle receiver)  7007   b  receives the transmitted information (Step  7107   g ). Alternatively, the in-vehicle system obtains these information from another server. 
     The parking lot management server controls the parking lot to facilitate parking (Step  7107   h ). For example, the parking lot management server controls a multi-level parking lot. The transmitter-receiver in the parking lot transmits the ID (Step  7107   i ). The in-vehicle receiver (transmitter  7007   b ) inquires of the parking lot management server based on the user information of the in-vehicle receiver and the received ID (Step  7107   j ). 
     The parking lot management server charges for parking according to parking time and the like (Step  7107   k ). The parking lot management server controls the parking lot to facilitate access to the parked vehicle (Step  7107   m ). For example, the parking lot management server controls a multi-level parking lot. The in-vehicle receiver (transmitter  7007   b ) displays the map to the parking position, and navigates from the current position (Step  7107   n ). 
       FIG. 218  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7008   a  or  7008   b  such as a signage of a store, e.g. a roof sign or a sign placed on a street, transmits identification information (ID) of the transmitter  7008   a  or  7008   b  to a receiver  7008   c  such as a smartphone. Having received the ID, the receiver  7008   c  obtains information associated with the ID from a server, and displays the information. Examples of the information include an image showing availability, a coupon, 2D barcode, and the like of the store. 
       FIG. 219  is a flowchart illustrating an example of processing operation of the receiver  7008   c  and the transmitter  7008   a  or  7008   b  in Embodiment 12. Though the following describes, of the transmitters  7008   a  and  7008   b , the transmitter  7008   a  as an example, the processing operation of the transmitter  7008   b  is the same as that of the transmitter  7008   a.    
     The ID of the transmitter  7008   a  and the information to be provided to the receiver  7008   c  receiving the ID are stored in the server in association with each other (Step  7108   a ). The information to be provided to the receiver  7008   c  may include information such as a store name, a product name, map information to a store, availability information, coupon information, stock count of a product, show time of a movie or a play, reservation information, and a URL of a server for reservation or purchase. 
     The transmitter  7008   a  such as a signage transmits the ID (Step  7108   b ). The camera of the receiver  7008   c  is pointed to the transmitter  7008   a , to receive the ID (Step  7108   c ). The receiver  7008   c  transmits the received ID to the server, and stores the information associated with the ID in the receiver  7008   c  (Step  7108   d ). The receiver  7008   c  also stores a terminal ID and a user ID in the server (Step  7108   e ). 
     The receiver  7008   c  displays the information stored in the server as the information to be displayed on the receiver  7008   c  (Step  7108   f ). The receiver  7008   c  displays the route from the current position to the store or the sales floor (Step  7108   g ). The receiver  7008   c  obtains information from the server according to need, and updates and displays availability information or reservation information (Step  7108   h ). 
     The receiver  7008   c  displays a button for reserving or ordering a seat or a product (Step  7108   i ). The user taps the reserve button or the order button displayed on the receiver  7008   c  (Step  7108   j ). The receiver  7008   c  transmits the information of reservation or order to the server for managing reservation or order (Step  7108   k ). 
       FIG. 220  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A receiver (terminal)  7009   b  such as a smartphone is placed on a table in front of a seat in a store. A transmitter  7009   a  such as a lighting device transmits identification information (ID) of the transmitter  7009   a  to the receiver  7009   b . Having received the ID, the receiver  7009   b  obtains information associated with the ID from a server, and performs a process such as reserving the seat, confirming the provisional reservation, or extending the reserved time. 
       FIG. 221  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     Having obtained the information from the server, the receiver  7009   b  displays, for example, the availability of the store and buttons for selecting “check”, “extend”, and “additional order”. 
       FIG. 222  is a flowchart illustrating an example of processing operation of the receiver  7009   b  and the transmitter  7009   a  in Embodiment 12. 
     The ID of the transmitter  7009   a  and the information to be provided to the receiver  7009   b  receiving the ID are stored in the server in association with each other (Step  7109   a ). The information to be provided to the receiver  7009   b  may include information of the position and shape of the transmitter  7009   a . The transmitter  7009   a  such as a ceiling lighting transmits the ID (Step  7109   b ). 
     The user places the receiver  7009   b  on the table or the like (Step  7109   c ). The receiver  7009   b  recognizes the placement of the receiver  7009   b  on the table or the like from the information of the gyroscope or the 9-axis sensor, and starts the reception process (Step  7109   d ). The receiver  7009   b  identifies an upward facing camera from the upward direction of the 9-axis sensor, and receives the ID using the camera. 
     The camera of the receiver  7009   b  is pointed to the transmitter  7009   a , to receive the ID (Step  7109   e ). The receiver  7009   b  transmits the received ID to the server, and stores the information associated with the ID in the receiver  7009   b  (Step  7109   f ). The receiver  7009   b  estimates the position of the receiver  7009   b  (Step  7109   g ). 
     The receiver  7009   b  transmits the position of the receiver  7009   b  to the store management server (Step  7109   h ). The store management server specifies the seat of the table on which the receiver  7009   b  is placed (Step  7109   i ). The store management server transmits the seat number to the receiver  7009   b  (Step  7109   j ). 
       FIG. 223  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7011   a  such as a ceiling lighting transmits identification information (ID) of the transmitter  7011   a  to a receiver  7011   b  such as a smartphone. Having received the ID, the receiver  7011   b  obtains information associated with the ID from a server, and estimates (determines) the self-position. When the receiver  7011   b  is placed at an electronic device  7011   c , the receiver  7011   b  functions as an operation terminal of the electronic device  7011   c . Thus, the electronic device  7011   c  can be operated by a rich interface such as a touch panel or voice output. 
       FIG. 224  is a flowchart illustrating an example of processing operation of the receiver  7011   b  and the transmitter  7011   a  in Embodiment 12. 
     The position of the electronic device is stored in the server (Step  7110   a ). The ID, model, function, and operation interface information (screen, input/output voice, interactive model) of the electronic device may be stored in association with the position information. 
     The ID of the transmitter  7011   a  and the information to be provided to the receiver  7011   b  receiving the ID are stored in the server in association with each other (Step  7110   b ). The information to be provided to the receiver  7011   b  may include information of the position and shape of the transmitter  7011   a.    
     The transmitter  7011   a  such as a ceiling lighting transmits the ID (Step  7110   c ). The camera of the receiver  7011   b  is pointed to the transmitter  7011   a , to receive the ID (Step  7110   d ). The receiver  7011   b  transmits the received ID to the server, and stores the information associated with the ID in the receiver  7011   b  (Step  7110   e ). The receiver  7011   b  estimates the position of the receiver  7011   b  (Step  7110   f ). 
     The user places the receiver  7011   b  at the electronic device (Step  7110   g ). The receiver  7011   b  recognizes that the receiver  7011   b  is stationary from the information of the gyroscope or the 9-axis sensor, and starts the following process (Step  7110   h ). The receiver  7011   b  estimates the self-position by the above-mentioned method, in the case where at least a predetermined time has elapsed from the last estimation of the position of the receiver  7011   b  (Step  7110   i ). 
     The receiver  7011   b  estimates the movement from the last self-position estimation from the information of the gyroscope or the 9-axis sensor, and estimates the current position (Step  7110   j ). The receiver  7011   b  obtains information of an electronic device nearest the current position, from the server (Step  7110   k ). The receiver  7011   b  obtains the information of the electronic device from the electronic device via Bluetooth or Wi-Fi (Step  7110   m ). Alternatively, the receiver  7011   b  obtains the information of the electronic device stored in the server. 
     The receiver  7011   b  displays the information of the electronic device (Step  7110   n ). The receiver  7011   b  receives input as the operation terminal of the electronic device (Step  7110   p ). The receiver  7011   b  transmits the operation information of the electronic device to the electronic device via Bluetooth or Wi-Fi (Step  7110   q ). Alternatively, the receiver  7011   b  transmits the operation information of the electronic device to the electronic device via the server. 
       FIG. 225  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A camera of a receiver  7012   a  such as a smartphone is pointed to a transmitter  7012   b  as an electronic device such as a television receiver (TV). The receiver  7012   a  receives identification information (ID) of the transmitter  7043   b  transmitted from the transmitter  7043   b . The receiver  7043   a  obtains information associated with the ID from a server. Thus, the receiver  7012   a  functions as an operation terminal of the electronic device in the direction pointed by the camera. That is, the receiver  7012   a  wirelessly connects to the transmitter  7012   b  via Bluetooth, WI-FI, or the like. 
       FIG. 226  is a flowchart illustrating an example of processing operation of the receiver  7012   a  and the transmitter  7012   b  in Embodiment 12. 
     The ID of the transmitter  7012   b  and the information to be provided to the receiver  7012   a  receiving the ID are stored in the server in association with each other (Step  7111   a ). The information to be provided to the receiver  7012   a  may include the ID, model, function, and operation interface information (screen, input/output voice, interactive model) of the electronic device. 
     The transmitter  7012   b  included in the electronic device or associated with the electronic device transmits the ID (Step  7111   b ). The camera of the receiver  7012   a  is pointed to the transmitter  7012   b , to receive the ID (Step  7111   c ). The receiver  7012   a  transmits the received ID to the server, and stores the information associated with the ID in the receiver  7012   a  (Step  7111   d ). The receiver  7012   a  obtains the information of the electronic device from the server, using the received ID as a key (Step  7111   e ). 
     The receiver  7012   a  obtains the information of the electronic device from the electronic device via Bluetooth or Wi-Fi (Step  7111   f ). Alternatively, the receiver  7012   a  obtains the information of the electronic device stored in the server. The receiver  7012   a  displays the information of the electronic device (Step  7111   g ). 
     The receiver  7012   a  receives input as the operation terminal of the electronic device (Step  7111   h ). The receiver  7012   a  transmits the operation information of the electronic device to the electronic device via Bluetooth or Wi-Fi (Step  7111   i ). Alternatively, the receiver  7012   a  transmits the operation information of the electronic device to the electronic device via the server. 
       FIG. 227  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A receiver  7013   b  such as a smartphone receives a destination input by the user. The camera of the receiver  7013   b  is then pointed to a transmitter  7013   a  such as a lighting device (light). The receiver  7013   b  receives identification information (ID) of the transmitter  7013   a  transmitted from the transmitter  7013   a . The receiver  7013   b  obtains information associated with the ID from a server. The receiver  7013   b  estimates (determines) the self-position based on the obtained information. The receiver  7013   b  accordingly navigates the user to the destination by audio or the like. In the case where the user is visually impaired, the receiver  7013   b  reports any obstacle to the user in detail. 
       FIG. 228  is a flowchart illustrating an example of processing operation of the receiver  7013   b  and the transmitter  7013   a  in Embodiment 12. 
     The user inputs the destination to the receiver  7013   b  (Step  7112   a ). The user points the receiver  7013   b  to the light (transmitter  7013   a ) (Step  7112   b ). Even a visually impaired user can point the receiver  7013   b  to the light if he or she is capable of recognizing intense light. 
     The receiver  7013   b  receives a signal superimposed on the light (Step  7112   c ). The receiver  7013   b  obtains information from the server, using the received signal as a key (Step  7112   d ). The receiver  7013   b  obtains a map from the current position to the destination from the server (Step  7112   e ). The receiver  7013   b  displays the map, and navigates from the current position to the destination (Step  7112   f ). 
       FIG. 229  is a diagram illustrating a state of the receiver in Embodiment 12. 
     A receiver (terminal)  7014   a  such as a smartphone includes a face camera  7014   b . When the imaging direction of the face camera  7014   b  is upward at a predetermined angle or more with the ground plane, the receiver  7014   a  performs a signal reception process (process of receiving a signal from a transmitter by imaging) by the face camera  7014   b . In the case where the receiver  7014   a  also includes a camera other than the face camera  7014   b , the receiver  7014   a  assigns higher priority to the face camera  7014   b  than the other camera. 
       FIG. 230  is a flowchart illustrating an example of processing operation of the receiver  7014   a  in Embodiment 12. 
     The receiver  7014   a  determines whether or not the imaging direction of the face camera  7014   b  is upward at a predetermined angle or more with the ground plane (Step  7113   a ). In the case where the determination result is true (Y), the receiver  7014   a  starts the reception by the face camera  7014   b  (Step  7113   b ). Alternatively, the receiver  7014   a  assigns higher priority to the reception process by the face camera  7014   b . When a predetermined time has elapsed (Step  7113   c ), the receiver  7014   a  ends the reception by the face camera  7014   b  (Step  7113   d ). Alternatively, the receiver  7014   a  assigns lower priority to the reception process by the face camera  7014   b.    
       FIG. 231  is a diagram illustrating a state of the receiver in Embodiment 12. 
     A receiver (terminal)  7015   a  such as a smartphone includes an out camera  7015   b . When the imaging direction of the out camera  7015   b  is at a predetermined angle or less with the ground plane, the receiver  7014   a  performs a signal reception process (process of receiving a signal from a transmitter by imaging) by the out camera  7015   b . In the case where the receiver  7015   a  also includes a camera other than the out camera  7015   b , the receiver  7015   a  assigns higher priority to the out camera  7015   b  than the other camera. 
     Note that, when the imaging direction of the out camera  7015   b  is at a predetermined angle or less with the ground plane, the receiver  7015   a  is in portrait orientation, and the surface of the receiver  7015   a  on which the out camera  7015   b  is provided is at a predetermined angle or more with the ground plane. 
       FIG. 232  is a flowchart illustrating an example of processing operation of the receiver  7015   a  in Embodiment 12. 
     The receiver  7015   a  determines whether or not the imaging direction of the out camera  7015   b  is at a predetermined angle or less with the ground plane (Step  7114   a ). In the case where the determination result is true (Y), the receiver  7015   a  starts the reception by the out camera  7015   b  (Step  7114   b ). Alternatively, the receiver  7015   a  assigns higher priority to the reception process by the out camera  7015   b . When a predetermined time has elapsed (Step  7114   c ), the receiver  7015   a  ends the reception by the out camera  7015   b  (Step  7114   d ). Alternatively, the receiver  7015   a  assigns lower priority to the reception process by the out camera  7015   b.    
       FIG. 233  is a diagram illustrating a state of the receiver in Embodiment 12. 
     A receiver (terminal)  7016   a  such as a smartphone includes an out camera. When the receiver  7016   a  is moved (stuck out) in the imaging direction of the out camera, the receiver  7016   a  performs a signal reception process (process of receiving a signal from a transmitter by imaging) by the out camera. In the case where the receiver  7016   a  also includes a camera other than the out camera, the receiver  7016   a  assigns higher priority to the out camera than the other camera. 
     Note that, when the receiver  7016   a  is moved in the imaging direction of the out camera, the angle between the moving direction and the imaging direction (upon the end of the movement) is a predetermined angle or less. 
       FIG. 234  is a flowchart illustrating an example of processing operation of the receiver  7016   a  in Embodiment 12. 
     The receiver  7016   a  determines whether or not the receiver  7016   a  is moved and the angle between the moving direction and the imaging direction of the out camera upon the end of the movement is a predetermined angle or less (Step  7115   a ). In the case where the determination result is true (Y), the receiver  7016   a  starts the reception by the out camera (Step  7115   b ). Alternatively, the receiver  7016   a  assigns higher priority to the reception process by the out camera. When a predetermined time has elapsed (Step  7115   c ), the receiver  7016   a  ends the reception by the out camera (Step  7115   d ). Alternatively, the receiver  7016   a  assigns lower priority to the reception process by the out camera. 
       FIG. 235  is a diagram illustrating a state of the receiver in Embodiment 12. 
     A receiver (terminal)  7017   a  such as a smartphone includes a predetermined camera. When a display operation or specific button press corresponding to the predetermined camera is performed, the receiver  7017   a  performs a signal reception process (process of receiving a signal from a transmitter by imaging) by the predetermined camera. In the case where the receiver  7017   a  also includes a camera other than the predetermined camera, the receiver  7017   a  assigns higher priority to the predetermined camera than the other camera. 
       FIG. 236  is a flowchart illustrating an example of processing operation of the receiver  7017   a  in Embodiment 12. 
     The receiver  7017   a  determines whether or not a display operation or a specific button press is performed on the receiver  7017   a  (Step  7115   h ). In the case where the determination result is true (Y), the receiver  7017   a  starts the reception by the camera corresponding to the display operation or the specific button press (Step  7115   i ). Alternatively, the receiver  7017   a  assigns higher priority to the reception process by the camera. When a predetermined time has elapsed (Step  7115   j ), the receiver  7017   a  ends the reception by the camera corresponding to the display operation or the specific button press (Step  7115   k ). Alternatively, the receiver  7017   a  assigns lower priority to the reception process by the camera. 
       FIG. 237  is a diagram illustrating a state of the receiver in Embodiment 12. 
     A receiver (terminal)  7018   a  such as a smartphone includes a face camera  7018   b . When the imaging direction of the face camera  7018   b  is upward at a predetermined angle or more with the ground plane and also the receiver  7014   a  is moving along a direction at a predetermined angle or less with the ground plane, the receiver  7018   a  performs a signal reception process (process of receiving a signal from a transmitter by imaging) by the face camera  7018   b . In the case where the receiver  7018   a  also includes a camera other than the face camera  7018   b , the receiver  7018   a  assigns higher priority to the face camera  7018   b  than the other camera. 
       FIG. 238  is a flowchart illustrating an example of processing operation of the receiver  7018   a  in Embodiment 12. 
     The receiver  7018   a  determines whether or not the imaging direction of the face camera  7018   b  is upward at a predetermined angle or more with the ground plane and the receiver  7018   a  is translated at a predetermined angle or less with the ground plane (Step  7116   a ). In the case where the determination result is true (Y), the receiver  7018   a  starts the reception by the face camera  7018   b  (Step  7116   b ). Alternatively, the receiver  7018   a  assigns higher priority to the reception process by the face camera  7018   b . When a predetermined time has elapsed (Step  7116   c ), the receiver  7018   a  ends the reception by the face camera  7018   b  (Step  7116   d ). Alternatively, the receiver  7018   a  assigns lower priority to the reception process by the face camera  7018   b.    
       FIG. 239  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A camera of a receiver  7019   b  such as a smartphone is pointed to a transmitter  7019   a  as an electronic device such as a television receiver (TV). The receiver  7019   b  receives identification information (ID) of a currently viewed channel, which is transmitted from the transmitter  7019   a  (the display of the transmitter  7019   a ). The receiver  7019   b  obtains information associated with the ID from a server. Thus, the receiver  7019   b  displays a page for buying a related product of the TV program, or related information of the TV program. The receiver  7019   b  also participates in the TV program through voting or applying for presents. The transmitter (TV)  7019   a  may include an address storage unit storing the address of the user, and transmit information relating to the address stored in the address storage unit. The receiver  7019   b  transmits the received ID and the time of receiving the ID, to the server. By doing so, the receiver  7019   b  can obtain data from the server, without being affected by a delay from ID reception to server access. The transmitter  7019   a  may obtain, from a built-in clock or a broadcast wave, time information or an ID that changes with time, and transmit it. This enables the server to transmit data set by the broadcaster to the receiver, regardless of the time setting in the receiver. 
       FIG. 240  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     As illustrated in (a) in  FIG. 240 , the transmitter  7019   a  and the receiver  7019   b  may directly transmit and receive the information necessary for realizing the example of application illustrated in  FIG. 239 . 
     As illustrated in (b) in  FIG. 240 , the transmitter  7019   a  may transmit the ID of the currently viewed channel to the receiver  7019   b . In this case, the receiver  7019   b  receives the information associated with the ID, i.e. the information necessary for realizing the example of application illustrated in  FIG. 239 , from the server. 
     As illustrated in (c) in  FIG. 240 , the transmitter  7019   a  may transmit the ID of the transmitter (TV)  7019   a  or information necessary for wireless connection to the receiver  7019   b . In this case, the receiver  7019   b  receives the ID or the information, and inquires of the transmitter  7019   a  or a recorder for the currently viewed channel, based on the ID or the information. The receiver  7019   b  then obtains the information relating to the channel identified as a result of the inquiry, i.e. the information necessary for realizing the example of application illustrated in  FIG. 239 , from the server. 
     For example, the transmitter  7019   a  transmits an SSID (Service Set Identifier), a password, an IP address, a device ID, or the like, as the information necessary for wireless connection such as Wi-Fi or Bluetooth®. Having received such information, the receiver  7019   b  wirelessly connects to the transmitter  7019   a  based on the information. The receiver  7019   b  then obtains the information of the program viewed by the user from the transmitter  7019   a  via the wireless connection, and transmits the information of the program to the server. Having received the information of the program, the server transmits content held in association with the information of the program, to the receiver  7019   b . The receiver  7019   b  obtains the content from the server, and displays the content. 
       FIG. 241  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     The transmitter  7019   a  may include a TV  2021   b  and a recorder  2021   a . In the transmitter  7019   a , the recorder  2021   a  stores the identification information (ID) and the recording time of the recorded channel, upon recording. Alternatively, the recorder  2021   a  obtains, from the server, information associated with the identification information (ID) and the recording time of the recorded channel, and stores the obtained information. Upon reproduction, the TV  2021   b  transmits part or all of the information stored in the recorder  2021   a , to the receiver  7019   b . Moreover, at least one of the TV  2021   b  and the recorder  2021   a  may act as the server. In the case where the recorder  2021   a  acts as the server, the recorder  2021   a  replaces the server address with the address of the recorder  2021   a , and has the TV  202   b  transmit the address to the receiver  7019   b.    
       FIG. 242  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A camera of a receiver  7022   c  such as a smartphone is pointed to a transmitter  7022   b  as an electronic device such as a television receiver (TV). The receiver  7022   c  receives information transmitted from the transmitter  7022   b  (display of the transmitter  7022   b ). The receiver  7022   c  performs wireless communication with the transmitter  7022   b , based on the information. When the transmitter  7022   b  obtains information including an image to be displayed on the receiver  7022   c  from a server  7022   a  and transmits the information to the receiver  7022   c , the transmitter  7022   b  replaces the address of the server  7022   a  included in the information with the address of the transmitter  7022   b.    
       FIG. 243  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     For instance, a recorder  7023   b  obtains all of the information necessary for realizing the example of application illustrated in  FIG. 239  from a server  7023   a , upon recording a TV program. 
     Upon reproducing the TV program, the recorder  7023   b  transmits the reproduction screen and the information necessary for realizing the example of application illustrated in  FIG. 239 , to a TV  7023   c  as a transmitter. The TV  7023   c  receives the reproduction screen and the information, displays the reproduction image, and also transmits the information from the display. A receiver  7023   d  such as a smartphone receives the information, and performs wireless communication with the TV  7023   c  based on the information. 
     As an alternative, upon reproducing the TV program, the recorder  7023   b  transmits the reproduction screen and the information necessary for wireless communication such as the address of the recorder  7023   b , to the TV  7023   c  as a transmitter. The TV  7023   c  receives the reproduction screen and the information, displays the reproduction image, and also transmits the information from the display. The receiver  7023   d  such as a smartphone receives the information, and performs wireless communication with the recorder  7023   b  based on the information. 
       FIG. 244  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A camera of a receiver  7045   a  such as a smartphone is pointed to a transmitter  7045   b  as an electronic device such as a television receiver (TV). The transmitter  7045   b  displays video of a TV program such as a music program, and transmits information from the display. The receiver  7045   a  receives the information transmitted from the transmitter  7045   b  (display of the transmitter  7045   b ). The receiver  7045   a  displays a screen  7045   c  prompting to buy a song in the music program, based on the information. 
       FIG. 245  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 12. This flowchart corresponds to the examples of application illustrated in  FIGS. 239 to 244 . 
     The transmitter included in the TV or the recorder obtains, from the server, the information to be provided to the receiver as the information relating to the currently broadcasted program (Step  7117   a ). The transmitter transmits the signal by superimposing the signal on the backlight of the display (Step  7117   b ). The transmission signal may include a URL of the transmitter, an SSID of the transmitter, and a password for accessing the transmitter. 
       FIG. 246  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 12. This flowchart corresponds to the examples of application illustrated in  FIGS. 239 to 244 . 
     The receiver receives the information from the display (Step  7118   a ). The receiver determines whether or not the currently viewed channel information is included in the received information (Step  7118   b ). In the case where the determination result is false (N), the receiver obtains the currently viewed channel information from the electronic device having the ID included in the received information (Step  7118   c ). 
     In the case where the determination result is true (Y), the receiver obtains the information related to the currently viewed screen from the server (Step  7118   d ). The TV or the recorder may act as the server. The receiver displays the information obtained from the server (Step  7118   e ). The receiver adjusts the display, based on a user profile stored in the receiver or the server (Step  7118   f ). For example, the receiver performs control such as changing the font size, hiding age-restricted content, or preferentially displaying content assumed to be preferred from the user&#39;s past behavior. 
       FIG. 247  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 12. This flowchart corresponds to the examples of application illustrated in  FIGS. 239 to 244 . 
     The recorder obtains the information related to the program from the server and stores the information, when recording the program (Step  7119   a ). In the case where the related information changes with time, the recorder also stores the time. 
     The recorder transmits the stored information to the display, when reproducing the recorded image (Step  7119   b ). The access information (URL or password) of the server in the stored information may be replaced with the access information of the display. 
     The recorder transmits the stored information to the receiver, when reproducing the recorded image (Step  7119   c ). The access information (URL or password) of the server in the stored information may be replaced with the access information of the recorder. 
       FIG. 248  is a diagram illustrating a luminance change of the transmitter in Embodiment 12. 
     The transmitter codes the information transmitted to the receiver, by making the time length from a rapid rise in luminance to the next rapid rise in luminance different depending on code (0 or 1). In this way, the brightness perceived by humans can be adjusted by PWM (Pulse Width Modulation) control, without changing the transmission information. Here, the luminance waveform may not necessarily be a precise rectangular wave. 
       FIG. 249  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. This flowchart illustrates the processing operation of the receiver that corresponds to the transmitter having the luminance change illustrated in  FIG. 248 . 
     The receiver observes the luminance of light emitted from the transmitter (Step  7120   a ). The receiver measures the time from a rapid rise in luminance to the next rapid rise in luminance (Step  7120   b ). Alternatively, the receiver measures the time from a rapid fall in luminance to the next rapid fall in luminance. The receiver recognizes the signal value according to the time (Step  7120   c ). For example, the receiver recognizes “0” in the case where the time is less than or equal to 300 microseconds, and “1” in the case where the time is greater than or equal to 300 microseconds. 
       FIG. 250  is a diagram illustrating a luminance change of the transmitter in Embodiment 12. 
     The transmitter expresses the starting point of the information transmitted to the receiver, by changing the wavelength indicating luminance rise/fall. Alternatively, the transmitter superimposes information on the other information, by changing the wavelength. 
       FIG. 251  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. This flowchart illustrates the processing operation of the receiver that corresponds to the transmitter having the luminance change illustrated in  FIG. 250 . 
     The receiver observes the luminance of light emitted from the transmitter (Step  7121   a ). The receiver determines the minimum value of the time width of the rapid change in luminance (Step  7121   b ). The receiver searches for a luminance change width that is not an integral multiple of the minimum value (Step  7121   c ). The receiver analyzes the signal, with the luminance change width that is not the integral multiple as the starting point (Step  7121   d ). The receiver calculates the time width between the parts each having the luminance change width that is not the integral multiple (Step  7121   e ). 
       FIG. 252  is a diagram illustrating a luminance change of the transmitter in Embodiment 12. 
     The transmitter can adjust the brightness perceived by the human eye and also reset any luminance change accumulated over time, by changing the luminance at intervals shorter than the exposure time of the receiver. 
       FIG. 253  is a flowchart illustrating an example of processing operation of the transmitter in Embodiment 12. This flowchart illustrates the processing operation of the receiver that corresponds to the transmitter having the luminance change illustrated in  FIG. 252 . 
     The transmitter turns the current ON/OFF with a time width sufficiently shorter than the exposure time of the receiver, when the luminance or the current for controlling the luminance falls below a predetermined value (Step  7125   a ). This returns the current to its initial value, so that the luminance decrease of the light emitting unit can be prevented. The transmitter turns the current ON/OFF with a time width sufficiently shorter than the exposure time of the receiver, when the luminance or the current for controlling the luminance exceeds a predetermined value (Step  7125   b ). This returns the current to its initial value, so that the luminance increase of the light emitting unit can be prevented. 
       FIG. 254  is a diagram illustrating a luminance change of the transmitter in Embodiment 12. 
     The transmitter expresses different signals (information), by making the carrier frequency of the luminance different. The receiver is capable of recognizing the carrier frequency earlier than the contents of the signal. Hence, making the carrier frequency different is suitable for expressing information, such as the ID of the transmitter, which needs to be recognized with priority. 
       FIG. 255  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. This flowchart illustrates the processing operation of the receiver that corresponds to the transmitter having the luminance change illustrated in  FIG. 254 . 
     The receiver observes the luminance of light emitted from the transmitter (Step  7122   a ). The receiver determines the minimum value of the time width of the rapid change in luminance (Step  7122   b ). The receiver recognizes the minimum value as the carrier frequency (Step  7122   c ). The receiver obtains information from the server, using the carrier frequency as a key (Step  7122   d ). 
       FIG. 256  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. This flowchart illustrates the processing operation of the receiver that corresponds to the transmitter having the luminance change illustrated in  FIG. 254 . 
     The receiver observes the luminance of light emitted from the transmitter (Step  7123   a ). The receiver Fourier transforms the luminance change, and recognizes the maximum component as the carrier frequency (Step  7123   b ). The receiver obtains information from the server, using the carrier frequency as a key (Step  7123   c ). 
       FIG. 257  is a flowchart illustrating an example of processing operation of the transmitter in Embodiment 12. This flowchart illustrates the processing operation of the transmitter having the luminance change illustrated in  FIG. 254 . 
     The transmitter expresses the transmission signal as the luminance change (Step  7124   a ). The transmitter generates the luminance change so that the maximum component of the Fourier transformed luminance change is the carrier frequency (Step  7124   b ). The transmitter causes the light emitting unit to emit light according to the generated luminance change (Step  7124   c ). 
       FIG. 258  is a diagram illustrating an example of a structure of the transmitter in Embodiment 12. 
     A transmitter  7028   a  has a part  7028   b  transmitting a signal A, a part  7028   d  transmitting a signal B, and a part  7028   f  transmitting a signal C. When such parts transmitting different signals are provided in the transmitter along the direction in which the imaging unit (camera) of the receiver is exposed simultaneously, the receiver can receive a plurality of signals simultaneously. Here, a part transmitting no signal or a buffer part  7028   c  or  7028   e  transmitting a special signal may be provided between the parts  7028   b ,  7028   d , and  7028   f.    
       FIG. 259  is a diagram illustrating an example of a structure of the transmitter in Embodiment 12. The system of light emission by this structure of the transmitter extends the system of light emission by the structure illustrated in  FIG. 258 . 
     Parts  7029   a  transmitting the signals illustrated in  FIG. 258  may be arranged in the transmitter as illustrated in  FIG. 259 . By doing so, even when the receiver is tilted, the imaging unit (camera) of the receiver can simultaneously receive (capture) many parts of the signals A, B, and C. 
       FIG. 260  is a diagram illustrating an example of a structure of the transmitter in Embodiment 12. The system of light emission by this structure of the transmitter extends the system of light emission by the structure illustrated in  FIG. 258 . 
     A circular light emitting unit of the transmitter has a plurality of annular parts  7030   a ,  7030   b , and  7030   c  arranged concentrically and transmitting the respective signals. The part  7030   a  transmits the signal C, the part  7030   b  transmits the signal B, and the part  7030   c  transmits the signal A. In the case where the light emitting unit of the transmitter is circular as in this example, the above-mentioned arrangement of the parts transmitting the respective signals enables the receiver to simultaneously receive (capture) many parts of the signals A, B, and C transmitted from the corresponding parts. 
       FIG. 261  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 12. This flowchart illustrates the processing operation of the receiver and the transmitter that includes the light emitting device illustrated in any of  FIGS. 258 to 260 . 
     The receiver measures the luminance of each position of the line that receives light simultaneously (Step  7126   a ). The receiver receives the signal at high speed, by receiving the separately transmitted signals in the direction perpendicular to the simultaneous light receiving line (Step  7126   b ). 
       FIG. 262  is a diagram illustrating an example of display and imaging by the receiver and the transmitter in Embodiment 12. 
     The transmitter displays a plurality of 1D barcodes each formed as an image uniform in the direction perpendicular to the direction in which the receiving unit (camera) of the receiver is exposed simultaneously, respectively as a frame 1 ( 7031   a ), a frame 2 ( 7031   b ), and a frame 3 ( 7031   c ) in sequence. A 1D barcode mentioned here is made of a line (bar) along the direction perpendicular to the above-mentioned simultaneous exposure direction. The receiver captures the image displayed on the transmitter as described in each of the above embodiments, and as a result obtains a frame 1 ( 7031   d ) and a frame 2 ( 7031   e ). The receiver can recognize the successively displayed 1D barcodes in sequence, by dividing the 1D barcodes at an interruption of the bar of each 1D barcode. In this case, the receiver can recognize all information displayed on the transmitter, with there being no need to synchronize the imaging by the receiver to the display by the transmitter. The display by the transmitter may be at a higher frame rate than the imaging by the receiver. The display time of one frame in the display by the transmitter, however, needs to be longer than the blanking time between the frames captured by the receiver. 
       FIG. 263  is a flowchart illustrating an example of processing operation of the transmitter in Embodiment 12. This flowchart illustrates the processing operation of the display device in the transmitter for performing the display illustrated in  FIG. 262 . 
     The display device displays a 1D barcode (Step  7127   a ). The display device changes the barcode display at intervals longer than the blanking time in the imaging by the receiver (Step  7127   b ). 
       FIG. 264  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. This flowchart illustrates the processing operation of the receiver for performing the imaging illustrated in  FIG. 262 . 
     The receiver captures the 1D barcode displayed on the display device (Step  7128   a ). The receiver recognizes that the display device displays the next barcode, at an interruption of the barcode line (Step  7128   b ). According to this method, the receiver can receive all displayed information, without synchronizing the imaging to the display. Besides, the receiver can receive the signal displayed at a frame rate higher than the imaging frame rate of the receiver. 
       FIG. 265  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     A transmitter  7032   a  such as a lighting device transmits encrypted identification information (ID) of the transmitter  7032   a . A receiver  7032   b  such as a smartphone receives the encrypted ID, and transmits the encrypted ID to a server  7032   c . The server  7032   c  receives the encrypted ID, and decrypts the encrypted ID. Alternatively, the receiver  7032   b  receives the encrypted ID, decrypts the encrypted ID, and transmits the decrypted ID to the server  7032   c.    
       FIG. 266  is a flowchart illustrating an example of processing operation of the receiver  7032   b  and the transmitter  7032   a  in Embodiment 12. 
     The transmitter  7032   a  holds partially or wholly encrypted information (Step  7129   a ). The receiver  7032   b  receives the information transmitted from the transmitter  7032   a , and decrypts the received information (Step  7129   b ). Alternatively, the receiver  7032   b  transmits the encrypted information to the server  7032   c . In the case where the encrypted information is transmitted, the server  7032   c  decrypts the encrypted information (Step  7129   c ). 
       FIG. 267  is a diagram illustrating a state of the receiver in Embodiment 12. 
     For a phone call, the user puts a receiver  7033   a  such as a smartphone to his or her ear. At this time, an illuminance sensor provided near the speaker of the receiver  7033   a  detects an illuminance value indicating low illuminance. The receiver  7033   a  accordingly estimates that the receiver  7033   a  is in a call state, and stops receiving information from the transmitter. 
       FIG. 268  is a flowchart illustrating an example of processing operation of the receiver  7033   a  in Embodiment 12. 
     The receiver  7033   a  determines whether or not the receiver  7033   a  is estimated to be in a call state from the sensor value of the illuminance sensor and the like (Step  7130   a ). In the case where the determination result is true (Y), the receiver  7033   a  ends the reception by the face camera (Step  7130   b ). Alternatively, the receiver  7033   a  assigns lower priority to the reception process by the face camera. 
       FIG. 269  is a diagram illustrating a state of the receiver in Embodiment 12. 
     A receiver  7034   a  such as a smartphone includes an illuminance sensor  7034   b  near a camera (e.g. face camera) which is an imaging device for receiving (capturing) information from a transmitter. When an illuminance value indicating low illuminance less than or equal to a predetermined value is detected by the illuminance sensor  7034   b , the receiver  7034   a  stops receiving information from the transmitter. In the case where the receiver  7034   a  includes a camera other than the camera (e.g. face camera) near the illuminance sensor  7034   b , the receiver  7034   a  assigns lower priority to the camera (e.g. face camera) near the illuminance sensor  7034   b  than the other camera. 
       FIG. 270  is a flowchart illustrating an example of processing operation of the receiver  7034   a  in Embodiment 12. 
     The receiver  7034   a  determines whether or not the sensor value of the illuminance sensor  7034   b  is less than or equal to a predetermined value (Step  7131   a ). In the case where the determination result is true (Y), the receiver  7034   a  ends the reception by the face camera (Step  7131   b ). Alternatively, the receiver  7034   a  assigns lower priority to the reception process by the face camera. 
       FIG. 271  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. 
     The receiver measures the illuminance change from the sensor value of the illuminance sensor (Step  7132   a ). The receiver receives the signal from the illuminance change, as in the reception of the signal from the luminance change measured by the imaging device (camera) (Step  7132   b ). Since the illuminance sensor is less expensive than the imaging device, the receiver can be manufactured at low cost. 
       FIG. 272  is a diagram illustrating an example of a wavelength of the transmitter in Embodiment 12. 
     The transmitter expresses the information transmitted to the receiver, by outputting metameric light  7037   a  and  7037   b  as illustrated in (a) and (b) in  FIG. 272 . 
       FIG. 273  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 12. This flowchart illustrates the processing operation of the receiver and the transmitter that outputs the light of the wavelengths illustrated in  FIG. 272 . 
     The transmitter expresses different signals by light (metameric light) perceived as isochromatic by humans but different in spectral distribution, and causes the light emitting unit to emit light (Step  7135   a ). The receiver measures the spectral distributions and receives the signals (Step  7135   b ). According to this method, the signal can be transmitted without concern for flicker. 
       FIG. 274  is a diagram illustrating an example of a structure of a system including the receiver and the transmitter in Embodiment 12. 
     The system includes an ID solution server  7038   a , a relay server  7038   b , a receiver  7038   c , a transmitter  7038   d , and a transmitter control device  7038   e.    
       FIG. 275  is a flowchart illustrating an example of processing operation of the system in Embodiment 12. 
     The ID solution server  7038   a  stores the ID of the transmitter  7038   d  and the method of communication between the transmitter control device  7038   e  and the receiver  7038   c , in association with each other (Step  7136   a ). The receiver  7038   c  receives the ID of the transmitter  7038   d , and obtains the method of communication with the transmitter control device  7038   e  from the ID solution server  7038   a  (Step  7136   b ). The receiver  7038   c  determines whether or not the receiver  7038   c  and the transmitter control device  7038   e  are directly communicable (Step  7136   c ). In the case where the determination result is false (N), the receiver  7038   c  communicates with the transmitter control device  7038   e  via the relay server  7038   b  (Step  7136   d ). In the case where the determination result is true (Y), the receiver  7038   c  communicates directly with the transmitter control device  7038   e  (Step  7136   e ). 
       FIG. 276  is a diagram illustrating an example of a structure of the system including the receiver and the transmitter in Embodiment 12. 
     The system includes a server  7039   g , a store device  7039   a , and a mobile device  7039   b . The store device  7039   a  includes a transmitter  7039   c  and an imaging unit  7039   d . The mobile device  7039   b  includes a receiver  7039   e  and a display unit  7039   f.    
       FIG. 277  is a flowchart illustrating an example of processing operation of the system in Embodiment 12. 
     The mobile device  7039   b  displays information on the display unit  7039   f  in 2D barcode or the like (Step  7137   a ). The store device  7039   a  captures the information displayed on the display unit  7039   f  by the imaging unit  7039   d , to obtain the information (Step  7137   b ). The store device  7039   a  transmits some kind of information from the transmitter  7039   c  (Step  7137   c ). 
     The mobile device  7039   b  receives the transmitted information by the receiver  7039   e  (Step  7137   d ). The mobile device  7039   b  changes the display on the display unit  7039   f , based on the received information (Step  7137   e ). The information displayed on the display unit  7039   f  may be determined by the mobile device  7039   b , or determined by the server  7039   g  based on the received information. 
     The store device  7039   a  captures the information displayed on the display unit  7039   f  by the imaging unit  7039   d , to obtain the information (Step  7137   f ). The store device  7039   a  determines the consistency between the obtained information and the transmitted information (Step  7137   g ). The determination may be made by the store device  7039   a  or by the server  7039   g . In the case where the obtained information and the transmitted information are consistent, the transaction is completed successfully (Step  7137   h ). 
     According to this method, coupon information displayed on the display unit  7039   f  can be protected from unauthorized copy and use. It is also possible to exchange an encryption key by this method. 
       FIG. 278  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. 
     The receiver starts the reception process (Step  7138   a ). The receiver sets the exposure time of the imaging device (Step  7138   b ). The receiver sets the gain of the imaging device (Step  7138   c ). The receiver receives information from the luminance of the captured image (Step  7138   d ). 
       FIG. 279  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. 
     The receiver sets the exposure time (Step  7139   a ). The receiver determines whether or not there is an API (Application Program Interface) that changes the exposure time (Step  7139   b ). In the case where the determination result is false (N), the imaging device is pointed to a high-luminance object such as a light source (Step  7139   c ). The receiver performs automatic exposure setting (Step  7139   d ). The receiver fixes the automatic exposure set value once the change of the automatic exposure set value has become sufficiently small (Step  7139   e ). 
     In the case where the determination result is true (Y), the receiver starts setting the exposure time using the API (Step  7139   f ). 
       FIG. 280  is a diagram illustrating an example of a structure of the system including the receiver and the transmitter in Embodiment 12. 
     The system includes a server  7036   a , a receiver  7036   b , and one or more transmitters  7036   c . The receiver  7036   b  obtains information relating to the one or more transmitters  7036   c  present near the receiver  7036   b , from the server. 
       FIG. 281  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. 
     The receiver  7036   b  performs self-position estimation from information of GPS, a base station, and the like (Step  7133   a ). The receiver  7036   b  transmits the estimated self-position and the estimation error range to the server  7036   a  (Step  7133   b ). The receiver  7036   b  obtains, from the server  7036   a , IDs of transmitters  7036   c  present near the position of the receiver  7036   b  and information associated with the IDs, and stores the IDs and the information (Step  7133   c ). The receiver  7036   b  receives an ID from a transmitter  7036   c  (Step  7133   d ). 
     The receiver  7036   b  determines whether or not information associated with the received ID is stored in the receiver  7036   b  (Step  7133   e ). In the case where the determination result is false (N), the receiver  7036   b  obtains the information from the server  7036   a , using the received ID as a key (Step  7133   f ). The receiver  7036   b  performs self-position estimation from the information received from the server  7036   a  and the position relation with the transmitter  7036   bc , obtains IDs of other nearby transmitters  7036   c  and information associated with the IDs from the server  7036   a , and stores the IDs and the information (Step  7133   g ). 
     In the case where the determination result is true (Y) in Step  7133   e  or after Step  7133   g , the receiver  7036   b  displays the information associated with the received ID (Step  7133   h ). 
       FIG. 282  is a diagram illustrating an example of application of the receiver and the transmitter in Embodiment 12. 
     Transmitters  7040   c  and  7040   d  such as lighting devices are disposed in a building a ( 7040   a ), and transmitters  7040   e  and  7040   f  such as lighting devices are disposed in a building b ( 7040   b ). The transmitters  7040   c  and  7040   e  transmit a signal A, and the transmitters  7040   d  and  7040   f  transmit a signal B. A receiver (terminal)  7040   g  such as a smartphone receives a signal transmitted from any of the transmitters. 
       FIG. 283  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. 
     The receiver  7040   g  detects the entry into a building (Step  7134   a ). The receiver  7040   g  transmits the estimated self-position, the estimation error range, and the name or the like of the building in which the receiver  7040   g  is estimated to be present, to the server (Step  7134   b ). The receiver  7040   g  obtains, from the server, IDs of transmitters present in the building in which the receiver  7040   g  is present and information associated with the IDs, and stores the IDs and the information (Step  7134   c ). The receiver  7040   g  receives an ID from a transmitter (Step  7134   d ). 
     The receiver  7040   g  determines whether or not information associated with the received ID is stored in the receiver  7040   g  (Step  7134   e ). In the case where the determination result is false (N), the receiver  7040   g  obtains the information from the server, using the received ID as a key (Step  7134   f ). The receiver  7040   g  obtains, from the server, IDs of other transmitters present in the same building as the transmitter from which the receiver  7040   g  receives the ID and information associated with the IDs, and stores the IDs and the information (Step  7134   g ). 
     In the case where the determination result is true (Y) in Step  7134   e  or after Step  7134   g , the receiver  7040   g  displays the information associated with the received ID (Step  7134   h ). 
       FIG. 284  is a diagram illustrating an example of a structure of the system including the receiver and the transmitter in Embodiment 12. 
     Transmitters  7041   a ,  7041   b ,  7041   c , and  7041   d  such as lighting devices transmit a signal A, a signal B, a signal C, and the signal B, respectively. A receiver (terminal)  7041   e  such as a smartphone receives a signal transmitted from any of the transmitters. Here, the transmitters  7041   a ,  7041   b , and  7041   c  are included in the error range of the self-position of the receiver  7041   e  estimated based on information of GPS, a base station, and the like (other means). 
       FIG. 285  is a flowchart illustrating an example of processing operation of the system in Embodiment 12. 
     The receiver  7041   e  receives an ID from a transmitter (Step  7140   a ). The receiver  7041   e  performs self-position estimation (Step  7140   b ). The receiver  7041   e  determines whether or not the self-position estimation is successful (Step  7140   c ). In the case where the determination result is false (N), the receiver  7041   e  displays a map or an input form, and prompts the user to input the current position (Step  7140   d ). 
     The receiver  7041   e  transmits the received ID, the estimated self-position, and the self-position estimation error range to the server (Step  7140   e ). 
     The server determines whether or not only one transmitter transmitting the ID received by the receiver  7041   e  is present within the estimation error range (estimation error radius) from the estimated self-position of the receiver  7041   e  (Step  7140   f ). In the case where the determination result is false (N), the receiver  7041   e  repeats the process from Step  7140   d . In the case where the determination result is true (Y), the server transmits information associated with the transmitter to the receiver  7041   e  (Step  7140   g ). 
       FIG. 286  is a flowchart illustrating an example of processing operation of the receiver in Embodiment 12. 
     The receiver detects a light emitting device (transmitter) emitting a signal (Step  7141   a ), and receives the signal (Step  7141   b ). The receiver displays the reception state, the received data amount, the transmission data amount, and the ratio of the received data amount to the transmission data amount (Step  7141   c ). 
     The receiver then determines whether or not the receiver has received all transmission data (Step  7141   d ). In the case of determining that the receiver has received all transmission data (Step  7141   d : Y), the receiver stops the reception process (Step  7141   e ), and displays the reception completion (Step  7141   f ). The receiver also outputs notification sound (Step  7141   g ), and vibrates ( 7141   h ). 
     In the case of determining that the receiver has not received all transmission data in Step  7141   d  (Step  7141   d : N), the receiver determines whether or not a predetermined time has elapsed from when the transmitter disappears from the frame of the imaging device (camera) of the receiver (Step  7141   i ). In the case of determining that the predetermined time has elapsed (Step  7141   i : Y), the receiver abandons the received data and stops the reception process (Step  7141   m ). The receiver also outputs notification sound (Step  7141   n ), and vibrates (Step  7141   p ). 
     In the case of determining that the predetermined time has not elapsed in Step  7141   i  (Step  7141   i : N), the receiver determines whether or not the sensor value of the 9-axis sensor of the receiver changes by a predetermined value or more, or whether or not the receiver is estimated to be pointed in another direction (Step  7141   j ). In the case of determining that the sensor value changes by the predetermined value or more or the receiver is estimated to be pointed in another direction (Step  7141   i : Y), the receiver performs the process from Step  7141   m  mentioned above. In the case of determining that the sensor value does not change by the predetermined value or more or the receiver is not estimated to be pointed in another direction (Step  7141   i : N), the receiver determines whether or not the sensor value of the 9-axis sensor of the receiver changes in a predetermined rhythm, or whether or not the receiver is estimated to be shaken (Step  7141   k ). In the case of determining that the sensor value changes in the predetermined rhythm or the receiver is estimated to be shaken, the receiver performs the process from Step  7141   m  mentioned above. In the case of determining that the sensor value does not change in the predetermined rhythm or the receiver is not estimated to be shaken (Step  7141   k : N), the receiver repeats the process from Step  7141   b.    
       FIG. 287A  is a diagram illustrating an example of a structure of the transmitter in Embodiment 12. 
     A transmitter  7046   a  includes a light emitting unit  7046   b , a 2D barcode  7046   c , and an NFC chip  7046   d . The light emitting unit  7046   b  transmits information common with at least one of the 2D barcode  7046   c  and the NFC chip  7046   d , by the method according to any of the above embodiments. Alternatively, the light emitting unit  7046   b  may transmit information different from at least one of the 2D barcode  7046   c  and the NFC chip  7046   d , by the method according to any of the above embodiments. In this case, the receiver may obtain the information common with at least one of the 2D barcode  7046   c  and the NFC chip  7046   d  from the server, using the information transmitted from the light emitting unit  7046   b  as a key. The receiver may perform a common process in the case of receiving information from the light emitting unit  7046   b  and in the case of receiving information from at least one of the 2D barcode  7046   c  and the NFC chip  7046   d . In either case, the receiver accesses a common server and displays common information. 
       FIG. 287B  is a diagram illustrating another example of a structure of the transmitter in Embodiment 12. 
     A transmitter  7046   e  includes a light emitting unit  7046   f , and causes the light emitting unit  7046   f  to display a 2D barcode  7046   g . That is, the light emitting unit  7046   f  has the functions of both the light emitting unit  7046   b  and the 2D barcode  7046   c  illustrated in  FIG. 287A . 
     Here, the light emitting unit  7046   b  or  7046   f  may transmit information indicating the size of the light emitting unit  7046   b  or  7046   f , to cause the receiver to estimate the distance from the receiver to the transmitter  7046   a  or  7046   e . This enables the receiver to capture the 2D barcode  7046   c  or  7046   g  more easily or clearly. 
       FIG. 288  is a flowchart illustrating an example of processing operation of the receiver and the transmitter  7046   a  or  7046   e  in Embodiment 12. Though the following describes, of the transmitters  7046   a  and  7046   e , the transmitter  7046   a  as an example, the processing operation of the transmitter  7046   e  is the same as that of the transmitter  7046   a.    
     The transmitter  7046   a  transmits information indicating the size of the light emitting unit  7046   b  (Step  7142   a ). Here, the maximum distance between arbitrary two points in the light emitting unit  7046   b  is set as the size of the light emitting unit  7046   b . Since speed is important in this series of processes, it is desirable that the transmitter  7046   a  directly transmits the information indicating the size of the light emitting unit  7046   b  of the transmitter  7046   a  and the receiver obtains the information Indicating the size without server communication. It is also desirable that the transmission is performed by a method that facilitates fast reception, such as the frequency of the brightness change of the transmitter  7046   a.    
     The receiver receives the signal which is the above-mentioned information, and obtains the size of the light emitting unit  7046   b  of the transmitter  7046   a  (Step  7142   b ). The receiver calculates the distance from the receiver to the light emitting unit  7046   b , based on the size of the light emitting unit  7046   b , the size of the captured image of the light emitting unit  7046   b , and the characteristics of the imaging unit (camera) of the receiver (Step  7142   c ). The receiver adjusts the focal length of the imaging unit to the calculated distance, and captures the image (Step  7142   d ). The receiver obtains the 2D barcode in the case of capturing the 2D barcode (Step  7142   e ). 
     Embodiment 13 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as an LED or organic EL blink pattern in Embodiments 1 to 12 described above. 
       FIG. 289  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 13. 
     In Step  7201   a , the transmitter outputs a sound of a specific frequency or a sound that changes in a specific pattern (the sound desirably has a frequency that is difficult to be heard by humans and collectable by a typical sound collector, e.g. 2 kHz to 20 kHz. A typical sound collector has a sampling frequency of about 44.1 kHz, and is only capable of precisely recognizing up to half of the frequency due to the sampling theorem. If the transmission signal is known, however, whether or not the signal is collected can be estimated with high accuracy. Based on this property, a signal of a frequency greater than or equal to 20 kHz may be used). 
     In Step  7201   b , the user presses a button on the receiver to switch from the power off state or the sleep state to the power on state. In Step  7201   c , the receiver activates a sound collecting unit. In Step  7201   d , the receiver collects the sound output from the transmitter. In Step  7201   e , the receiver notifies the user that the transmitter is present nearby, by screen display, sound output, or vibration. In Step  7201   f , the receiver starts reception, and then ends the process. 
       FIG. 290  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 13. 
     In Step  7202   a , the user presses a button on the receiver to switch from the power off state or the sleep state to the power on state. In Step  7202   b , the receiver activates an illuminance sensor. In Step  7202   c , the receiver recognizes a change of illuminance from the illuminance sensor. In Step  7202   d , the receiver receives a transmission signal from the illuminance sensor. In Step  7202   e , the receiver notifies the user that the transmitter is present nearby, by screen display, sound output, or vibration. In Step  7202   f , the receiver starts reception, and then ends the process. 
       FIG. 291  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 13. 
     In Step  7203   a , the user operates the receiver to start reception, or the receiver automatically starts reception by a trigger. In Step  7203   b , the reception is performed preferentially by an imaging unit whose average luminance of the entire screen is high or whose luminance at the maximum luminance point is high. The receiver then ends the process. 
       FIG. 292  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 13. 
     In Step  7204   a , the imaging unit captures, at high speed, the image of the simultaneous imaging lines or pixels in which the transmitter is shown, by not capturing the simultaneous imaging lines or pixels in which the transmitter is not shown. In Step  7204   b , the receiver detects the movement of the receiver or the hand movement using a gyroscope or a 9-axis sensor, makes adjustment by electronic correction so that the transmitter is always shown, and ends the process. 
       FIG. 293  is a flowchart illustrating an example of processing operation of the receiver and the transmitter in Embodiment 13. 
     In Step  7205   a , the receiver displays a 2D barcode A. In Step  7205   b , the transmitter reads the 2D barcode A. In Step  7205   c , the transmitter transmits a display change instruction. In Step  7205   d , the receiver displays a 2D barcode B. In Step  7205   e , the transmitter reads the 2D barcode B, and ends the process. 
       FIG. 294  is a diagram illustrating an example of application of the transmitter in Embodiment 13. 
     A transmitter  7211   a  has a mark  7211   b  indicating that the transmitter  7211   a  is a transmitter. Though humans cannot distinguish a transmission signal from ordinary light, they are able to recognize from the mark  7211   b  that the transmitter  7211   a  is a transmitter. Likewise, a transmitter  7211   c  has a mark  7211   d  indicating that the transmitter  7211   c  is a transmitter. A transmitter  7211   e  displays a mark  7211   f  indicating that the transmitter  7211   e  is a transmitter, only during signal transmission. 
       FIG. 295  is a diagram illustrating an example of application of the transmitter in Embodiment 13. 
     A transmitter  7212   a  such as a TV transmits a signal by changing the luminance of a backlight or a screen  7212   b . A transmitter  7212   c  such as a TV transmits a signal by changing the luminance of a part other than the screen, such as a bezel  7212   d  or a logo mark. 
       FIG. 296  is a diagram illustrating an example of application of the transmitter in Embodiment 13. 
     A transmitter  7213   a  such as a TV transmits a signal, when displaying a display  7213   c  such as urgent news, subtitles, or an on-screen display on a screen  7213   b . The display  7213   c  is displayed wide in the horizontal direction of the screen, with dark letters on a bright background. This eases the signal reception by the receiver. 
       FIG. 297  is a diagram illustrating an example of application of the transmitter and the receiver in Embodiment 13. 
     When the user operates a remote control  7214   a  of a receiver or a TV, the remote control  7214   a  transmits a start signal to a transmitter  7214   b . The transmitter  7214   b  transmits a signal for a predetermined time after receiving the start signal. The transmitter  7214   b  displays a display  7214   c  indicating that the signal is being transmitted. This eases the signal reception by the receiver, even in the case where the display of the TV itself is dark. The receiver can receive the signal more easily when the display  7214   c  has more bright portions and is wide in the horizontal direction. 
     The transmitter  7214   b  may have the area  7214   c  for signal transmission, apart from the area for displaying TV images. The transmitter  7214   b  may recognize the movement of the user or the movement of the remote control  7214   a  by a camera  7214   d  or a microphone  7214   e , and start signal transmission. 
       FIG. 298  is a diagram illustrating an example of application of the transmitter and the receiver in Embodiment 13. 
     Transmitters  7215   a  and  7215   b  each transmit the ID number of the transmitter. The ID of the transmitter may be an ID that is completely unique, or an ID that is unique within a region, a building, or a room. In the latter case, it is desirable that the same ID is not present within several tens of meters. A receiver  7215   c  transmits the received ID to a server  7215   d . The receiver  7215   c  may also transmit the position information of the receiver  7215   c  recognized by a position sensor such as GPS, the terminal ID of the receiver  7215   c , a user ID, a session ID, and the like to the server. 
     A database  7215   e  stores, in association with the ID transmitted from the transmitter, another ID, the position information (latitude, longitude, altitude, room number) of the transmitter, the model, shape, or size of the transmitter, content such as text, image, video, and music, an instruction or program executed by the receiver, a URL of another server, information of the owner of the transmitter, the registration date or expiration date of the ID, and so on. 
     The server  7215   d  reads the information associated with the received ID from the database, and transmits the information to the receiver  7215   c . The receiver  7215   c  performs a process such as displaying the received information, accessing another server based on the received information, or executing the received instruction. 
       FIG. 299  is a diagram illustrating an example of application of the transmitter and the receiver in Embodiment 13. 
     As in the case of  FIG. 298 , transmitters  7216   a  and  7216   b  each transmit an ID 1 of the transmitter. A receiver  7216   c  transmits the received ID 1 to a server A  7216   d . The server A transmits an ID 2 and information (URL, password, etc.) for accessing another server B, which are associated with the ID 1. The receiver  7216   c  transmits the ID 2 to the server B  7216   f . The server B  7216   f  transmits information associated with the ID 2 to the receiver  7216   c , and performs a process associated with the ID 2. 
       FIG. 300  is a diagram illustrating an example of application of the transmitter and the receiver in Embodiment 13. 
     As in the case of  FIG. 298 , transmitters  7217   a  and  7217   b  each transmit an ID 1 of the transmitter. A receiver  7217   c  transmits the received ID 1 to a server A  7217   d . The server A transmits information associated with the ID 1 and randomly generated key information to a server B. The key information may be generated by the server B and transmitted to the server A. The server A transmits the key information and information (URL, password, etc.) for accessing the server B, to the receiver. The receiver  7217   c  transmits the key information to the server B  7217   f . The server B  7217   f  transmits information associated with the ID 2 to the receiver  7217   c , or performs a process associated with the ID 2. 
       FIG. 301A  is a diagram illustrating an example of the transmission signal in Embodiment 13. 
     The signal is made up of a header unit  7218   a , a data unit  7218   b , a padding unit  7218   c , and an End of Data unit  7218   e . The signal repeatedly carries the same data for 1/15 second. Hence, even in the case where the receiver receives only part of the signal, the receiver can decode the signal. The receiver extracts the header unit from the received signal, and decodes the data by treating the part between two header units as the data unit. A shorter data unit per frame enables decoding even in the case where the transmitter is shown in a small size in the imaging unit of the receiver. A longer data unit per frame, on the other hand, contributes to faster communication. By repeating the same data for 1/15 second, a receiver that captures 30 frames per second can reliably capture the signal of the data unit even when there is blanking. In addition, the same signal is received in either one of adjacent frames, with it being possible to confirm the reception result. The signal can be received even in the case where nonconsecutive frames are not processed due to the operation of another application or the receiver is only capable of capturing 15 frames per second. Since data nearer the header unit can be received more easily, important data may be located near the header unit. 
       FIG. 301B  is a diagram illustrating another example of the transmission signal in Embodiment 13. 
     As in the example in  FIG. 301A , the signal is made up of the header unit  7218   a , the data unit  7218   b , the padding unit  7218   c , and the End of Data unit  7218   e . The signal repeatedly carries the same data for 1/30 second. Hence, even in the case where the receiver receives only part of the signal, the receiver can decode the signal. A shorter data unit enables decoding even in the case where the transmitter is shown in a small size in the imaging unit of the receiver. A longer data unit, on the other hand, contributes to faster communication. By repeating the same data for 1/30 second, a receiver that captures 30 frames per second can reliably capture the signal of the data unit even when there is blanking. In addition, the same signal is received in either one of adjacent frames, with it being possible to confirm the reception result. Since data nearer the header unit can be received more easily, important data may be located near the header unit. 
       FIG. 302  is a diagram illustrating an example of the transmission signal in Embodiment 13. 
     A modulation scheme  7219   a  for modulating a 2-bit signal to a 5-bit signal, though lower in modulation efficiency than a modulation scheme such as  2200 . 2   a  for modulating a 2-bit signal to a 4-bit signal, can express a header pattern in the same form as data, and therefore suppress flicker as compared with inserting a header pattern of a different form. End of Data may be expressed using a header in the data unit. 
       FIG. 303A  is a diagram illustrating an example of the transmission signal in Embodiment 13. 
     The signal is made up of a data unit  7220   a , a buffer unit  7220   b , and an End of Data unit  7220   d . The buffer unit may be omitted. The signal repeatedly carries the same data for 1/15 second. A header such as the header  7218   a  is unnecessary in the case of using, for example, FM modulation of transmitting a signal by a light emission frequency. 
       FIG. 303B  is a diagram illustrating another example of the transmission signal in Embodiment 13. 
     As in the example in  FIG. 303A , the signal is made up of the data unit  7220   a , the buffer unit  7220   b , and the End of Data unit  7220   d . The buffer unit may be omitted. The signal repeatedly carries the same data for 1/30 second. A header such as the header  7218   a  is unnecessary in the case of using, for example, FM modulation of transmitting a signal by a light emission frequency. 
       FIG. 304  is a diagram illustrating an example of the transmission signal in Embodiment 13. 
     Signals are assigned according to frequency. Since the receiver detects frequencies from signal periods, reception errors can be reduced by assigning signals so that the inverses or logarithms of frequencies are at regular intervals, rather than by assigning frequencies to signals at regular intervals. In the case where the imaging unit of the receiver captures light for transmitting data  1  and data  2  within one frame, Fourier transforming the luminance in the direction perpendicular to the exposure lines results in the occurrence of weaker peaks in the frequencies of the data  1  and the data  2  than in the case where light for transmitting single data is captured. 
     According to this method, the transmission frequency can be analyzed even in the case where light transmitted at a plurality of frequencies in sequence is captured in one frame, and the transmission signal can be received even when the frequency of the transmission signal is changed at time intervals shorter than 1/15 second or 1/30 second. 
     The transmission signal sequence can be recognized by performing Fourier transform in a range shorter than one frame. Alternatively, captured frames may be concatenated to perform Fourier transform in a range longer than one frame. In this case, the luminance in the blanking time in imaging is treated as unknown. 
       FIGS. 305A and 305B  are diagrams illustrating an example of the transmission signal in Embodiment 13. 
     In the case where the frequency of the transmission signal is less than or equal to 200 Hz, the light appears to blink to humans. In the case where the frequency exceeds 200 Hz, the light appears to be continuous to humans. A camera captures blinking light in frequencies up to about 500 Hz (1 kHz depending on conditions). It is therefore desirable that the signal frequency (carrier frequency) is greater than or equal to 1 kHz. The signal frequency may be greater than or equal to 200 Hz if there is little effect of the camera capturing flicker. Harmonic noise of a lighting device increases in frequencies greater than or equal to 20 kHz. This can be avoided by setting the signal frequency to less than or equal to 20 kHz. Besides, since sound due to coil oscillation occurs in a range from 500 Hz to 3 kHz, it is necessary to set the signal frequency to greater than or equal to 3 kHz or fix the coil. When the signal frequency is 1 kHz (period of 1 millisecond), the exposure time of the imaging device needs to be set to less than or equal to half, i.e. 0.5 millisecond (= 1/2000 second), in order to recognize the signal asynchronously. In the case of employing frequency modulation in the signal modulation scheme, too, the exposure time of the imaging device needs to be set to less than or equal to half the signal period, due to the sampling theorem. In the case of the modulation scheme that expresses the value by the frequency itself as in  FIG. 304 , on the other hand, the exposure time of the imaging device can be set to less than or equal to about 4 times the signal period, because the frequency can be estimated from signal values at a plurality of points. 
       FIG. 306  is a diagram illustrating an example of application of the transmitter in Embodiment 13. 
     A transmitter  7223   a  such as a lighting transmits an ID. A receiver  7223   b  such as a personal computer receives the ID, and transmits the ID and a file  7223   e  to a server  7223   d . The server  7223   d  stores the file  7223   e  and the ID in association with each other, and permits a personal computer transmitting the same ID to access the file. Here, a plurality of access controls, such as read-only permission and read and write permission, may be applied according to the ID. A receiver  7223   c  such as a personal computer receives the ID, transmits the ID to the server  7223   d , and accesses the file  7223   e  on the server. The server  7223   d  deletes the file or initializes access control, in the case where a predetermined time has elapsed from when the file is accessed last time or in the case where the personal computer  7223   b  transmits a different ID. The personal computer  7223   b  or the personal computer  7223   c  may transmit an ID. 
       FIG. 307  is a diagram illustrating an example of application of the transmitter in Embodiment 13. 
     A transmitter  7224   b  registers its ID information in a server  7224   d . A receiver  7224   a  displays a coupon, an admission ticket, member information, or prepaid information on the screen. The transmitter  7224   b  transmits the ID. The receiver  7224   a  receives the ID, and transmits the received ID, a user ID, a terminal ID, and the information displayed on the screen to the server  7224   d . The server  7224   d  determines whether or not the information displayed on the receiver  7224   a  is valid, and transmits the result to a display device  7224   c . The server  7224   d  may transmit key information that changes with time to the transmitter  7224   b , which then transmits the key information. Here, the server  7224   d  may be implemented as the same device as the transmitter  7224   b  or the display device  7224   c . In a system of displaying a coupon, an admission ticket, member information, or prepaid information on the screen of the receiver  7224   a  in 2D barcode or the like and reading the displayed information, the information can be easily falsified by displaying an image obtained by copying the screen. According to this method, however, it is possible to prevent the falsification of the screen by copying. 
       FIGS. 308 to 310  are diagrams for describing the imaging element in Embodiment 13. 
       FIG. 308  is a front view of an imaging element  800  according to the present disclosure. As described with the drawings in the foregoing embodiments, to improve the optical communication speed according to the present disclosure, only the data of scan lines, e.g. n=4 to 7, of an area  830   a  in a light signal generation unit  830  is obtained by repetitive scan by supplying a scan line selection signal to vertical access means  802 , while tracking the light signal generation unit  830  as illustrated in  FIG. 310 . As a result, continuous light signals according to the present disclosure can be extracted as illustrated in the lower part of  FIG. 310 . In detail, continuous signals such as 4, 5, 6, 7 followed by the blanking time and 4, 5, 6, 7 followed by the blanking time can be obtained. The blanking can be limited to 2 μs or less in the current imaging element process. When the blanking is limited to 2 μs or less, the data can be demodulated substantially continuously because, in the case of 30 fps, one frame is 33 ms and, in the case of 1000 lines, one line is 33 μs. 
     In the present disclosure, in the imaging element (image sensor) in a rolling shutter mode, first the shutter speed is increased to display the lines according to the present disclosure, and then the signal is obtained. After this, the image  830  of the light source moves up, down, left, or right due to hand movement of the user of the camera. This causes the image  830  to be partially outside the lines n=4 to 7, as a result of which the signal is interrupted and an error occurs. In view of this, hand movement detection and correction means  832  is used for correction, to fix the image  830 . Alternatively or in combination with this, means  834  of detecting the line number of the position of the image  830  is used to specify the line number n of the image  830 , and a line selection unit  835  controls the vertical access means to change the line number to a desired line n (e.g. n=7 to 10). As a result, the image  830  is obtained and so the continuous signals are obtained. Thus, data with few errors can be received at high speed. 
     Referring back to  FIG. 308 , the imaging element  800  is further described below. There are horizontal pixels a to k, which are accessible by horizontal access means  801 . Meanwhile, there are 12 vertical pixels where n=1 to 12.  803   a  to  803   n  are read for each column to a line memory  805  and output from an output unit  808 . 
     As illustrated in  FIG. 309 , in the present disclosure, first the data is sequentially read in a normal imaging mode as in (a). A blanking time  821  is provided between normal frames, during which various adjustment operations for video signals, such as color, are conducted. 
     The signal cannot be obtained in a time period of 5% to 20%, though this differs depending on the imaging element. Since the reception pattern specific to the present disclosure is unable to be obtained, when the imaging device enters a data signal reception mode in Step  820   c , first the shutter speed is increased to increase the gain, thus receiving the data. In the case of Yes, the blanking time  821  is reduced to a blanking time  821   a  by stopping part of the above-mentioned video imaging operations for color, brightness, sensitivity, and so on. As a result of such a reduction by omitting adjustment operations, the blanking time  821   a  can be limited to 2 μs or less in the current process. This delivers a significant reduction in burst error of the input signal, and so enables much faster transmission. 
     In the case where only a partial image is captured as the image  830  as in  FIG. 310 , the information of the lines other than n=4 to 8 is not obtained. This causes a large burst error, leading to lower reception efficiency and a significant decrease in transmission amount. 
     The image position detection means  834  in  FIG. 310  detects the position and size of the image  830 . In the case where the image is small, the imaging element is switched to a high-speed read mode in Step  820   d , and scans only the lines (n=4 to 7) in which the image  830  is captured. Line signals  803   d ,  803   e ,  803   f , and  803   g  are repeatedly read as in (c), as a result of which the pattern specific to the present disclosure is read seamlessly. Continuous data reception with almost no burst error can thus be performed at a significantly improved data rate. 
     In detail, a transmission rate of about 2400 bps is achieved when the carrier is 4.8 kHz in the current imaging element. A transmission rate of several tens of kbps is expected with faster imaging elements in the future. 
     After the data read is completed in Step  820   e , the shutter speed is decreased to increase the blanking time, and the imaging element returns to the normal imaging mode in (a). 
     The above-mentioned blanking time reduction and repetitive reading of specific lines ensures that synchronous signals or addresses are read, and enables much faster transmission in the pattern transmission method according to the present disclosure. 
     (Variations) 
     The following describes variations or supplements to each of the above embodiments. 
       FIG. 311A  is a flowchart illustrating processing operation of the reception device (imaging device).  FIG. 311A  illustrates more detailed processing operation than that in  FIG. 71 . 
     Here, the imaging unit of the receiver employs not a mode (global shutter mode) of simultaneously exposing all light receiving elements but a mode (rolling shutter mode, focal plane shutter mode) of sequentially exposing the light receiving elements one by one with a time difference. The term “exposure” used in the description of the present disclosure includes an exposure mode of controlling the time during which an imaging element is exposed to light by a physical shutter, and an exposure mode of extracting only the output of an imaging element during a specific time by an electronic shutter. 
     First, in Step  7340   a , in the case where the imaging mode is the global shutter mode, the receiver changes the imaging mode to the rolling shutter mode. Next, in Step  7340   b , the receiver sets the shutter speed so that a bright line is captured when capturing a subject whose moving average luminance with a time width greater than or equal to 5 milliseconds is unchanged and that changes in luminance in a region less than or equal to 5 milliseconds. 
     In Step  7340   c , the receiver sets the sensitivity of the light receiving element to increase the difference between the bright part and the dark part of the bright line. In Step  7340   d , the receiver sets the imaging mode to a macro imaging mode, or sets a shorter focal length than focusing on the transmitter. Capturing the transmitter in a larger size in a blurred state enables an increase in the number of exposure lines in which the bright line is captured. 
     In Step  7340   e , the receiver observes the change in luminance of the bright line in the direction perpendicular to the exposure line. In Step  7340   f , the receiver calculates the interval between the parts of rapid rise in luminance or the interval between the parts of rapid fall in luminance and reads the transmission signal from the interval, or calculates the period of luminance change and reads the transmission signal from the period. 
       FIG. 311B  is a diagram illustrating an image obtained in the normal imaging mode and an image obtained in the macro imaging mode in comparison. As illustrated in  FIG. 311B , an image  7307   b  obtained by capturing the light emitting subject in the macro imaging mode includes a larger bright area than an image  7307   a  obtained by capturing the same subject in the normal imaging mode. Thus, the bright line can be generated in more exposure lines for the subject in the macro imaging mode. 
       FIG. 312  is a diagram illustrating a display device that displays video and the like. 
     A display device  7300   a  including a liquid display or the like displays video in a video area  7300   b , and various information in an information display area  7300   c . The display device  7300   a  is configured as a transmitter (transmission device), and transmits a signal by changing the luminance of the backlight. 
       FIG. 313  is a diagram illustrating an example of processing operation of the display device  7300   a.    
     First, in Step  7350   a , the display device  7300   a  enters the signal transmission mode. Next, in Step  7350   b , the display device  7300   a  transmits the signal by changing the luminance of the backlight in the information display area  7300   c.    
       FIG. 314  is a diagram illustrating an example of the signal transmission part in the display device  7300   a.    
     The display device  7300   a  transmits the signal by changing the luminance of each part ( 7301   d ,  7301   f ,  7301   g ,  7301   i ) where the backlight is ON, and transmits no signal from the other parts ( 7301   c ,  7301   e ,  7301   h ,  7301   j ). 
       FIG. 315  is a diagram illustrating another example of processing operation of the display device  7300   a.    
     First, in Step  7351   a , the display device  7300   a  enters the signal transmission mode. Next, in Step  7351   b , the display device  7300   a  transmits the signal only from the part where the backlight is ON, in the case where the backlight is turned OFF upon screen change for improved dynamic resolution. In Step  7351   c , the display device  7300   a  transmits no signal when the backlight is OFF in the entire screen. 
       FIG. 316  is a diagram illustrating another example of the signal transmission part in the display device  7300   a.    
     The display device  7300   a  turns OFF the backlight control for improved dynamic resolution in each part ( 7302   b ,  7302   e ,  7302   g ,  7302   j ), and transmits the signal from these parts. Meanwhile, the display device  7300   a  turns ON the backlight control for improved dynamic resolution in the other parts ( 7302   c ,  7302   d ,  7302   h ,  7301   i ). 
       FIG. 317  is a diagram illustrating yes another example of processing operation of the display device  7300   a.    
     First, in Step  7352   a , the display device  7300   a  enters the signal transmission mode. Next, in Step  7352   b , the display device  7300   a  turns OFF the backlight control for improved dynamic resolution in the part ( 7302   b ,  7302   e ,  7302   g ,  7202   j ) of the screen, and transmits the signal from the part. 
     In Step  7352   c , the display device  7300   a  adjusts the average luminance of the backlight so that the brightness of the part transmitting the signal is equal to the average luminance of the backlight in the part transmitting no signal. This adjustment may be made by adjusting the time ratio of blinking of the backlight during signal transmission or by adjusting the maximum luminance of the backlight. 
       FIG. 318  is a diagram illustrating a structure of a communication system including the transmitter and the receiver. 
     The communication system includes transmitters  7303   a  and  7303   b , a control device  7303   c , a network  7303   d , an ID management server  7303   e , a wireless access point  7303   f , and receivers  7303   g  and  7303   h.    
       FIG. 319  is a flowchart illustrating processing operation of the communication system in  FIG. 318 . 
     First, in Step  7353   a , the ID of the transmitter, the information (SSID, password, ID of wireless access point, radio frequency, position information of access point, connectable position information, etc.) of the wireless access point  7303   f , and the information (IP address, etc.) of the control device  7303   c  are stored in the ID management server  7303   e  in association with each other. Next, in Step  7353   b , the transmitter  7303   a  or  7303   b  transmits the ID of the transmitter  7303   a  or  7303   b . The transmitter  7303   a  or  7303   b  may also transmit the information of the wireless access point  7303   f  and the information of the control device  7303   c . In Step  7353   c , the receiver  7303   g  or  7303   h  receives the ID of the transmitter  7303   a  or  7303   b  and obtains the information of the wireless access point  7303   f  and the information of the control device  7303   c  from the ID management server  7303   e , or receives the ID of the transmitter  7303   a  or  7303   b  and the information of the wireless access point  7303   f.    
     In Step  7353   d , the transmitter  7303   a  or  7303   b  connects to the wireless access point  7303   f . In Step  7353   e , the transmitter  7303   a  or  7303   b  transmits the address of the ID management server  7303   e  on the network, an instruction to the ID management server  7303   e , and the ID of the transmitter  7303   a  or  7303   b  to the control device  7303   c.    
     In Step  7353   f , the control device  7303   c  transmits the received ID to the receiver  7303   g  or  7303   h . In Step  7353   g , the control device  7303   c  issues the instruction to the ID management server  7303   e  on the network, and obtains a response. Here, the control device  7303   c  operates as a proxy server. 
     In Step  7353   h , the control device  7303   c  transmits the response and the received ID, from the transmitter  7303   a  or  7303   b  indicated by the transmitter ID. The transmission may be repeatedly performed until the reception completion is notified from the receiver  7303   g  or  7303   h  or a predetermined time elapses. 
     In Step  7353   i , the receiver  7303   g  or  7303   h  receives the response. In Step  7353   j , the receiver  7303   g  or  7303   h  transmits the received ID to the control device  7303   c , and notifies the reception completion. 
     In Step  7353   k , in the case where the receiver  7303   g  or  7303   h  is at a position where the signal from the transmitter  7303   a  or  7303   b  cannot be received, the receiver  7303   g  or  7303   h  may notify the control device  7303   c  to return the response via the wireless access point  7303   f.    
       FIG. 320  is a diagram illustrating a variation of signal transmission in each of the above embodiments. 
     In the reception method according to the present disclosure, the signal transmission efficiency is higher when the light emitting unit of the transmitter is captured in a larger size in the imaging unit of the receiver. That is, the signal transmission efficiency is low in the case where a small electric bulb or a high ceiling lighting is used as the light emitting unit of the transmitter. The signal transmission efficiency can be enhanced by applying light of a transmitter  7313   a  to a wall, a ceiling, a floor, a lamp shade, or the like and capturing reflected light  7313   b  by a receiver  7313   c.    
       FIG. 321  is a diagram illustrating a variation of signal transmission in each of the above embodiments. 
     Signal transmission is performed by a transmitter  7314   d  projecting light including a transmission signal onto an exhibit  7314   a  and a receiver  7314   c  capturing reflected light  7314   b.    
       FIG. 322  is a diagram illustrating a variation of signal transmission in each of the above embodiments. 
     A signal transmitted from a transmitter  7315   a  is received by a receiver  7315   b  including an illuminance sensor. The receiver  7315   b  receives the signal not by an imaging element but by an illuminance sensor. Such a receiver is low in power consumption, suitable for constant signal reception, lightweight, and manufacturable at low cost. 
     The receiver  7315   b  is formed as a part of glasses, an earring, a hair accessory, a wristwatch, a hearing aid, a necklace, a cane, a trolley, or a shopping cart. The receiver  7315   b  performs video display, audio reproduction, or vibration, according to the received signal. The receiver  7315   b  also transmits the received signal to a mobile information terminal  7315   c  via a wireless or wired transmission path. 
       FIG. 323A  is a diagram illustrating a variation of signal transmission in each of the above embodiments. 
     A projector  7316   a  transmits a signal, using projection light as the transmission signal. A receiver  7316   c  captures reflected light from a screen  7316   b , to receive the signal. The receiver  7316   c  displays content and its ancillary information projected by the projector  7316   a , on a screen  7316   d . The content displayed on the screen  7316   d  may be transmitted as the transmission signal, or obtained from a server  7316   e  based on an ID included in the transmission signal. 
       FIG. 323B  is a diagram illustrating a variation of signal transmission in each of the above embodiments. 
     A receiver  7317   b  receives a signal transmitted from a transmitter  7317   a . The receiver  7317   b  transmits audio to an earphone or hearing aid  7317   c  registered in the receiver  7317   b . In the case where visual impairment is included in a user profile registered in the receiver  7317   b , the receiver  7317   b  transmits audio commentary for the visually impaired to the earphone  7317   c.    
       FIG. 323C  is a diagram illustrating a variation of signal transmission in each of the above embodiments. 
     A receiver  7318   c  receives a signal transmitted from a transmitter  7318   a  or  7318   b . The receiver  7318   c  may receive the signal using an illuminance sensor. The inclusion of an illuminance sensor with high directivity enables the receiver  7318   c  to accurately estimate the direction to the transmitter. Moreover, the inclusion of a plurality of illuminance sensors enables the receiver  7318   c  to receive the transmission signal in a wider range. The receiver  7318   c  transmits the received signal to an earphone  7318   d  or a head-mounted display  7318   e.    
       FIG. 323D  is a flowchart illustrating processing operation of a communication system including the receiver and the display or the projector. This flowchart illustrates processing operation corresponding to any of the examples of signal transmission illustrated in  FIGS. 323A to 323C . 
     First, in Step  7357   a , the ID of the transmitter, the display content ID, and the content displayed on the display or the projector are stored in the ID management server in association with each other. Next, in Step  7357   b , the transmitter displays the content on the display or the projector, and transmits the signal using the backlight of the display or the projection light of the projector. The transmission signal may include the ID of the transmitter, the display content ID, the URL in which the display content is stored, and the display content itself. 
     In Step  7357   c , the receiver receives the transmission signal. In Step  7357   d , the receiver obtains the content displayed on the display or the projector by the transmitter, based on the received signal. 
     In Step  7357   e , in the case where a user profile is set in the receiver, the receiver obtains content suitable for the profile. For example, the receiver obtains subtitle data or audio content for at hand reproduction in the case where a profile of hearing impairment is set, and obtains content for audio commentary in the case where a profile of visual impairment is set. 
     In Step  7357   f , the receiver displays the obtained image content on the display of the receiver, and reproduces the obtained audio content from the speaker of the receiver, the earphone, or the hearing aid. 
       FIG. 324  is a diagram illustrating an example of the transmission signal in Embodiment 12.  FIG. 324  illustrates the transmission signal in  FIG. 250  in detail. 
     In the case of coding the transmission signal by the method in any of  FIGS. 27 to 87, 302 , and the like, the receiver can decode the transmission signal by detecting points  7308   c ,  7308   d , and  7308   e  at which the luminance rises rapidly. In this case, transmission signals  7308   a  and  7308   b  are equivalent and represent the same signal. 
     Accordingly, the average luminance can be changed by adjusting the time of luminance fall, as in the transmission signals  7308   a  and  7308   b . When there is a need to change the luminance of the transmitter, by adjusting the average luminance in this way, the luminance can be adjusted without changing the transmission signal itself. 
       FIG. 325  is a diagram illustrating an example of the transmission signal in Embodiment 3.  FIG. 325  illustrates the transmission signal in  FIG. 34  in detail. 
     Transmission signals  7309   a  and  7309   b  can be regarded as equivalent to a transmission signal  7309   c , when taking the average luminance of a length such as  7309   d . Another signal can be superimposed by changing the luminance with a time width unobservable by other receivers, as in the transmission signals  7309   a  and  7309   b.    
       FIG. 326  is a diagram illustrating another example of the transmission signal in Embodiment 3.  FIG. 326  illustrates the transmission signal in  FIG. 34  in detail. 
     Another signal is superimposed by adding a luminance change with a time width unobservable by other receivers to a transmission signal  7310   a , as in  7310   c . In the case where the signal cannot be superimposed in a luminance fall section in the transmission signal  7310   a , a high-speed modulation signal can be transmitted intermittently by adding a start signal and an end signal to a high-speed modulation part as in  7310   e.    
       FIG. 327A  is a diagram illustrating an example of the imaging element of the receiver in each of the above embodiments. 
     Many imaging elements have a layout  7311   a , and so cannot capture the transmitter while capturing the optical black. A layout  7311   b , on the other hand, enables the imaging element to capture the transmitter for a longer time. 
       FIG. 327B  is a diagram illustrating an example of a structure of an internal circuit of the imaging device of the receiver in each of the above embodiments. 
     An imaging device  7319   a  includes a shutter mode change unit  7319   b  that switches between the global shutter mode and the rolling shutter mode. Upon reception start, the receiver changes the shutter mode to the rolling shutter mode. Upon reception end, the receiver changes the shutter mode to the global shutter mode, or returns the shutter mode to a mode before reception start. 
       FIG. 327C  is a diagram illustrating an example of the transmission signal in each of the above embodiments. 
     In the case where the carrier is set to 1 kHz as a frequency at which no flicker is captured by a camera, one slot is 1 millisecond ( 7320   a ). In the modulation scheme (4-value PPM modulation) in  FIG. 28 , the average of one symbol (4 slots) is 75% ( 7320   b ), and the range of the moving average for 4 milliseconds is 75%±(modulation factor)/4. Flicker is smaller when the modulation factor is lower. Assuming one symbol as one period, the carrier is greater than or equal to 800 Hz in the case where the frequency at which no flicker is perceived by humans is greater than or equal to 200 Hz, and the carrier is greater than or equal to 4 kHz in the case where the frequency at which no flicker is captured by a camera is greater than or equal to 1 kHz. 
     Likewise, in the case where the carrier is set to 1 kHz, in the modulation scheme (5-value PPM modulation) in  FIG. 302 , the average of one symbol (5 slots) is 80% ( 7320   c ), and the range of the moving average for 5 milliseconds is 80%±(modulation factor)/5. Flicker is smaller when the modulation factor is lower. Assuming one symbol as one period, the carrier is greater than or equal to 1 kHz in the case where the frequency at which no flicker is perceived by humans is greater than or equal to 200 Hz, and the carrier is greater than or equal to 5 kHz in the case where the frequency at which no flicker is captured by a camera is greater than or equal to 1 kHz. 
       FIG. 327D  is a diagram illustrating an example of the transmission signal in each of the above embodiments. 
     A header pattern is different from a pattern representing data, and also needs to be equal in average luminance to the pattern representing data, in order to eliminate flicker. Patterns such as  7321   b ,  7321   c ,  7321   d , and  7321   e  are available as patterns equal in average luminance to the data pattern in the modulation scheme of  2200 . 2   a . The pattern  7321   b  is desirable in the case where the luminance value can be controlled in levels. In the case where the luminance change is sufficiently faster than the exposure time of the imaging device in the receiver as in the pattern  7321   e , the signal is observed as in  7321   b  by the receiver. The modulation scheme  7219   a  is defined in the form that includes the header pattern. 
       FIG. 328A  is a diagram for describing an imaging mode of the receiver. 
     In the normal imaging mode, the receiver obtains an image  7304   a  by performing imaging using all exposure lines (imaging lines) included in the image sensor. As an example, the total number of exposure lines is 3000. Through such imaging, the receiver obtains one image from time t 1  to time t 4 , and further obtains one image from time t 5  to time t 8 . 
     In the case where the subject which is the transmitter is shown in only one part of the image, there is a possibility that the receiver cannot receive the signal from the subject. Suppose only the exposure lines  1001  to  2000  capture the subject and the other exposure lines do not capture the subject. When the exposure lines  1001  to  2000  are not exposed, that is, when the exposure lines  1  to  1000  are exposed (time t 1  to time t 2 , time t 5  to time t 6 ) and when the exposure lines  2001  to  3000  are exposed (time t 3  to time t 4 , time t 7  to time t 8 ), the receiver cannot receive the signal from the subject. 
     When the imaging mode is switched from the normal imaging mode to a special imaging mode A, the receiver uses, for imaging, only the exposure lines capturing the subject from among all exposure lines. That is, the receiver uses only the exposure lines  1001  to  2000  for imaging, from time t 1  to time t 4  and from time t 5  to time t 8 . In the special imaging mode A, the exposure lines  1001  to  2000  are uniformly exposed in sequence only once throughout the imaging time of one frame, e.g. from time t 1  to time t 4  or from time t 5  to time t 8 . The receiver can thus be prevented from missing the reception of the signal from the subject. 
       FIG. 328B  is a flowchart illustrating processing operation of the receiver using the special imaging mode A. 
     First, in Step  7354   a , the receiver detects the part in which the bright line is captured, from the captured image. Next, in Step  7354   b , the receiver sets the hand movement correction function to ON. 
     In Step  7354   c , the receiver switches to the special imaging mode A in which the imaging is performed using only the pixels of the exposure lines in which the bright line is captured. In the special imaging mode A, the exposure time of each exposure line is set so that the time from when the exposure of one exposure line starts to when the exposure of the next exposure line starts is uniform during the imaging time of one image (e.g. from time t 1  to time t 4 ). Here, one or more pixels in the direction perpendicular to the exposure lines may be omitted in the imaging. 
     Since the number of frames output from the imaging unit of the receiver is the same as that in the normal imaging mode, the special imaging mode A is suitable for a receiver that includes a low-performance processor or a receiver that includes a processor also engaged in other processes. 
     In Step  7354   d , the receiver designates the area of imaging in the special imaging mode A. By designating a narrower area than the area in which the bright line is captured as the area of imaging, it is possible to keep capturing the bright line even when the imaging direction changes due to hand movement and the like. 
     In Step  7354   e , the receiver detects the movement of the captured image. By moving the area of imaging in the moving direction, it is possible to keep capturing the bright line even when the position of the captured image changes. In Step  7354   f , the receiver obtains the transmitted information from the pattern of the bright line. 
       FIG. 329A  is a diagram for describing another imaging mode of the receiver. 
     When the imaging mode is switched from the normal imaging mode to a special imaging mode B, the receiver uses, for imaging, only the exposure lines capturing the subject from among all exposure lines. That is, the receiver uses only the exposure lines  1001  to  2000  for imaging, from time t 1  to time t 4  and from time t 5  to time t 8 . In the special imaging mode B, the exposure lines  1001  to  2000  are exposed in sequence a plurality of times throughout the imaging time of one frame, e.g. from time t 1  to time t 4  or from time t 5  to time t 8 . The receiver can thus be prevented from missing the reception of the signal from the subject. 
       FIG. 329B  is a flowchart illustrating processing operation of the receiver using the special imaging mode B. 
     First, in Step  7355   a , the receiver detects the part in which the bright line is captured, from the captured image. Next, in Step  7355   b , the receiver sets the hand movement correction function to ON. 
     In Step  7355   c , the receiver switches to the special imaging mode B in which the imaging is performed using only the pixels of the exposure lines in which the bright line is captured. In the special imaging mode B, the imaging is performed at high speed by subjecting only the area in which the bright line is captured to the imaging. Here, one or more pixels in the direction perpendicular to the exposure lines may be omitted in the imaging. 
     In Step  7355   d , the receiver designates the area of imaging in the special imaging mode B. By designating a narrower area than the area in which the bright line is captured as the area of imaging, it is possible to keep capturing the bright line even when the imaging direction changes due to hand movement and the like. 
     In Step  7355   e , the receiver detects the movement of the captured image. By moving the area of imaging in the moving direction, it is possible to keep capturing the bright line even when the position of the captured image changes. In Step  7355   f , the receiver obtains the transmitted information from the pattern of the bright line. 
       FIG. 330A  is a diagram for describing yet another imaging mode of the receiver. 
     When the imaging mode is switched from the normal imaging mode to a special imaging mode C, the receiver uses, for imaging, only the exposure lines capturing the subject from among all exposure lines. That is, the receiver uses only the exposure lines  1001  to  2000  for imaging, from time t 1  to time t 4  and from time t 5  to time t 8 . In the special imaging mode C, the exposure lines  1001  to  2000  are exposed in sequence a plurality of times throughout the imaging time of one frame, e.g. from time t 1  to time t 4  or from time t 5  to time t 8 . In addition, in the special imaging mode C, a plurality of images obtained by performing the exposure a plurality of times are not output individually, but one image (image of the same size as the image generated in the normal imaging mode) including the plurality of images is output. The receiver can thus be prevented from missing the reception of the signal from the subject. 
       FIG. 330B  is a flowchart illustrating processing operation of the receiver using the special imaging mode C. 
     First, in Step  7356   a , the receiver detects the part in which the bright line is captured, from the captured image. Next, in Step  7356   b , the receiver sets the hand movement correction function to ON. 
     In Step  7356   c , the receiver switches to the special imaging mode C in which the imaging is performed using only the pixels of the exposure lines in which the bright line is captured. In the special imaging mode C, the imaging is performed only in the area in which the bright line is captured, and the imaging results are arranged to form one image while ignoring the original pixel positions. Here, one or more pixels in the direction perpendicular to the exposure lines may be omitted in the imaging. 
     Since the number of frames output from the imaging unit of the receiver is the same as that in the normal imaging mode, the special imaging mode C is suitable for a receiver that includes a low-performance processor or a receiver that includes a processor also engaged in other processes. 
     In Step  7356   d , the receiver designates the area of imaging in the special imaging mode C. By designating a narrower area than the area in which the bright line is captured as the area of imaging, it is possible to keep capturing the bright line even when the imaging direction changes due to hand movement and the like. 
     In Step  7356   e , the receiver detects the movement of the captured image. By moving the area of imaging in the moving direction, it is possible to keep capturing the bright line even when the position of the captured image changes. In Step  7356   f , the receiver obtains the transmitted information from the pattern of the bright line. 
     Though the information communication method according to one or more aspects has been described by way of the embodiments, the present disclosure is not limited to these embodiments. Other embodiments realized by application of modifications conceivable by those skilled in the art to the embodiments and any combination of the structural elements in the embodiments are also included in the scope of one or more aspects without departing from the subject matter of the present disclosure. 
       FIG. 331A  is a flowchart of an information communication method according to an aspect of the present disclosure. 
     An information communication method according to an aspect of the present disclosure is an information communication method of obtaining information from a subject, and includes steps SA 11 , SA 12 , and SA 13 . 
     In detail, the information communication method includes: an exposure time setting step (SA 11 ) of setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; an imaging step (SA 12 ) of capturing the subject that changes in luminance by the image sensor with the set exposure time, to obtain the image including the bright line; and an information obtainment step (SA 13 ) of obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained image. 
       FIG. 331B  is a block diagram of an information communication device according to an aspect of the present disclosure. 
     An information communication device A 10  according to an aspect of the present disclosure is an information communication device that obtains information from a subject, and includes structural elements A 11 , A 12 , and A 13 . 
     In detail, the information communication device A 10  includes: an exposure time setting unit A 11  that sets an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; an imaging unit A 12  which is the image sensor that captures the subject that changes in luminance by the image sensor with the set exposure time, to obtain the image including the bright line; and a demodulation unit A 13  that obtains the information by demodulating data specified by a pattern of the bright line included in the obtained image. 
       FIG. 331C  is a flowchart of an information communication method according to an aspect of the present disclosure. 
     An information communication method according to an aspect of the present disclosure is an information communication method of obtaining information from a subject, and includes steps SA 21  to SA 26 . 
     In detail, the information communication method includes: a first imaging step (SA 21 ) of obtaining a first image by capturing the subject using an image sensor that includes a plurality of exposure lines; a detection step (SA 22 ) of detecting a range in which the subject is captured, from the first image; a determination step (SA 23 ) of determining, from among the plurality of exposure lines, predetermined exposure lines for capturing the range in which the subject is captured; an exposure time setting step (SA 24 ) of setting an exposure time of the image sensor so that, in a second image obtained using the predetermined exposure lines, a bright line corresponding to the predetermined exposure lines appears according to a change in luminance of the subject; a second imaging step (SA 25 ) of obtaining the second image including the bright line, by capturing the subject that changes in luminance using the predetermined exposure lines with the set exposure time; and an information obtainment step (SA 26 ) of obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained second image. 
       FIG. 331D  is a block diagram of an information communication device according to an aspect of the present disclosure. 
     An information communication device A 20  according to an aspect of the present disclosure is an information communication device that obtains information from a subject, and includes structural elements A 21  to A 26 . 
     In detail, the information communication device A 20  includes: a first image obtainment unit A 21  that obtains a first image by capturing the subject using an image sensor that includes a plurality of exposure lines; a imaging range detection unit A 22  that detects a range in which the subject is captured, from the first image; an exposure line determination unit A 23  that determines, from among the plurality of exposure lines, predetermined exposure lines for capturing the range in which the subject is captured; an exposure time setting unit A 24  that sets an exposure time of the image sensor so that, in a second image obtained using the predetermined exposure lines, a bright line corresponding to the predetermined exposure lines appears according to a change in luminance of the subject; a second image obtainment unit A 25  that obtains the second image including the bright line, by capturing the subject that changes in luminance using the predetermined exposure lines with the set exposure time; and a demodulation unit A 26  that obtains the information by demodulating data specified by a pattern of the bright line included in the obtained second image. 
     Note that the pattern of the bright line mentioned above is synonymous with the difference of the interval of each bright line. 
       FIG. 332  is a diagram illustrating an image obtained by an information communication method according to an aspect of the present disclosure. 
     For example, the exposure time is set to less than 10 milliseconds for the subject that changes in luminance at a frequency greater than or equal to 200 Hz. A plurality of exposure lines included in the image sensor are exposed sequentially, each at a different time. In this case, several bright lines appear in an image obtained by the image sensor, as illustrated in  FIG. 332 . That is, the image includes the bright line parallel to the exposure line. In the information obtainment step (SA 13  or SA 26 ), data specified by a pattern in a direction perpendicular to the exposure line in the pattern of the bright line is demodulated. 
     In the information communication method illustrated in FIG.  331 A and the information communication device A 10  illustrated in  FIG. 331B , the information transmitted using the change in luminance of the subject is obtained by the exposure of the exposure line in the image sensor. This enables communication between various devices, with no need for, for example, a special communication device for wireless communication. Furthermore, in the information communication method illustrated in  FIG. 331C  and the information communication device A 20  illustrated in  FIG. 331D , from among all exposure lines included in the image sensor, only the exposure lines in which the subject is captured are used for obtaining the second image including the bright line, so that the process for the exposure lines in which the subject is not captured can be omitted. This enhances the efficiency of information obtainment, and prevents missing the reception of the information from the subject. 
       FIG. 333A  is a flowchart of an information communication method according to another aspect of the present disclosure. 
     An information communication method according to another aspect of the present disclosure is an information communication method of transmitting a signal using a change in luminance, and includes steps SB 11 , SB 12 , and SB 13 . 
     In detail, the information communication method includes: a determination step (SB 11 ) of determining a pattern of the change in luminance by modulating the signal to be transmitted; a first transmission step (SB 12 ) of transmitting the signal by a light emitter changing in luminance according to the determined pattern; and a second transmission step (SB 13 ) of transmitting the same signal as the signal by the light emitter changing in luminance according to the same pattern as the determined pattern within 33 milliseconds from the transmission of the signal. In the determination step (SB 11 ), the pattern is determined so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. 
       FIG. 333B  is a block diagram of an information communication device according to another aspect of the present disclosure. 
     An information communication device B 10  according to another aspect of the present disclosure is an information communication device that transmits a signal using a change in luminance, and includes structural elements B 11  and B 12 . 
     In detail, the information communication device B 10  includes: a luminance change pattern determination unit B 11  that determines a pattern of the change in luminance by modulating the signal to be transmitted; and a light emitter B 12  that transmits the signal by changing in luminance according to the determined pattern, and transmits the same signal as the signal by changing in luminance according to the same pattern as the determined pattern within 33 milliseconds from the transmission of the signal. The luminance change pattern determination unit B 11  determines the pattern so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. 
     In the information communication method illustrated in  FIG. 333A  and the information communication device B 10  illustrated in  FIG. 333B , the pattern of the change in luminance is determined so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. As a result, the signal can be transmitted using the change in luminance without humans perceiving flicker. Moreover, the same signal is transmitted within 33 milliseconds, ensuring that, even when the receiver receiving the signal has blanking, the signal is transmitted to the receiver. 
       FIG. 334A  is a flowchart of an information communication method according to yet another aspect of the present disclosure. 
     An information communication method according to yet another aspect of the present disclosure is an information communication method of transmitting a signal using a change in luminance, and includes steps SC 11 , SC 12 , SC 13 , and SC 14 . 
     In detail, the information communication method includes: a determination step (SC 11 ) of determining a plurality of frequencies by modulating the signal to be transmitted; a transmission step (SC 12 ) of transmitting the signal by a light emitter changing in luminance according to a constant frequency out of the determined plurality of frequencies; and a change step (SC 14 ) of changing the frequency used for the change in luminance to an other one of the determined plurality of frequencies in sequence, in a period greater than or equal to 33 milliseconds. After the transmission step SC 12 , whether or not all of the determined frequencies have been used for the change in frequency may be determined (SC 13 ), where the update step SC 14  is performed in the case of determining that all of the frequencies have not been used (SC 13 : N). In the transmission step (SC 12 ), the light emitter changes in luminance so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. 
       FIG. 334B  is a block diagram of an information communication device according to yet another aspect of the present disclosure. 
     An information communication device C 10  according to yet another aspect of the present disclosure is an information communication device that transmits a signal using a change in luminance, and includes structural elements C 11 , C 12 , and C 13 . 
     In detail, the information communication device C 10  includes: a frequency determination unit C 11  that determines a plurality of frequencies by modulating the signal to be transmitted; a light emitter C 13  that transmits the signal by changing in luminance according to a constant frequency out of the determined plurality of frequencies; and a frequency change unit C 12  that changes the frequency used for the change in luminance to an other one of the determined plurality of frequencies in sequence, in a period greater than or equal to 33 milliseconds. The light emitter C 13  changes in luminance so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. 
     In the information communication method illustrated in  FIG. 334A  and the information communication device C 10  illustrated in  FIG. 334B , the pattern of the change in luminance is determined so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. As a result, the signal can be transmitted using the change in luminance without humans perceiving flicker. In addition, a lot of FM modulated signals can be transmitted. 
     Moreover, an information communication device may include: an information management unit that manages device information which includes an ID unique to the information communication device and state information of a device; a light emitting element; and a light transmission unit that transmits information using a blink pattern of the light emitting element, wherein when an internal state of the device has changed, the light transmission unit converts the device information into the blink pattern of the light emitting element, and transmits the converted device information. 
     The information communication device may further include an activation history management unit that stores information sensed in the device, the information indicating an activation state of the device or a user usage history, wherein the light transmission unit obtains previously registered performance information of a clock generation device to be utilized, and changes a transmission speed. 
     The light emitting element may include a first light emitting element and a second light emitting element, the second light emitting element being disposed in vicinity of the first light emitting element for transmitting information by blinking, wherein when information transmission is repeatedly performed a certain number of times by the first light emitting element blinking, the second light emitting element emits light during an interval between an end of the information transmission and a start of the information transmission. 
     The information communication device may include: an imaging unit that exposes imaging elements with a time difference; and a signal analysis unit that reads, from one captured image, a change in time-average luminance of an imaging object less than or equal to 1 millisecond, using a difference between exposure times of the imaging elements. 
     The time-average luminance may be time-average luminance greater than or equal to 1/30000 second. 
     The information communication device may further modulate transmission information to a light emission pattern, and transmit the information using the light emission pattern. 
     The information communication device may express a transmission signal by a change in time-average luminance less than or equal to 1 millisecond, and change a light emitting unit in luminance to ensure that time-average luminance greater than or equal to 60 milliseconds is uniform. 
     The information communication device may express the transmission signal by a change in time-average luminance greater than or equal to 1/30000 second. 
     A part common between the transmission signal and a signal expressed by time-average luminance in a same type of information communication device located nearby may be transmitted by causing the light emitting unit to emit light at a same timing as a light emitting unit of the same type of information communication device. 
     A part not common between the transmission signal and the signal expressed by time-average luminance in the same type of information communication device located nearby may be expressed by time-average luminance of the light emitting unit during a time slot in which the same type of information communication device does not express the signal by time-average luminance. 
     The information communication device may include: a first light emitting unit that expresses the transmission signal by a change in time-average luminance; and a second light emitting unit that expresses the transmission signal not by a change in time-average luminance, wherein the signal is transmitted using a position relation between the first light emitting unit and the second light emitting unit. 
     A centralized control device may include a control unit that performs centralized control on any of the information communication devices described above. 
     A building may include any of the information communication devices described above or the centralized control device described above. 
     A train may include any of the information communication devices described above or the centralized control device described above. 
     An imaging device may be an imaging device that captures a two-dimensional image, wherein the image is captured by exposing only an arbitrary imaging element, at a higher speed than in the case where the image is captured by exposing all imaging elements. 
     The arbitrary imaging element may be an imaging element that captures an image of a pixel having a maximum change in time-average luminance less than or equal to 1 millisecond, or a line of imaging elements including the imaging element. 
     Each of the structural elements in each of the above-described embodiments may be configured in the form of an exclusive hardware product, or may be realized by executing a software program suitable for the structural element. Each of the structural elements may be realized by means of a program executing unit, such as a CPU and a processor, reading and executing the software program recorded on a recording medium such as a hard disk or a semiconductor memory. For example, the program causes a computer to execute the information communication method illustrated in any of the flowcharts in  FIGS. 331A, 331C, 333A, and 334A . 
     Summary of Each of the Above Embodiments and Variations 
     An information communication method according to an aspect of the present disclosure is an information communication method of obtaining information from a subject, the information communication method including: a first imaging step of obtaining a first image by capturing the subject using an image sensor that includes a plurality of exposure lines; a detection step of detecting a range in which the subject is captured, from the first image; a determination step of determining, from among the plurality of exposure lines, predetermined exposure lines for capturing the range in which the subject is captured; an exposure time setting step of setting an exposure time of the image sensor so that, in a second image obtained using the predetermined exposure lines, a bright line corresponding to the predetermined exposure lines appears according to a change in luminance of the subject; a second imaging step of obtaining the second image including the bright line, by capturing the subject that changes in luminance using the predetermined exposure lines with the set exposure time; and an information obtainment step of obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained second image. 
     In this way, the information transmitted using the change in luminance of the subject is obtained by the exposure of the exposure line in the image sensor. This enables communication between various devices, with no need for, for example, a special communication device for wireless communication. Besides, from among all exposure lines included in the image sensor, only the exposure lines in which the subject is captured are used for obtaining the second image including the bright line, so that the process for the exposure lines in which the subject is not captured can be omitted. This enhances the efficiency of information obtainment, and prevents missing the reception of the information from the subject. Note that the exposure line is a column or a row of a plurality of pixels that are simultaneously exposed in the image sensor, and the bright line is a line included in a captured image illustrated, for instance, in  FIG. 22 . 
     For example, the predetermined exposure lines may include only exposure lines for capturing the range in which the subject is captured and not include exposure lines for capturing a range in which the subject is not captured, from among the plurality of exposure lines. 
     In this way, it is possible to enhance the efficiency of information obtainment more reliably, and prevent missing the reception of the information from the subject. 
     For example, in the second imaging step, a first imaging time when obtaining the first image may be equally divided by the number of exposure lines included in the predetermined exposure lines to obtain a second imaging time, wherein the second imaging time is set as an imaging time of each exposure line included in the predetermine exposure lines. 
     In this way, the information can be appropriately obtained from the subject which is a transmitter, for instance as illustrated in  FIGS. 328A and 328B . 
     For example, in the second imaging step, an imaging time of each exposure line in the image sensor in the first imaging step may be set as an imaging time of each exposure line included in the predetermined exposure lines. 
     In this way, the information can be appropriately obtained from the subject which is a transmitter, for instance as illustrated in  FIGS. 329A and 329B . 
     For example, in the second imaging step, a plurality of second images obtained using the predetermined exposure lines may be combined to form a third image equal in image size to the first image, wherein in the information obtainment step, the information is obtained by demodulating the data specified by the pattern of the bright line included in the third image. 
     In this way, the information can be appropriately obtained from the subject which is a transmitter, for instance as illustrated in  FIGS. 330A and 330B . 
     For example, in the determination step, exposure lines for capturing a narrower range than the range in which the subject is captured may be determined as the predetermined exposure lines, from among the plurality of exposure lines. 
     In this way, the information can be appropriately obtained from the subject which is a transmitter without being affected by hand movement and the like, for instance as illustrated in  FIGS. 328B, 329B, and 330B . 
     For example, an imaging mode may be switchable between a first mode in which the subject is captured using all of the plurality of exposure lines in the image sensor and a second mode in which the subject is captured using the predetermined exposure lines from among the plurality of exposure lines in the image sensor. 
     In this way, the information can be appropriately obtained from the subject which is a transmitter, by switching the imaging mode. 
     An information communication method according to an aspect of the present disclosure is an information communication method of obtaining information from a subject, the information communication method including: an exposure time setting step of setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; an imaging step of capturing the subject that changes in luminance by the image sensor with the set exposure time, to obtain the image including the bright line; and an information obtainment step of obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained image. 
     In this way, the information transmitted using the change in luminance of the subject is obtained by the exposure of the exposure line in the image sensor. This enables communication between various devices, with no need for, for example, a special communication device for wireless communication. Note that the exposure line is a column or a row of a plurality of pixels that are simultaneously exposed in the image sensor, and the bright line is a line included in a captured image illustrated, for instance, in  FIG. 22 . 
     For example, in the imaging step, a plurality of exposure lines included in the image sensor may be exposed sequentially, each at a different time. 
     In this way, the bright line generated by capturing the subject in a rolling shutter mode is included in the position corresponding to each exposure line in the image, and therefore a lot of information can be obtained from the subject. 
     For example, in the information obtainment step, the data specified by a pattern in a direction perpendicular to the exposure line in the pattern of the bright line may be demodulated. 
     In this way, the information corresponding to the change in luminance can be appropriately obtained. 
     For example, in the exposure time setting step, the exposure time may be set to less than 10 milliseconds. 
     In this way, the bright line can be generated in the image more reliably. 
     For example, in the imaging step, the subject that changes in luminance at a frequency greater than or equal to 200 Hz may be captured. 
     In this way, a lot of information can be obtained from the subject without humans perceiving flicker, for instance as illustrated in  FIGS. 305A and 305B . 
     For example, in the imaging step, the image including the bright line parallel to the exposure line may be obtained. 
     In this way, the information corresponding to the change in luminance can be appropriately obtained. 
     For example, in the information obtainment step, for each area in the obtained image corresponding to a different one of exposure lines included in the image sensor, the data indicating 0 or 1 specified according to whether or not the bright line is present in the area may be demodulated. 
     In this way, a lot of PPM modulated information can be obtained from the subject. For instance as illustrated in  FIG. 22 , in the case of obtaining information based on whether or not each exposure line receives at least a predetermined amount of light, information can be obtained at a speed of fl bits per second at the maximum where f is the number of images per second (frame rate) and l is the number of exposure lines constituting one image. 
     For example, in the information obtainment step, whether or not the bright line is present in the area may be determined according to whether or not a luminance value of the area is greater than or equal to a threshold. 
     In this way, information can be appropriately obtained from the subject. 
     For example, in the imaging step, for each predetermined period, the subject that changes in luminance at a constant frequency corresponding to the predetermined period may be captured, wherein in the information obtainment step, the data specified by the pattern of the bright line generated, for each predetermined period, according to the change in luminance at the constant frequency corresponding to the predetermined period is demodulated. 
     In this way, a lot of FM modulated information can be obtained from the subject. For instance as illustrated in  FIG. 14 , appropriate information can be obtained using a bright line pattern corresponding to a frequency f 1  and a bright line pattern corresponding to a frequency f 2 . 
     For example, in the imaging step, the subject that changes in luminance to transmit a signal by adjusting a time from one change to a next change in luminance may be captured, the one change and the next change being the same one of a rise and a fall in luminance, wherein in the information obtainment step, the data specified by the pattern of the bright line is demodulated, the data being a code associated with the time. 
     In this way, the brightness of the subject (e.g. lighting device) perceived by humans can be adjusted by PWM control without changing the information transmitted from the subject, for instance as illustrated in  FIG. 248 . 
     For example, in the imaging step, the subject that changes in luminance so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range may be captured. 
     In this way, a lot of information can be obtained from the subject without humans perceiving flicker. For instance as illustrated in  FIG. 28 , when a modulated signal “0” indicates no light emission and a modulated signal “1” indicates light emission and there is no bias in a transmission signal, each luminance average obtained by moving averaging is about 75% of the luminance at the time of light emission. This can prevent humans from perceiving flicker. 
     For example, the pattern of the bright line may differ according to the exposure time of the image sensor, wherein in the information obtainment step, the data specified by the pattern corresponding to the set exposure time is demodulated. 
     In this way, different information can be obtained from the subject according to the exposure time, for instance as illustrated in  FIG. 34 . 
     For example, the information communication method may further include detecting a state of an imaging device including the image sensor, wherein in the information obtainment step, the information indicating a position of the subject is obtained, and a position of the imaging device is calculated based on the obtained information and the detected state. 
     In this way, the position of the imaging device can be accurately specified even in the case where GPS or the like is unavailable or more accurately specified than in the case where GPS or the like is used, for instance as illustrated in  FIG. 11 . 
     For example, in the imaging step, the subject that includes a plurality of areas arranged along the exposure line and changes in luminance for each area may be captured. 
     In this way, a lot of information can be obtained from the subject, for instance as illustrated in  FIG. 258 . 
     For example, in the imaging step, the subject that emits a plurality of types of metameric light each at a different time may be captured. 
     In this way, a lot of information can be obtained from the subject without humans perceiving flicker, for instance as illustrated in  FIG. 272 . 
     For example, the information communication method may further include estimating a location where an imaging device including the image sensor is present, wherein in the information obtainment step, identification information of the subject is obtained as the information, and related information associated with the location and the identification information is obtained from a server. 
     In this way, even in the case where the same identification information is transmitted from a plurality of lighting devices using a luminance change, appropriate related information can be obtained according to the location (building) in which the imaging device is present, i.e. the location (building) in which the lighting device is present, for instance as illustrated in  FIGS. 282 and 283 . 
     An information communication method according to an aspect of the present disclosure is an information communication method of transmitting a signal using a change in luminance, the information communication method including: a determination step of determining a pattern of the change in luminance by modulating the signal to be transmitted; a first transmission step of transmitting the signal by a light emitter changing in luminance according to the determined pattern; and a second transmission step of transmitting the same signal as the signal by the light emitter changing in luminance according to the same pattern as the determined pattern within 33 milliseconds from the transmission of the signal, wherein in the determination step, the pattern is determined so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. 
     In this way, the pattern of the change in luminance is determined so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. As a result, the signal can be transmitted using the change in luminance without humans perceiving flicker. Moreover, for instance as illustrated in  FIG. 301B , the same signal is transmitted within 33 milliseconds, ensuring that, even when the receiver receiving the signal has blanking, the signal is transmitted to the receiver. 
     For example, in the determination step, the signal may be modulated by a scheme of modulating a signal expressed by 2 bits to a signal expressed by 4 bits made up of 3 bits each indicating a same value and 1 bit indicating a value other than the same value. 
     In this way, for instance as illustrated in  FIG. 28 , when a modulated signal “0” indicates no light emission and a modulated signal “1” Indicates light emission and there is no bias in a transmission signal, each luminance average obtained by moving averaging is about 75% of the luminance at the time of light emission. This can more reliably prevent humans from perceiving flicker. 
     For example, in the determination step, the pattern of the change in luminance may be determined by adjusting a time from one change to a next change in luminance according to the signal, the one change and the next change being the same one of a rise and a fall in luminance. 
     In this way, the brightness of the light emitter (e.g. lighting device) perceived by humans can be adjusted by PWM control without changing the transmission signal, for instance as illustrated in  FIG. 248 . 
     For example, in the first transmission step and the second transmission step, the light emitter may change in luminance so that a signal different according to an exposure time of an image sensor that captures the light emitter changing in luminance is obtained by an imaging device including the image sensor. 
     In this way, different signals can be transmitted to the imaging device according to the exposure time, for instance as illustrated in  FIG. 34 . 
     For example, in the first transmission step and the second transmission step, a plurality of light emitters may change in luminance synchronously to transmit common information, wherein after the transmission of the common information, each light emitter changes in luminance individually to transmit information different depending on the light emitter. 
     In this way, for instance as illustrated in  FIG. 41 , when the plurality of light emitters simultaneously transmit the common information, the plurality of light emitters can be regarded as one large light emitter. Such a light emitter is captured in a large size by the imaging device receiving the common information, so that information can be transmitted faster from a longer distance. Moreover, for instance as illustrated in  FIG. 12A , by the plurality of light emitters transmitting the common information, it is possible to reduce the amount of individual information transmitted from each light emitter. 
     For example, the information communication method may further include an instruction reception step of receiving an instruction of whether or not to modulate the signal, wherein the determination step, the first transmission step, and the second transmission step are performed in the case where an instruction to modulate the signal is received, and the light emitter emits light or stops emitting light without the determination step, the first transmission step, and the second transmission step being performed in the case where an instruction not to modulate the signal is received. 
     In this way, whether or not to perform modulation is switched, with it being possible to reduce the noise effect on luminance changes of other light emitters, for instance as illustrated in  FIG. 12A . 
     For example, the light emitter may include a plurality of areas arranged along an exposure line of an image sensor that captures the light emitter, wherein in the first transmission step and the second transmission step, the light emitter changes in luminance for each area. 
     In this way, a lot of information can be transmitted, for instance as illustrated in  FIG. 258 . 
     For example, in the first transmission step and the second transmission step, the light emitter may change in luminance by emitting a plurality of types of metameric light each at a different time. 
     In this way, a lot of information can be transmitted without humans perceiving flicker, for instance as illustrated in  FIG. 272 . 
     For example, in the first transmission step and the second transmission step, identification information of the light emitter may be transmitted as the signal or the same signal. 
     In this way, the identification information of the light emitter is transmitted, for instance as illustrated in  FIG. 282 . The imaging device receiving the identification information can obtain more information associated with the identification information from a server or the like via a communication line such as the Internet. 
     An information communication method according to an aspect of the present disclosure is an information communication method of transmitting a signal using a change in luminance, the information communication method including: a determination step of determining a plurality of frequencies by modulating the signal to be transmitted; a transmission step of transmitting the signal by a light emitter changing in luminance according to a constant frequency out of the determined plurality of frequencies; and a change step of changing the frequency used for the change in luminance to an other one of the determined plurality of frequencies in sequence, in a period greater than or equal to 33 milliseconds, wherein in the transmission step, the light emitter changes in luminance so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. 
     In this way, the pattern of the change in luminance is determined so that each average obtained by moving-averaging the changing luminance with a width greater than or equal to 5 milliseconds is within a predetermined range. As a result, the signal can be transmitted using the change in luminance without humans perceiving flicker. Moreover, a lot of FM modulated signals can be transmitted. For instance as illustrated in  FIG. 14 , appropriate information can be transmitted by changing the luminance change frequency (f 1 , f 2 , etc.) in a period greater than or equal to 33 milliseconds. 
     Embodiment 14 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as a blink pattern of an LED, an organic EL device, or the like in Embodiments 1 to 13 described above. 
       FIG. 335  is a diagram illustrating an example of each mode of a receiver in this embodiment. 
     In the normal imaging mode, a receiver  8000  performs imaging at a shutter speed of 1/100 second as an example to obtain a normal captured image, and displays the normal captured image on a display. For example, a subject such as a street lighting or a signage as a store sign and its surroundings are clearly shown in the normal captured image. 
     In the visible light communication mode, the receiver  8000  performs imaging at a shutter speed of 1/10000 second as an example, to obtain a visible light communication image. For example, in the case where the above-mentioned street lighting or signage is transmitting a signal by a luminance change as the transmitter described in any of Embodiments 1 to 13, one or more bright lines (hereafter referred to as “bright line pattern”) are shown in the signal transmission part of the visible light communication image, while nothing is shown in the other part. That is, in the visible light communication image, only the bright line pattern is shown and the part of the subject not changing in luminance and the surroundings of the subject are not shown. 
     In the intermediate mode, the receiver  8000  performs imaging at a shutter speed of 1/3000 second as an example, to obtain an intermediate image. In the intermediate image, the bright line pattern is shown, and the part of the subject not changing in luminance and the surroundings of the subject are shown, too. By the receiver  8000  displaying the intermediate image on the display, the user can find out from where or from which position the signal is being transmitted. Note that the bright line pattern, the subject, and its surroundings shown in the intermediate image are not as clear as the bright line pattern in the visible light communication image and the subject and its surroundings in the normal captured image respectively, but have the level of clarity recognizable by the user. 
     In the following description, the normal imaging mode or imaging in the normal imaging mode is referred to as “normal imaging”, and the visible light communication mode or imaging in the visible light communication mode is referred to as “visible light imaging” (visible light communication). Imaging in the intermediate mode may be used instead of normal imaging and visible light imaging, and the intermediate image may be used instead of the below-mentioned synthetic image. 
       FIG. 336  is a diagram illustrating an example of imaging operation of a receiver in this embodiment. 
     The receiver  8000  switches the imaging mode in such a manner as normal imaging, visible light communication, normal imaging, . . . . The receiver  8000  synthesizes the normal captured image and the visible light communication image to generate a synthetic image in which the bright line pattern, the subject, and its surroundings are clearly shown, and displays the synthetic image on the display. The synthetic image is an image generated by superimposing the bright line pattern of the visible light communication image on the signal transmission part of the normal captured image. The bright line pattern, the subject, and its surroundings shown in the synthetic image are clear, and have the level of clarity sufficiently recognizable by the user. Displaying such a synthetic image enables the user to more distinctly find out from which position the signal is being transmitted. 
       FIG. 337  is a diagram illustrating another example of imaging operation of a receiver in this embodiment. 
     The receiver  8000  includes a camera Ca 1  and a camera Ca 2 . In the receiver  8000 , the camera Ca 1  performs normal imaging, and the camera Ca 2  performs visible light imaging. Thus, the camera Ca 1  obtains the above-mentioned normal captured image, and the camera Ca 2  obtains the above-mentioned visible light communication image. The receiver  8000  synthesizes the normal captured image and the visible light communication image to generate the above-mentioned synthetic image, and displays the synthetic image on the display. 
       FIG. 338A  is a diagram illustrating another example of imaging operation of a receiver in this embodiment. 
     In the receiver  8000  including two cameras, the camera Ca 1  switches the imaging mode in such a manner as normal imaging, visible light communication, normal imaging, . . . . Meanwhile, the camera Ca 2  continuously performs normal imaging. When normal imaging is being performed by the cameras Ca 1  and Ca 2  simultaneously, the receiver  8000  estimates the distance (hereafter referred to as “subject distance”) from the receiver  8000  to the subject based on the normal captured images obtained by these cameras, through the use of stereoscopy (triangulation principle). By using such estimated subject distance, the receiver  8000  can superimpose the bright line pattern of the visible light communication image on the normal captured image at the appropriate position. The appropriate synthetic image can be generated in this way. 
       FIG. 338B  is a diagram illustrating another example of imaging operation of a receiver in this embodiment. 
     The receiver  8000  includes three cameras (cameras Ca 1 , Ca 2 , and Ca 3 ) as an example. In the receiver  8000 , two cameras (cameras Ca 2  and Ca 3 ) continuously perform normal imaging, and the remaining camera (camera Ca 1 ) continuously performs visible light communication. Hence, the subject distance can be estimated at any timing, based on the normal captured images obtained by two cameras engaged in normal imaging. 
       FIG. 338C  is a diagram illustrating another example of imaging operation of a receiver in this embodiment. 
     The receiver  8000  includes three cameras (cameras Ca 1 , Ca 2 , and Ca 3 ) as an example. In the receiver  8000 , each camera switches the imaging mode in such a manner as normal imaging, visible light communication, normal imaging, . . . . The imaging mode of each camera is switched per period so that, in one period, two cameras perform normal imaging and the remaining camera performs visible light communication. That is, the combination of cameras engaged in normal imaging is changed periodically. Hence, the subject distance can be estimated in any period, based on the normal captured images obtained by two cameras engaged in normal imaging. 
       FIG. 339A  is a diagram illustrating an example of camera arrangement of a receiver in this embodiment. 
     In the case where the receiver  8000  includes two cameras Ca 1  and Ca 2 , the two cameras Ca 1  and Ca 2  are positioned away from each other as illustrated in  FIG. 339A . The subject distance can be accurately estimated in this way. In other words, the subject distance can be estimated more accurately when the distance between two cameras is longer. 
     In the case where the receiver  8000  includes three cameras Ca 1 , Ca 2 , and Ca 3 , the two cameras Ca 1  and Ca 2  for normal imaging are positioned away from each other as illustrated in  FIG. 339B , and the camera Ca 3  for visible light communication is, for example, positioned between the cameras Ca 1  and Ca 2 . The subject distance can be accurately estimated in this way. In other words, the subject distance can be accurately estimated by using two farthest cameras for normal imaging. 
       FIG. 340  is a diagram illustrating an example of display operation of a receiver in this embodiment. 
     The receiver  8000  switches the imaging mode in such a manner as visible light communication, normal imaging, visible light communication, . . . , as mentioned above. Upon performing visible light communication first, the receiver  8000  starts an application program. The receiver  8000  then estimates its position based on the signal received by visible light communication, as described in Embodiments 1 to 13. Next, when performing normal imaging, the receiver  8000  displays AR (Augmented Reality) information on the normal captured image obtained by normal imaging. The AR information is obtained based on, for example, the position estimated as mentioned above. The receiver  8000  also estimates the change in movement and direction of the receiver  8000  based on the detection result of the 9-axis sensor, the motion detection in the normal captured image, and the like, and moves the display position of the AR information according to the estimated change in movement and direction. This enables the AR information to follow the subject image in the normal captured image. 
     When switching the imaging mode from normal imaging to visible light communication, in visible light communication the receiver  8000  superimposes the AR information on the latest normal captured image obtained in immediately previous normal imaging. The receiver  8000  then displays the normal captured image on which the AR information is superimposed. The receiver  8000  also estimates the change in movement and direction of the receiver  8000  based on the detection result of the 9-axis sensor, and moves the AR information and the normal captured image according to the estimated change in movement and direction, in the same way as in normal imaging. This enables the AR information to follow the subject image in the normal captured image according to the movement of the receiver  8000  and the like in visible light communication, as in normal imaging. Moreover, the normal image can be enlarged or reduced according to the movement of the receiver  8000  and the like. 
       FIG. 341  is a diagram illustrating an example of display operation of a receiver in this embodiment. 
     For example, the receiver  8000  may display the synthetic image in which the bright line pattern is shown, as illustrated in (a) in  FIG. 341 . As an alternative, the receiver  8000  may superimpose, instead of the bright line pattern, a signal specification object which is an image having a predetermined color for notifying signal transmission on the normal captured image to generate the synthetic image, and display the synthetic image, as illustrated in (b) in  FIG. 341 . 
     As another alternative, the receiver  8000  may display, as the synthetic image, the normal captured image in which the signal transmission part is indicated by a dotted frame and an identifier (e.g. ID:  101 , ID:  102 , etc.), as illustrated in (c) in  FIG. 341 . As another alternative, the receiver  8000  may superimpose, instead of the bright line pattern, a signal identification object which is an image having a predetermined color for notifying transmission of a specific type of signal on the normal captured image to generate the synthetic image, and display the synthetic image, as illustrated in (d) in  FIG. 341 . In this case, the color of the signal identification object differs depending on the type of signal output from the transmitter. For example, a red signal identification object is superimposed in the case where the signal output from the transmitter is position information, and a green signal identification object is superimposed in the case where the signal output from the transmitter is a coupon. 
       FIG. 342  is a diagram illustrating an example of operation of a receiver in this embodiment. 
     For example, in the case of receiving the signal by visible light communication, the receiver  8000  may output a sound for notifying the user that the transmitter has been discovered, while displaying the normal captured image. In this case, the receiver  8000  may change the type of output sound, the number of outputs, or the output time depending on the number of discovered transmitters, the type of received signal, the type of information specified by the signal, or the like. 
       FIG. 343  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, when the user touches the bright line pattern shown in the synthetic image, the receiver  8000  generates an information notification image based on the signal transmitted from the subject corresponding to the touched bright line pattern, and displays the information notification image. The information notification image indicates, for example, a coupon or a location of a store. The bright line pattern may be the signal specification object, the signal identification object, or the dotted frame illustrated in  FIG. 341 . The same applies to the below-mentioned bright line pattern. 
       FIG. 344  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, when the user touches the bright line pattern shown in the synthetic image, the receiver  8000  generates an information notification image based on the signal transmitted from the subject corresponding to the touched bright line pattern, and displays the information notification image. The information notification image indicates, for example, the current position of the receiver  8000  by a map or the like. 
       FIG. 345  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, the receiver  8000  receives signals from two street lightings which are subjects as transmitters. The receiver  8000  estimates the current position of the receiver  8000  based on these signals, as in Embodiments 1 to 13. The receiver  8000  then displays the normal captured image, and also superimposes an information notification image (an image showing latitude, longitude, and the like) indicating the estimation result on the normal captured image. The receiver  8000  may also display an auxiliary information notification image on the normal captured image. For instance, the auxiliary information notification image prompts the user to perform an operation for calibrating the 9-axis sensor (particularly the geomagnetic sensor), i.e. an operation for drift cancellation. As a result of such an operation, the current position can be estimated with high accuracy. 
     When the user touches the displayed information notification image, the receiver  8000  may display the map showing the estimated position, instead of the normal captured image. 
       FIG. 346  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, when the user swipes on the receiver  8000  on which the synthetic image is displayed, the receiver  8000  displays the normal captured image including the dotted frame and the identifier like the normal captured image illustrated in (c) in  FIG. 341 , and also displays a list of information to follow the swipe operation. The list includes information specified by the signal transmitted from the part (transmitter) identified by each identifier. The swipe may be, for example, an operation of moving the user&#39;s finger from outside the display of the receiver  8000  on the right side into the display. The swipe may be an operation of moving the user&#39;s finger from the top, bottom, or left side of the display into the display. 
     When the user taps information included in the list, the receiver  8000  may display an information notification image (e.g. an image showing a coupon) indicating the information in more detail. 
       FIG. 347  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, when the user swipes on the receiver  8000  on which the synthetic image is displayed, the receiver  8000  superimposes an information notification image on the synthetic image, to follow the swipe operation. The information notification image indicates the subject distance with an arrow so as to be easily recognizable by the user. The swipe may be, for example, an operation of moving the user&#39;s finger from outside the display of the receiver  8000  on the bottom side into the display. The swipe may be an operation of moving the user&#39;s finger from the left, top, or right side of the display into the display. 
       FIG. 348  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, the receiver  8000  captures, as a subject, a transmitter which is a signage showing a plurality of stores, and displays the normal captured image obtained as a result. When the user taps a signage image of one store included in the subject shown in the normal captured image, the receiver  8000  generates an information notification image based on the signal transmitted from the signage of the store, and displays an information notification image  8001 . The information notification image  8001  is, for example, an image showing the availability of the store and the like. 
       FIG. 349  is a diagram illustrating an example of operation of a receiver, a transmitter, and a server in this embodiment. 
     A transmitter  8012  as a television transmits a signal to a receiver  8011  by a luminance change. The signal includes information prompting the user to buy content relating to a program being viewed. Having received the signal by visible light communication, the receiver  8011  displays an information notification image prompting the user to buy content, based on the signal. When the user performs an operation for buying the content, the receiver  8011  transmits at least one of information included in a SIM (Subscriber Identity Module) card inserted in the receiver  8011 , a user ID, a terminal ID, credit card information, charging information, a password, and a transmitter ID, to a server  8013 . The server  8013  manages a user ID and payment information in association with each other, for each user. The server  8013  specifies a user ID based on the information transmitted from the receiver  8011 , and checks payment information associated with the user ID. By this check, the server  8013  determines whether or not to permit the user to buy the content. In the case of determining to permit the user to buy the content, the server  8013  transmits permission information to the receiver  8011 . Having received the permission information, the receiver  8011  transmits the permission information to the transmitter  8012 . Having received the permission information, the transmitter  8012  obtains the content via a network as an example, and reproduces the content. 
     The transmitter  8012  may transmit information including the ID of the transmitter  8012  to the receiver  8011 , by a luminance change. In this case, the receiver  8011  transmits the information to the server  8013 . Having obtained the information, the server  8013  can determine that, for example, the television program is being viewed on the transmitter  8012 , and conduct television program rating research. 
     The receiver  8011  may include information of an operation (e.g. voting) performed by the user in the above-mentioned information and transmit the information to the server  8013 , to allow the server  8013  to reflect the information on the television program. An audience participation program can be realized in this way. Besides, in the case of receiving a post from the user, the receiver  8011  may include the post in the above-mentioned information and transmit the information to the server  8013 , to allow the server  8013  to reflect the post on the television program, a network message board, or the like. 
     Furthermore, by the transmitter  8012  transmitting the above-mentioned information, the server  8013  can charge for television program viewing by paid broadcasting or on-demand TV. The server  8013  can also cause the receiver  8011  to display an advertisement, or the transmitter  8012  to display detailed information of the displayed television program or an URL of a site showing the detailed information. The server  8013  may also obtain the number of times the advertisement is displayed on the receiver  8011 , the price of a product bought from the advertisement, or the like, and charge the advertiser according to the number of times or the price. Such price-based charging is possible even in the case where the user seeing the advertisement does not buy the product immediately. When the server  8013  obtains information indicating the manufacturer of the transmitter  8012  from the transmitter  8012  via the receiver  8011 , the server  8013  may provide a service (e.g. payment for selling the product) to the manufacturer indicated by the information. 
       FIG. 350  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, the user points a camera of a receiver  8021  at a plurality of transmitters  8020   a  to  8020   d  as lightings. Here, the receiver  8021  is moved so that the transmitters  8020   a  to  8020   d  are sequentially captured as a subject. By performing visible light communication during the movement, the receiver  8021  receives a signal from each of the transmitters  8020   a  to  8020   d . The signal includes information indicating the position of the transmitter. The receiver  8021  estimates the position of the receiver  8021  using the triangulation principle, based on the positions indicated by the signals received from the transmitters  8020   a  to  8020   d , the detection result of the 9-axis sensor included in the receiver  8021 , and the movement of the captured image. In this case, the drift of the 9-axis sensor (particularly the geomagnetic sensor) is canceled by moving the receiver  8021 , so that the position can be estimated with higher accuracy. 
       FIG. 351  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     For example, a receiver  8030  is a head-mounted display including a camera. When a start button is pressed, the receiver  8030  starts imaging in the visible light communication mode, i.e. visible light communication. In the case of receiving a signal by visible light communication, the receiver  8030  notifies the user of information corresponding to the received signal. The notification is made, for example, by outputting a sound from a speaker included in the receiver  8030 , or by displaying an image. Visible light communication may be started not only when the start button is pressed, but also when the receiver  8030  receives a sound instructing the start or when the receiver  8030  receives a signal instructing the start by wireless communication. Visible light communication may also be started when the change width of the value obtained by a 9-axis sensor included in the receiver  8030  exceeds a predetermined range or when a bright line pattern, even if only slightly, appears in the normal captured image. 
       FIG. 352  is a diagram illustrating an example of initial setting of a receiver in this embodiment. 
     The receiver  8030  displays an alignment image  8031  upon initial setting. The alignment image  8031  is used to align the position pointed by the user in the image captured by the camera of the receiver  8030  and the image displayed on the receiver  8030 . When the user places his or her fingertip at the position of a circle shown in the alignment image  8031 , the receiver associates the position of the fingertip and the position of the circle, and performs alignment. That is, the position pointed by the user is calibrated. 
       FIG. 353  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  specifies a signal transmission part by visible light communication, and displays a synthetic image  8034  in which a bright line pattern is shown in the part. The user performs an operation such as a tap or a double tap, on the bright line pattern. The receiver  8030  receives the operation, specifies the bright line pattern subjected to the operation, and displays an information notification image  8032  based on a signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 354  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays the synthetic image  8034  in the same way as above. The user performs an operation of moving his or her fingertip so as to encircle the bright line pattern in the synthetic image  8034 . The receiver  8030  receives the operation, specifies the bright line pattern subjected to the operation, and displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 355  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays the synthetic image  8034  in the same way as above. The user performs an operation of placing his or her fingertip at the bright line pattern in the synthetic image  8034  for a predetermined time or more. The receiver  8030  receives the operation, specifies the bright line pattern subjected to the operation, and displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 356  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays the synthetic image  8034  in the same way as above. The user performs an operation of moving his or her fingertip toward the bright line pattern in the synthetic image  8034  by a swipe. The receiver  8030  receives the operation, specifies the bright line pattern subjected to the operation, and displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 357  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays the synthetic image  8034  in the same way as above. The user performs an operation of continuously directing his or her gaze to the bright line pattern in the synthetic image  8034  for a predetermined time or more. Alternatively, the user performs an operation of blinking a predetermined number of times while directing his or her gaze to the bright line pattern. The receiver  8030  receives the operation, specifies the bright line pattern subjected to the operation, and displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 358  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays the synthetic image  8034  in the same way as above, and also displays an arrow associated with each bright line pattern in the synthetic image  8034 . The arrow of each bright line pattern differs in direction. The user performs an operation of moving his or her head along one of the arrows. The receiver  8030  receives the operation based on the detection result of the 9-axis sensor, and specifies the bright line pattern associated with the arrow corresponding to the operation, i.e. the arrow in the direction in which the head is moved. The receiver  8030  displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 359A  is a diagram illustrating a pen used to operate a receiver in this embodiment. 
     A pen  8033  includes a transmitter  8033   a  for transmitting a signal by a luminance change, and buttons  8033   b  and  8033   c . When the button  8033   b  is pressed, the transmitter  8033   a  transmits a predetermined first signal. When the button  8033   c  is pressed, the transmitter  8033   a  transmits a predetermined second signal different from the first signal. 
       FIG. 359B  is a diagram illustrating operation of a receiver using a pen in this embodiment. 
     The pen  8033  is used instead of the user&#39;s finger mentioned above, like a stylus pen. By selective use of the buttons  8033   b  and  8033   c , the pen  8033  can be used like a normal pen or an eraser. 
       FIG. 360  is a diagram illustrating an example of appearance of a receiver in this embodiment. 
     The receiver  8030  includes a first touch sensor  8030   a  and a second touch sensor  8030   b . These touch sensors are attached to the frame of the receiver  8030 . For example, when the user places his or her fingertip on the first touch sensor  8030   a  and moves the fingertip, the receiver  8030  moves the pointer in the image displayed to the user, according to the movement of the fingertip. When the user touches the second touch sensor  8030   b , the receiver  8030  selects the object pointed by the pointer in the image displayed to the user. 
       FIG. 361  is a diagram illustrating another example of appearance of a receiver in this embodiment. 
     The receiver  8030  includes a touch sensor  8030   c . The touch sensor  8030   c  is attached to the frame of the receiver  8030 . For example, when the user places his or her fingertip on the touch sensor  8030   c  and moves the fingertip, the receiver  8030  moves the pointer in the image displayed to the user, according to the movement of the fingertip. When the user presses the touch sensor  8030   c , the receiver  8030  selects the object pointed by the pointer in the image displayed to the user. The touch sensor  8030   c  is thus realized as a clickable touch sensor. 
       FIG. 362  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays the synthetic image  8034  in the same way as above, and also displays a pointer  8035  in the synthetic image  8034 . In the case where the receiver  8030  includes the first touch sensor  8030   a  and the second touch sensor  8030   b , the user places his or her fingertip on the first touch sensor  8030   a  and moves the fingertip, to move the pointer to the object as the bright line pattern. The user then touches the second touch sensor  8030   b , to cause the receiver  8030  to select the bright line pattern. Having selected the bright line pattern, the receiver  8030  displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
     In the case where the receiver  8030  includes the touch sensor  8030   c , the user places his or her fingertip on the touch sensor  8030   c  and moves the fingertip, to move the pointer to the object as the bright line pattern. The user then presses the touch sensor  8030   c , to cause the receiver  8030  to select the bright line pattern. Having selected the bright line pattern, the receiver  8030  displays the information notification image  8032  based on the signal transmitted from the part corresponding to the bright line pattern. 
       FIG. 363A  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays a gesture confirmation image  8036  based on a signal obtained by visible light communication. The gesture confirmation image  8036  prompts the user to make a predetermined gesture, to provide a service to the user as an example. 
       FIG. 363B  is a diagram illustrating an example of application using a receiver in this embodiment. 
     A user  8038  carrying the receiver  8030  is in a shop or the like. Here, the receiver  8030  displays the above-mentioned gesture confirmation image  8036  to the user  8038 . The user  8038  makes the predetermined gesture according to the gesture confirmation image  8036 . A staff  8039  in the shop carries a receiver  8037 . The receiver  8037  is a head-mounted display including a camera, and may have the same structure as the receiver  8030 . The receiver  8037  displays the gesture confirmation image  8036  based on a signal obtained by visible light communication, too. The staff  8039  determines whether or not the predetermined gesture indicated by the displayed gesture confirmation image  8036  and the gesture made by the user  8038  match. In the case of determining that the predetermined gesture and the gesture made by the user  8038  match, the staff  8039  provides the service associated with the gesture confirmation image  8036 , to the user  8038 . 
       FIG. 364A  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8030  displays a gesture confirmation image  8040  based on a signal obtained by visible light communication. The gesture confirmation image  8040  prompts the user to make a predetermined gesture, to permit wireless communication as an example. 
       FIG. 364B  is a diagram illustrating an example of application using a receiver in this embodiment. 
     The user  8038  carries the receiver  8030 . Here, the receiver  8030  displays the above-mentioned gesture confirmation image  8040  to the user  8038 . The user  8038  makes the predetermined gesture according to the gesture confirmation image  8040 . A person around the user  8038  carries the receiver  8037 . The receiver  8037  is a head-mounted display including a camera, and may have the same structure as the receiver  8030 . The receiver  8037  captures the predetermined gesture made by the user  8038 , to obtain authentication information such as a password included in the gesture. In the case where the receiver  8037  determines that the authentication information matches predetermined information, the receiver  8037  establishes wireless connection with the receiver  8030 . Subsequently, the receivers  8030  and  8037  can wirelessly communicate with each other. 
       FIG. 365A  is a diagram illustrating an example of operation of a transmitter in this embodiment. 
     The transmitter alternately transmits signals  1  and  2 , for example in a predetermined period. The transmission of the signal  1  and the transmission of the signal  2  are each carried out by a luminance change such as blinking of visible light. A luminance change pattern for transmitting the signal  1  and a luminance change pattern for transmitting the signal  2  are different from each other. 
       FIG. 365B  is a diagram illustrating another example of operation of a transmitter in this embodiment. 
     The transmitter may transmit the signals  1  and  2  intermittently with a buffer time, instead of continuously transmitting the signals  1  and  2  as mentioned above. In the buffer time, the transmitter does not change in luminance. Alternatively, in the buffer time, the transmitter may transmit a signal indicating that the transmitter is in the buffer time by a luminance change, or perform a luminance change different from the luminance change for transmitting the signal  1  or the luminance change for transmitting the signal  2 . This enables the receiver to appropriately receive the signals  1  and  2  without interference. 
       FIG. 366  is a diagram illustrating another example of operation of a transmitter in this embodiment. 
     The transmitter repeatedly transmits a signal sequence made up of a preamble, a block  1 , a block  2 , a block  3 , and a check signal, by a luminance change. The block  1  includes a preamble, an address  1 , data  1 , and a check signal. The blocks  2  and  3  each have the same structure as the block  1 . Specific information is obtained by using data included in the blocks  1 ,  2 , and  3 . 
     In detail, in the above-mentioned signal sequence, one set of data or information is stored in a state of being divided into three blocks. Accordingly, even when a receiver that needs a blanking time for imaging as described in Embodiments 1 to 13 cannot receive all data of the blocks  1 ,  2 , and  3  from one signal sequence, the receiver can receive the remaining data from another signal sequence. As a result, even a receiver that needs a blanking time can appropriately obtain the specific information from at least one signal sequence. 
     In the above-mentioned signal sequence, a preamble and a check signal are provided for a set of three blocks. Hence, a receiver capable of receiving light without needing a blanking time, such as a receiver including an illuminance sensor, can receive one signal sequence at one time through the use of the preamble and the check signal provided for the set, thus obtaining the specific information in a short time. 
       FIG. 367  is a diagram illustrating another example of operation of a transmitter in this embodiment. 
     When repeatedly transmitting the signal sequence including the blocks  1 ,  2 , and  3  as described above, the transmitter may change, for each signal sequence, the order of the blocks included in the signal sequence. For example, the blocks  1 ,  2 , and  3  are included in this order in the first signal sequence, and the blocks  3 ,  1 , and  2  are included in this order in the next signal sequence. A receiver that requires a periodic blanking time can therefore avoid obtaining only the same block. 
       FIG. 368  is a diagram illustrating an example of communication form between a plurality of transmitters and a receiver in this embodiment. 
     A receiver  8050  may receive signals (visible light) transmitted from transmitters  8051   a  and  8051   b  as lightings and reflected by a reflection surface. The receiver  8050  can thus receive signals from many transmitters all together. In this case, the transmitters  8051   a  and  8051   b  transmit signals of different frequencies or protocols. As a result, the receiver  8050  can receive the signals from the transmitters without interference. 
       FIG. 369  is a diagram illustrating an example of operation of a plurality of transmitters in this embodiment. 
     One of the transmitters  8051   a  and  8051   b  may monitor the signal transmission state of the other transmitter, and transmit a signal to avoid interference with a signal of the other transmitter. For instance, one transmitter receives a signal transmitted from the other transmitter, and transmits a signal of a protocol different from the received signal. Alternatively, one transmitter detects a time period during which no signal is transmitted from the other transmitter, and transmits a signal during the time period. 
       FIG. 370  is a diagram illustrating another example of communication form between a plurality of transmitters and a receiver in this embodiment. 
     The transmitters  8051   a  and  8051   b  may transmit signals of the same frequency or protocol. In this case, the receiver  8050  specifies the strength of the signal transmitted from each of the transmitters, i.e. the edge strength of the bright line included in the captured image. The strength is lower when the distance between the receiver  8050  and the transmitter is longer. In the case where the distance between the receiver  8050  and the transmitter  8051   a  and the distance between the receiver  8050  and the transmitter  8051   b  are different from each other, the difference in distance can be exploited in this way. Thus, the receiver  8050  can separately receive the signals transmitted from the transmitters  8051   a  and  8051   b  appropriately, according to the specified strengths. 
       FIG. 371  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     The receiver  8050  receives a signal transmitted from the transmitter  8051   a  and reflected by a reflection surface. Here, the receiver  8050  may estimate the position of the transmitter  8051   a , based on the strength distribution of luminance (the difference in luminance between a plurality of positions) in the captured image. 
       FIG. 372  is a diagram illustrating an example of application of a receiver in this embodiment. 
     A receiver  7510   a  such as a smartphone captures a light source  7510   b  by a back camera (out camera)  7510   c  to receive a signal transmitted from the light source  7510   b , and obtains the position and direction of the light source  7510   b  from the received signal. The receiver  7510   a  estimates the position and direction of the receiver  7510   a , from the state of the light source  7510   b  in the captured image and the sensor value of the 9-axis sensor included in the receiver  7510   a . The receiver  7510   a  captures a user  7510   e  by a front camera (face camera, in camera)  7510   f , and estimates the position and direction of the head and the gaze direction (the position and direction of the eye) of the user  7510   e  by image processing. The receiver  7510   a  changes the behavior (display content or playback sound) according to the gaze direction of the user  7510   e . the imaging by the back camera  7510   c  and the imaging by the front camera  7510   f  may be performed simultaneously or alternately. 
       FIG. 373  is a diagram illustrating an example of application of a receiver in this embodiment. 
     Receivers  7511   d  and  7511   i  such as smartphones respectively receive signals from light sources  7511   b  and  7511   g , estimate the positions and directions of the receivers  7511   d  and  7511   i , and estimate the gaze directions of users  7511   e  and  7511   i , as in the above-mentioned way. The receivers  7511   d  and  7511   i  respectively obtain information of surrounding objects  7511   a  to  7511   c  and  7511   f  to  7511   h  from a server, based on the received data. The receivers  7511   d  and  7511   i  change their display contents as if the users can see the objects on the opposite side through the receivers  7511   d  and  7511   i . The receivers  7511   d  and  7511   i  display an AR (Augmented Reality) object such as  7511   k , according to the display contents. When the gaze of the user  7511   j  exceeds the imaging range of the camera, the receiver  7511   i  displays that the range is exceeded, as in  7511   i . As an alternative, the receiver  7511   i  displays an AR object or other information in the area outside the range. As another alternative, the receiver  7511   i  displays a previously captured image in the area outside the range in a state of being connected to the current image. 
       FIG. 374  is a diagram illustrating an example of application of a receiver in this embodiment. 
     A receiver  7512   c  such as a smartphone receives a signal from a light source  7512   a , estimates the position and direction of the receiver  7512   c , and estimates the gaze direction of a user  7512   d , as in the above-mentioned way. The receiver  7512   c  performs a process relating to an object  7512   b  in the gaze direction of the user  7512   d . For example, the receiver  7512   c  displays information about the object  7512   b  on the screen. When the gaze direction of a user  7512   h  moves from an object  7512   f  to a receiver  7512   g , the receiver  7512   g  determines that the user  7512   h  is interested in the object  7512   h , and continues the process relating to the object  7512   h . For example, the receiver  7512   g  keeps displaying the information of the object  7512   f  on the screen. 
       FIG. 375  is a diagram illustrating an example of application of a transmitter in this embodiment. 
     A transmitter  7513   a  such as a lighting is high in luminance. Regardless of whether the luminance is high or low as a transmission signal, the transmitter  7513   a  captured by a receiver exceeds an upper limit of brightness, and as a result no bright line appears as in  7513   b . Accordingly, a transmitter  7513   c  includes a part  7513   d  such as a diffusion plate or a prism for diffusing or weakening light, to reduce the luminance. As a result, the receiver can capture bright lines as in  7513   e.    
       FIG. 376  is a diagram illustrating an example of application of a transmitter in this embodiment. 
     A transmitter  7514   a  such as a lighting does not have a uniform light source, and so the luminance is not uniform in a captured image  7514   b , causing a reception error. Accordingly, a transmitter  7514   c  includes a part  7514   d  such as a diffusion plate or a prism for diffusing light, to attain uniform luminance as in  7514   c . A reception error can be prevented in this way. 
       FIG. 377  is a diagram illustrating an example of application of a reception method in this embodiment. 
     Transmitters  7515   a  and  7515   b  are each high in luminance in the center part, so that bright lines appear not in the center part but in the peripheral part in an image captured by a receiver. Since the bright lines are discontinuous, the receiver cannot receive a signal from a part  7515   d , but can receive a signal from a part  7515   c . By reading bright lines along a path  7515   e , the receiver can receive a signal from more bright lines than in the part  7515   c.    
       FIG. 378  is a diagram illustrating an example of application of a transmitter in this embodiment. 
     Transmitters  7516   a ,  7516   b ,  7516   c , and  7516   d  such as lightings are high in luminance like  7513   a , and bright lines tend not to appear when captured by a receiver. Accordingly, a diffusion plate/prism  7516   e , a reflection plate  7516   f , a reflection plate/half mirror  7516   g , a reflection plate  7516   h , or a diffusion plate/prism  7516   j  is included to diffuse light, with it being possible to widen the part where bright lines appear. These transmitters are each captured with bright lines appearing in the periphery, like  7515   a . Since the receiver estimates the distance between the receiver and the transmitter using the size of the transmitter in the captured image, the part where light is diffused is set as the size of the light source and stored in a server or the like in association with the transmission ID, as a result of which the receiver can accurately estimate the distance to the transmitter. 
       FIG. 379  is a diagram illustrating an example of application of a transmitter in this embodiment. 
     A transmitter  7517   a  such as a lighting is high in luminance like  7513   a , and bright lines tend not to appear when captured by a receiver. Accordingly, a reflection plate  7517   b  is included to diffuse light, with it being possible to widen the part where bright lines appear. 
       FIG. 380  is a diagram illustrating an example of application of a transmitter in this embodiment. 
     A transmitter  7518   a  reflects light from a light source by a reflection plate  7518   c , as a result of which a receiver can capture bright lines in a wide range. A transmitter  7518   d  directs a light source toward a diffusion plate or prism  7518   e , as a result of which a receiver can capture bright lines in a wide range. 
       FIG. 381  is a diagram illustrating another example of operation of a receiver in this embodiment. 
     A receiver displays a bright line pattern using the above-mentioned synthetic image, intermediate image, or the like. Here, the receiver may be incapable of receiving a signal from a transmitter corresponding to the bright line pattern. When the user performs an operation (e.g. a tap) on the bright line pattern to select the bright line pattern, the receiver displays the synthetic image or intermediate image in which the bright line pattern is enlarged by optical zoom. Through such optical zoom, the receiver can appropriately receive the signal from the transmitter corresponding to the bright line pattern. That is, even when the captured image is too small to obtain the signal, the signal can be appropriately received by performing optical zoom. In the case where the displayed image is large enough to obtain the signal, too, faster reception is possible by optical zoom. 
     Summary of this Embodiment 
     An Information communication method in this embodiment is an information communication method of obtaining information from a subject, the information communication method including: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image by capturing the subject that changes in luminance by the image sensor with the set exposure time, the bright line image being an image including the bright line; displaying, based on the bright line image, a display image in which the subject and surroundings of the subject are shown, in a form that enables identification of a spatial position of a part where the bright line appears; and obtaining transmission information by demodulating data specified by a pattern of the bright line included in the obtained bright line image. 
     In this way, a synthetic image or an intermediate image illustrated in, for instance,  FIGS. 335 to 337 and 341  is displayed as the display image. In the display image in which the subject and the surroundings of the subject are shown, the spatial position of the part where the bright line appears is identified by a bright line pattern, a signal specification object, a signal identification object, a dotted frame, or the like. By looking at such a display image, the user can easily find the subject that is transmitting the signal through the change in luminance. 
     For example, the information communication method may further include: setting a longer exposure time than the exposure time; obtaining a normal captured image by capturing the subject and the surroundings of the subject by the image sensor with the longer exposure time; and generating a synthetic image by specifying, based on the bright line image, the part where the bright line appears in the normal captured image, and superimposing a signal object on the normal captured image, the signal object being an image indicating the part, wherein in the displaying, the synthetic image is displayed as the display image. 
     In this way, the signal object is, for example, a bright line pattern, a signal specification object, a signal identification object, a dotted frame, or the like, and the synthetic image is displayed as the display image as illustrated in  FIGS. 336, 337, and 341 . Hence, the user can more easily find the subject that is transmitting the signal through the change in luminance. 
     For example, in the setting of an exposure time, the exposure time may be set to 1/3000 second, in the obtaining of a bright line image, the bright line image in which the surroundings of the subject are shown may be obtained, and in the displaying, the bright line image may be displayed as the display image. 
     In this way, the bright line image is obtained and displayed as an intermediate image, for instance as illustrated in  FIG. 335 . This eliminates the need for a process of obtaining a normal captured image and a visible light communication image and synthesizing them, thus contributing to a simpler process. 
     For example, the image sensor may include a first image sensor and a second image sensor, in the obtaining of the normal captured image, the normal captured image may be obtained by image capture by the first image sensor, and in the obtaining of a bright line image, the bright line image may be obtained by image capture by the second image sensor simultaneously with the first image sensor. 
     In this way, the normal captured image and the visible light communication image which is the bright line image are obtained by the respective cameras, for instance as illustrated in  FIG. 337 . As compared with the case of obtaining the normal captured image and the visible light communication image by one camera, the images can be obtained promptly, contributing to a faster process. 
     For example, the information communication method may further include presenting, in the case where the part where the bright line appears is designated in the display image by an operation by a user, presentation information based on the transmission information obtained from the pattern of the bright line in the designated part. Examples of the operation by the user include: a tap; a swipe; an operation of continuously placing the user&#39;s fingertip on the part for a predetermined time or more; an operation of continuously directing the user&#39;s gaze to the part for a predetermined time or more; an operation of moving a part of the user&#39;s body according to an arrow displayed in association with the part; an operation of placing a pen tip that changes in luminance on the part; and an operation of pointing to the part with a pointer displayed in the display image by touching a touch sensor. 
     In this way, the presentation information is displayed as an information notification image, for instance as illustrated in  FIGS. 343 to 348 and 353 to 362 . Desired information can thus be presented to the user. 
     For example, the image sensor may be included in a head-mounted display, and in the displaying, the display image may be displayed by a projector included in the head-mounted display. 
     In this way, the information can be easily presented to the user, for instance as illustrated in  FIGS. 351 to 358 . 
     For example, an information communication method of obtaining information from a subject may include: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image by capturing the subject that changes in luminance by the image sensor with the set exposure time, the bright line image being an image including the bright line; and obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained bright line image, wherein in the obtaining of a bright line image, the bright line image including a plurality of parts where the bright line appears is obtained by capturing a plurality of subjects in a period during which the image sensor is being moved, and in the obtaining of the information, a position of each of the plurality of subjects is obtained by demodulating, for each of the plurality of parts, the data specified by the pattern of the bright line in the part, and the information communication method may further include estimating a position of the image sensor, based on the obtained position of each of the plurality of subjects and a moving state of the image sensor. 
     In this way, the position of the receiver including the image sensor can be accurately estimated based on the changes in luminance of the plurality of subjects such as lightings, for instance as illustrated in  FIG. 350 . 
     For example, an information communication method of obtaining information from a subject may include: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image by capturing the subject that changes in luminance by the image sensor with the set exposure time, the bright line image being an image including the bright line; obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained bright line image; and presenting the obtained information, wherein in the presenting, an image prompting to make a predetermined gesture is presented to a user of the image sensor as the information. 
     In this way, user authentication and the like can be conducted according to whether or not the user makes the gesture as prompted, for instance as illustrated in  FIGS. 363A to 364B . This enhances convenience. 
     For example, an information communication method of obtaining information from a subject may include: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image by capturing the subject that changes in luminance by the image sensor with the set exposure time, the bright line image being an image including the bright line; and obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained bright line image, wherein in the obtaining of a bright line image, the bright line image is obtained by capturing a plurality of subjects reflected on a reflection surface, and in the obtaining of the information, the information is obtained by separating a bright line corresponding to each of the plurality of subjects from bright lines included in the bright line image according to a strength of the bright line and demodulating, for each of the plurality of subjects, the data specified by the pattern of the bright line corresponding to the subject. 
     In this way, even in the case where the plurality of subjects such as lightings each change in luminance, appropriate information can be obtained from each subject, for instance as illustrated in  FIG. 370 . 
     For example, an information communication method of obtaining information from a subject may include: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image by capturing the subject that changes in luminance by the image sensor with the set exposure time, the bright line image being an image including the bright line; and obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained bright line image, wherein in the obtaining of a bright line image, the bright line image is obtained by capturing the subject reflected on a reflection surface, and the information communication method may further include estimating a position of the subject based on a luminance distribution in the bright line image. 
     In this way, the appropriate position of the subject can be estimated based on the luminance distribution, for instance as illustrated in  FIG. 371 . 
     For example, an information communication method of transmitting a signal using a change in luminance may include: determining a first pattern of the change in luminance, by modulating a first signal to be transmitted; determining a second pattern of the change in luminance, by modulating a second signal to be transmitted; and transmitting the first signal and the second signal by a light emitter alternately changing in luminance according to the determined first pattern and changing in luminance according to the determined second pattern. 
     In this way, the first signal and the second signal can each be transmitted without a delay, for instance as illustrated in  FIG. 365A . 
     For example, in the transmitting, a buffer time may be provided when switching the change in luminance between the change in luminance according to the first pattern and the change in luminance according to the second pattern. 
     In this way, interference between the first signal and the second signal can be suppressed, for instance as illustrated in  FIG. 365B . 
     For example, an information communication method of transmitting a signal using a change in luminance may include: determining a pattern of the change in luminance by modulating the signal to be transmitted; and transmitting the signal by a light emitter changing in luminance according to the determined pattern, wherein the signal is made up of a plurality of main blocks, each of the plurality of main blocks includes first data, a preamble for the first data, and a check signal for the first data, the first data is made up of a plurality of sub-blocks, and each of the plurality of sub-blocks includes second data, a preamble for the second data, and a check signal for the second data. 
     In this way, data can be appropriately obtained regardless of whether or not the receiver needs a blanking time, for instance as illustrated in  FIG. 366 . 
     For example, an information communication method of transmitting a signal using a change in luminance may include: determining, by each of a plurality of transmitters, a pattern of the change in luminance by modulating the signal to be transmitted; and transmitting, by each of the plurality of transmitters, the signal by a light emitter in the transmitter changing in luminance according to the determined pattern, wherein in the transmitting, the signal of a different frequency or protocol is transmitted. 
     In this way, interference between signals from the plurality of transmitters can be suppressed, for instance as illustrated in  FIG. 368 . 
     For example, an information communication method of transmitting a signal using a change in luminance may include: determining, by each of a plurality of transmitters, a pattern of the change in luminance by modulating the signal to be transmitted; and transmitting, by each of the plurality of transmitters, the signal by a light emitter in the transmitter changing in luminance according to the determined pattern, wherein in the transmitting, one of the plurality of transmitters receives a signal transmitted from an other one of the plurality of transmitters, and transmits an other signal in a form that does not interfere with the received signal. 
     In this way, interference between signals from the plurality of transmitters can be suppressed, for instance as illustrated in  FIG. 369 . 
     Embodiment 15 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as a blink pattern of an LED, an organic EL device, or the like in Embodiments 1 to 14 described above. 
       FIG. 382  is a flowchart illustrating an example of operation of a receiver in Embodiment 15. 
     First, a receiver receives a signal by an illuminance sensor (Step  8101 ). Next, the receiver obtains information such as position information from a server, based on the received signal (Step  8102 ). The receiver then activates an image sensor capable of capturing the light reception direction of the illuminance sensor (Step  8103 ). The receiver receives all or part of a signal by the image sensor, and determines whether or not all or part of the signal is the same as the signal received by the illuminance sensor (Step  8104 ). Following this, the receiver estimates the position of the receiver, from the position of the transmitter in the captured image, information from a 9-axis sensor included in the receiver, and the position information of the transmitter (Step  8105 ). Thus, the receiver activates the illuminance sensor of low power consumption and, in the case where the signal is received by the illuminance sensor, activates the image sensor. The receiver then performs position estimation using image capture by the image sensor. In this way, the position of the receiver can be accurately estimated while saving power. 
       FIG. 383  is a flowchart illustrating another example of operation of a receiver in Embodiment 15. 
     A receiver recognizes a periodic change of luminance from the sensor value of an illuminance sensor (Step  8111 ). The receiver then activates an image sensor capable of capturing the light reception direction of the illuminance sensor, and receives a signal (Step  8112 ). Thus, the receiver activates the illuminance sensor of low power consumption and, in the case where the periodic change of luminance is received by the illuminance sensor, activates the image sensor, in the same way as above. The receiver then receives the accurate signal using image capture by the image sensor. In this way, the accurate signal can be received while saving power. 
       FIG. 384A  is a block diagram illustrating an example of a transmitter in Embodiment 15. 
     A transmitter  8115  includes a power supply unit  8115   a , a signal control unit  8115   b , a light emitting unit  8115   c , and a light emitting unit  8115   d . The power supply unit  8115   a  supplies power to the signal control unit  8115   b . The signal control unit  8115   b  divides the power supplied from the power supply unit  8115   a  into the light emitting units  8115   c  and  8115   d , and controls the luminance changes of the light emitting units  8115   c  and  8115   d.    
       FIG. 384B  is a block diagram illustrating another example of a transmitter in Embodiment 15. 
     A transmitter  8116  includes a power supply unit  8116   a , a signal control unit  8116   b , a light emitting unit  8116   c , and a light emitting unit  8116   d . The power supply unit  8116   a  supplies power to the light emitting units  8116   c  and  8116   d . The signal control unit  8116   b  controls the power supplied from the power supply unit  8116   a , thereby controlling the luminance changes of the light emitting units  8116   c  and  8116   d . The power use efficiency can be enhanced by the signal control unit  8116   b  controlling the power supply unit  8116   a  that supplies power to each of the light emitting units  8116   c  and  8116   d.    
       FIG. 385  is a diagram illustrating an example of a structure of a system including a plurality of transmitters in Embodiment 15. 
     The system includes a centralized control unit  8118 , a transmitter  8117 , and a transmitter  8120 . The centralized control unit  8118  controls signal transmission by a change in luminance of each of the transmitters  8117  and  8120 . For example, the centralized control unit  8118  causes the transmitters  8117  and  8120  to transmit the same signal at the same time, or causes one of the transmitters to transmit a signal unique to the transmitter. 
     The transmitter  8120  includes two transmission units  8121  and  8122 , a signal change unit  8123 , a signal storage unit  8124 , a synchronous signal input unit  8125 , a synchronous control unit  8126 , and a light receiving unit  8127 . 
     The two transmission units  8121  and  8122  each have the same structure as the transmitter  8115  illustrated in  FIG. 384A , and transmits a signal by changing in luminance. In detail, the transmission unit  8121  includes a power supply unit  8121   a , a signal control unit  8121   b , a light emitting unit  8121   c , and a light emitting unit  8121   d . The transmission unit  8122  includes a power supply unit  8122   a , a signal control unit  8122   b , a light emitting unit  8122   c , and a light emitting unit  8122   d.    
     The signal change unit  8123  modulates a signal to be transmitted, to a signal indicating a luminance change pattern. The signal storage unit  8124  stores the signal indicating the luminance change pattern. The signal control unit  8121   b  in the transmission unit  121  reads the signal stored in the signal storage unit  8124 , and causes the light emitting units  8121   c  and  8121   d  to change in luminance according to the signal. 
     The synchronous signal input unit  8125  obtains a synchronous signal according to control by the centralized control unit  8118 . The synchronous control unit  8126  synchronizes the luminance changes of the transmission units  8121  and  8122 , when the synchronous signal is obtained. That is, the synchronous control unit  8126  controls the signal control units  8121   b  and  8122   b , to synchronize the luminance changes of the transmission units  8121  and  8122 . Here, the light receiving unit  8127  detects light emission from the transmission units  8121  and  8122 . The synchronous control unit  8126  feedback-controls the signal control units  8121   b  and  8122   b , according to the light detected by the light receiving unit  8127 . 
       FIG. 386  is a block diagram illustrating another example of a transmitter in Embodiment 15. 
     A transmitter  8130  includes a transmission unit  8131  that transmits a signal by changing in luminance, and a non-transmission unit  8132  that emits light without transmitting a signal. 
     The transmission unit  8131  has the same structure as the transmitter  8115  illustrated in  FIG. 384A , and includes a power supply unit  8131   a , a signal control unit  8131   b , and light emitting units  8131   c  to  8131   f . The non-transmission unit  8132  includes a power supply unit  8132   a  and light emitting units  8132   c  to  8132   f , but does not include a signal control unit. In other words, in the case where there are a plurality of units each including a power supply and luminance change synchronous control cannot be performed between the plurality of units, a signal control unit is provided in only one of the plurality of units to cause the unit to change in luminance, as in the structure illustrated in  FIG. 386 . 
     In the transmitter  8130 , the light emitting units  8131   c  to  8131   f  in the transmission unit  8131  are continuously arranged in a line. That is, none of the light emitting units  8132   c  to  8132   f  in the non-transmission unit  8132  is mixed in the set of the light emitting units  8131   c  to  8131   f . This makes the light emitter that changes in luminance larger in size, so that the receiver can easily receive the signal transmitted using the change in luminance. 
       FIG. 387A  is a diagram illustrating an example of a transmitter in Embodiment 15. 
     A transmitter  8134  such as a signage includes three light emitting units (light emitting areas)  8134   a  to  8134   c . Light from these light emitting units  8134   a  to  8134   c  do not interfere with each other. In the case where only one of the light emitting units  8134   a  to  8134   c  can be changed in luminance to transmit a signal, it is desirable to change in luminance the light emitting unit  8134   b  at the center, as illustrated in (a) in  FIG. 387A . In the case where two of the light emitting units  8134   a  to  8134   c  can be changed in luminance, it is desirable to change in luminance the light emitting unit  8134   b  at the center and the light emitting unit  8134   a  or  8134   c  at either edge, as illustrated in (b) in  FIG. 387A . Changing in luminance the light emitting units at such positions enables the receiver to appropriately receive the signal transmitted using the change in luminance. 
       FIG. 387B  is a diagram illustrating an example of a transmitter in Embodiment 15. 
     A transmitter  8135  such as a signage includes three light emitting units  8135   a  to  8135   c . Light from adjacent light emitting units of these light emitting units  8135   a  to  8135   c  interferes with each other. In the case where only one of the light emitting units  8135   a  to  8135   c  can be changed in luminance to transmit a signal, it is desirable to change in luminance the light emitting unit  8135   a  or  8135   c  at either edge, as illustrated in (a) in  FIG. 387B . This prevents light from another light emitting unit from interfering with the luminance change for signal transmission. In the case where two of the light emitting units  8135   a  to  8135   c  can be changed in luminance, it is desirable to change in luminance the light emitting unit  8135   b  at the center and the light emitting unit  8135   a  or  8135   c  at either edge, as illustrated in (b) in  FIG. 387B . Changing in luminance the light emitting units at such positions contributes to a larger luminance change area, and so enables the receiver to appropriately receive the signal transmitted using the change in luminance. 
       FIG. 387C  is a diagram illustrating an example of a transmitter in Embodiment 15. 
     In the case where two of the light emitting units  8134   a  to  8134   c  can be changed in luminance in the transmitter  8134 , the light emitting units  8134   a  and  8134   c  at both edges may be changed in luminance, as illustrated in  FIG. 378C . In this case, the imaging range in which the luminance change part is shown can be widened in the image capture by the receiver. 
       FIG. 388A  is a diagram illustrating an example of a transmitter in Embodiment 15. 
     A transmitter  8137  such as a signage transmits a signal by a character part “A Shop” and a light emitting unit  8137   a  changing in luminance. For example, the light emitting unit  8137   a  is formed like a horizontally long rectangle, and uniformly changes in luminance. The uniform change in luminance of the light emitting unit  8137   a  enables the receiver to appropriately receive the signal transmitted using the change in luminance. 
       FIG. 388B  is a diagram illustrating an example of a transmitter in Embodiment 15. 
     A transmitter  8138  such as a signage transmits a signal by a character part “A Shop” and a light emitting unit  8138   a  changing in luminance. For example, the light emitting unit  8138   a  is formed like a frame along the edges of the signage, and uniformly changes in luminance. That is, the light emitting unit  8138   a  is formed so that, when the light emitting unit is projected onto an arbitrary straight line, the length of the continuous projection part is at the maximum. The uniform change in luminance of the light emitting unit  8138   a  enables the receiver to more appropriately receive the signal transmitted using the change in luminance. 
       FIG. 389  is a diagram illustrating an example of processing operation of a receiver, a transmitter, and a server in Embodiment 15. 
     A receiver  8142  such as a smartphone obtains position information indicating the position of the receiver  8142 , and transmits the position information to a server  8141 . For example, the receiver  8142  obtains the position information when using a GPS or the like or receiving another signal. The server  8141  transmits an ID list associated with the position indicated by the position information, to the receiver  8142 . The ID list includes each ID such as “abcd” and information associated with the ID. 
     The receiver  8142  receives a signal from a transmitter  8143  such as a lighting device. Here, the receiver  8142  may be able to receive only a part (e.g. “b”) of an ID as the above-mentioned signal. In such a case, the receiver  8142  searches the ID list for the ID including the part. In the case where the unique ID is not found, the receiver  8142  further receives a signal including another part of the ID, from the transmitter  8143 . The receiver  8142  thus obtains a larger part (e.g. “bc”) of the ID. The receiver  8142  again searches the ID list for the ID including the part (e.g. “bc”). Through such search, the receiver  8142  can specify the whole ID even in the case where the ID can be obtained only partially. Note that, when receiving the signal from the transmitter  8143 , the receiver  8142  receives not only the part of the ID but also a check portion such as a CRC (Cyclic Redundancy Check). 
       FIG. 390  is a diagram illustrating an example of processing operation of a receiver, a transmitter, and a server in Embodiment 15. 
     A receiver  8152  such as a smartphone obtains position information indicating the position of the receiver  8152 . For example, the receiver  8152  obtains the position information when using a GPS or the like or receiving another signal. The receiver  8152  also receives a signal from a transmitter  8153  such as a lighting device. The signal includes only a part (e.g. “b”) of an ID. The receiver  8152  transmits the position information and the part of the ID to a server  8151 . 
     The server  8151  searches an ID list associated with the position indicated by the position information, for the ID including the part. In the case where the unique ID is not found, the server  8151  notifies the receiver  8152  that the specification of the ID has failed. 
     Following this, the receiver  8152  receives a signal including another part of the ID, from the transmitter  8153 . The receiver  8152  thus obtains a large part (e.g. “be”) of the ID. The receiver  8152  transmits the part (e.g. “be”) of the ID and the position information to the server  8151 . 
     The server  8151  searches the ID list associated with the position indicated by the position information, for the ID including the part. When the unique ID is found, the server  8151  notifies the receiver  8152  that the ID (e.g. “abef”) has been specified, and transmits information associated with the ID to the receiver  8152 . 
       FIG. 391  is a diagram illustrating an example of processing operation of a receiver, a transmitter, and a server in Embodiment 15. 
     The receiver  8152  may transmit not the part of the ID but the whole ID to the server  8151 , together with the position information. In the case where the complete ID (e.g. “wxyz”) is not included in the ID list, the server  8151  notifies the receiver  8152  of an error. 
       FIG. 392A  is a diagram for describing synchronization between a plurality of transmitters in Embodiment 15. 
     Transmitters  8155   a  and  8155   b  transmit a signal by changing in luminance. Here, the transmitter  8155   a  transmits a synchronous signal to the transmitter  8155   b , thereby changing in luminance synchronously with the transmitter  8155   b . Further, the transmitters  8155   a  and  8155   b  each obtain a signal from a source, and change in luminance according to the signal. There is a possibility that the time (first delay time) taken for the signal transmission from the source to the transmitter  8155   a  and the time (second delay time) taken for the signal transmission from the source to the transmitter  8155   b  are different. In view of this, the signal round-trip time between each of the transmitters  8155   a  and  8155   b  and the source is measured, and ½ of the round-trip time is specified as the first or second delay time. The transmitter  8155   a  transmits the synchronous signal so as to cancel out the difference between the first and second delay times, thereby changing in luminance synchronously with the transmitter  8155   b.    
       FIG. 392B  is a diagram for describing synchronization between a plurality of transmitters in Embodiment 15. 
     A light receiving sensor  8156  detects light from the transmitters  8155   a  and  8155   b , and outputs the result to the transmitters  8155   a  and  8155   b  as a detection signal. Having received the detection signal from the light receiving sensor  8156 , the transmitters  8155   a  and  8155   b  change in luminance synchronously or adjust the signal strength based on the detection signal. 
       FIG. 393  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     A transmitter  8165  such as a television obtains an image and an ID (ID  1000 ) associated with the image, from a control unit  8166 . The transmitter  8165  displays the image, and also transmits the ID (ID  1000 ) to a receiver  8167  by changing in luminance. The receiver  8167  captures the transmitter  8165  to receive the ID (ID  1000 ), and displays information associated with the ID (ID  1000 ). The control unit  8166  then changes the image output to the transmitter  8165 , to another image. The control unit  8166  also changes the ID output to the transmitter  8165 . That is, the control unit  8166  outputs the other image and the other ID (ID  1001 ) associated with the other image, to the transmitter  8165 . The transmitter  8165  displays the other image, and transmits the other ID (ID  1001 ) to the receiver  8167  by changing in luminance. The receiver  8167  captures the transmitter  8165  to receive the other ID (ID  1001 ), and displays information associated with the other ID (ID  1001 ). 
       FIG. 394  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     A transmitter  8170  such as a signage displays images by switching between them. When displaying an image, the transmitter  8170  transmits, to a receiver  8171 , ID time information indicating the ID corresponding to the displayed image and the time at which the image is displayed, by changing in luminance. For example, at time t 1 , the transmitter  8170  displays an image showing a circle, and transmits ID time information indicating the ID (ID:  1000 ) corresponding to the image and the time (TIME: t 1 ) at which the image is displayed. 
     Here, the transmitter  8170  transmits not only the ID time information corresponding to the currently displayed image but also ID time information corresponding to at least one previously displayed image. For example, at time t 2 , the transmitter  8170  displays an image showing a square, and transmits ID time information indicating the ID (ID:  1001 ) corresponding to the image and the time (TIME: t 2 ) at which the image is displayed. At this time, the transmitter  8170  also transmits the ID time information indicating the ID (ID:  1000 ) corresponding to the image showing the circle and the time (TIME: t 1 ) at which the image is displayed. Likewise, at time t 3 , the transmitter  8170  displays an image showing a triangle, and transmits ID time information indicating the ID (ID:  1002 ) corresponding to the image and the time (TIME: t 3 ) at which the image is displayed. At this time, the transmitter  8170  also transmits the ID time information indicating the ID (ID:  1001 ) corresponding to the image showing the square and the time (TIME: t 2 ) at which the image is displayed. Thus, the transmitter  8170  transmits a plurality of sets of ID time information at the same time. 
     Suppose, to obtain information related to the image showing the square, the user points an image sensor of the receiver  8171  at the transmitter  8170  and starts image capture by the receiver  8171 , at the time t 2  at which the image showing the square is displayed. 
     Even when the receiver  8171  starts capturing at time t 2 , the receiver  8171  may not be able to obtain the ID time information corresponding to the image showing the square while the image is displayed on the transmitter  8170 . Even in such a case, since the ID time information corresponding to the previously displayed image is also transmitted from the transmitter  8170  as mentioned above, at time t 3  the receiver  8171  can obtain not only the ID time information (ID:  1002 , TIME: t 3 ) corresponding to the image showing the triangle but also the ID time information (ID:  1001 , TIME: t 2 ) corresponding to the image showing the square. The receiver  8171  selects, from these ID time information, the ID time information (ID:  1001 , TIME: t 2 ) indicating the time (t 2 ) at which the receiver  8171  is pointed at the transmitter  8170 , and specifies the ID (ID:  1001 ) indicated by the ID time information. As a result, at time t 3 , the receiver  8171  can obtain, from a server or the like, information related to the image showing the square based on the specified ID (ID:  1001 ). 
     The above-mentioned time is not limited to an absolute time, and may be a time (relative time) between the time at which the receiver  8171  is pointed at the transmitter  8170  and the time at which the receiver  8171  receives the ID time information. Moreover, though the transmitter  8170  transmits the ID time information corresponding to the previously displayed image together with the ID time information corresponding to the currently displayed image, the transmitter  8170  may transmit ID time information corresponding to an image to be displayed in the future. Furthermore, in a situation where the reception by the receiver  8171  is difficult, the transmitter  8170  may transmit more sets of previous or future ID time information. 
     In the case where the transmitter  8170  is not a signage but a television, the transmitter  8170  may transmit information indicating a channel corresponding to a displayed image, instead of ID time information. In detail, in the case where an image of a television program being broadcasted is displayed on the transmitter  8170  in real time, the display time of the image displayed on the transmitter  8170  can be uniquely specified for each channel. Accordingly, the receiver  8171  can specify the time at which the receiver  8171  is pointed at the transmitter  8170 , i.e. the time at which the receiver  8171  starts capturing, based on the captured image and the channel. The receiver  8171  can then obtain, from a server or the like, information related to the captured image based on the channel and the time. Here, the transmitter  8170  may transmit information indicating the display time of the displayed image, instead of ID time information. In such a case, the receiver  8171  searches all television programs being broadcasted, for a television program including the captured image. The receiver  8171  can then obtain, from a server or the like, information related to the image based on the channel and display time of the television program. 
       FIG. 395  is a diagram illustrating an example of operation of a transmitter, a receiver, and a server in Embodiment 15. 
     As illustrated in (a) in  FIG. 395 , a receiver  8176  captures a transmitter  8175  to obtain an image including a bright line, and specifies (obtains) the ID of the transmitter  8175  from the image. The receiver  8176  transmits the ID to a server  8177 , and obtains information associated with the ID from the server  8177 . 
     On the other hand, as illustrated in (b) in  FIG. 395 , the receiver  8176  may capture the transmitter  8175  to obtain the image including the bright line, and transmit the image to the server  8177  as captured data. The receiver  8176  may also perform, on the image including the bright line, such preprocessing that reduces the amount of information of the image, and transmit the preprocessed image to the server  8177  as captured data. The preprocessing is, for instance, image binarization. Having received the captured data, the server  8177  specifies (obtains) the ID of the transmitter  8175  from the image indicated by the captured data. The server  8177  then transmits the information associated with the ID to the receiver  8176 . 
       FIG. 396  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     When the user is located at position A, a receiver  8183  specifies the position of the receiver  8183 , by obtaining a signal transmitted from a transmitter  8181  that changes in luminance. The receiver  8183  displays a point  8183   b  indicating the specified position, together with an error range  8183   a  of the position. 
     Next, when the user moves from position A to position B, the receiver  8183  cannot obtain a signal from the transmitter  8181 . The receiver  8183  accordingly estimates the position of the receiver  8183 , using a 9-axis sensor and the like included in the receiver  8183 . The receiver  8183  displays the point  8183   b  indicating the estimated position, together with the error range  8183   a  of the position. Since this position is estimated by the 9-axis sensor, a larger error range  8183   a  is displayed. 
     Next, when the user moves from position B to position C, the receiver  8183  specifies the position of the receiver  8183 , by obtaining a signal transmitted from another transmitter  8182  that changes in luminance. The receiver  8183  displays the point  8183   b  indicating the specified position, together with the error range  8183   a  of the position. Here, the receiver  8183  does not instantly switch the display from the point  8183   b  indicating the position estimated using the 9-axis sensor and its error range  8183   a  to the position specified as mentioned above and its error range, but smoothly switches the display with movement. The error range  8183   a  becomes smaller as a result. 
       FIG. 397  is a diagram illustrating an example of appearance of a receiver in Embodiment 15. 
     The receiver  8183  such as a smartphone (advanced mobile phone) includes an image sensor  8183   c , an illuminance sensor  8183   d , and a display  8183   e  on its front surface, as illustrated in (a) in  FIG. 397 . The image sensor  8183   c  obtains an image including a bright line by capturing a subject that changes in luminance as mentioned above. The illuminance sensor  8183   d  detects the change in luminance of the subject. Hence, the illuminance sensor  8183   d  can be used in place of the image sensor  8183   c , depending on the state or situation of the subject. The display  8183   e  displays an image and the like. The receiver  8183  may also have a function as a subject that changes in luminance. In this case, the receiver  8183  transmits a signal by causing the display  8183   e  to change in luminance. 
     The receiver  8183  also includes an image sensor  8183   f , an illuminance sensor  8183   g , and a flash light emitting unit  8183   h  on its back surface, as illustrated in (b) in  FIG. 397 . The image sensor  8183   f  is the same as the above-mentioned image sensor  8183   c , and obtains an image including a bright line by capturing a subject that changes in luminance as mentioned above. The illuminance sensor  8183   g  is the same as the above-mentioned illuminance sensor  8183   d , and detects the change in luminance of the subject. Hence, the illuminance sensor  8183   g  can be used in place of the image sensor  8183   f , depending on the state or situation of the subject. The flash light emitting unit  8183   h  emits flash for imaging. The receiver  8183  may also have a function as a subject that changes in luminance. In this case, the receiver  8183  transmits a signal by causing the flash light emitting unit  8183   h  to change in luminance. 
       FIG. 398  is a diagram illustrating an example of operation of a transmitter, a receiver, and a server in Embodiment 15. 
     A transmitter  8185  such as a smartphone transmits information indicating “Coupon 100 yen off” as an example, by causing a part of a display  8185   a  except a barcode part  8185   b  to change in luminance, i.e. by visible light communication. The transmitter  8185  also causes the barcode part  8185   b  to display a barcode without changing in luminance. The barcode indicates the same information as the above-mentioned information transmitted by visible light communication. The transmitter  8185  further causes the part of the display  8185   a  except the barcode part  8185   b  to display the characters or pictures, e.g. the characters “Coupon 100 yen off”, indicating the information transmitted by visible light communication. Displaying such characters or pictures allows the user of the transmitter  8185  to easily recognize what kind of information is being transmitted. 
     A receiver  8186  performs image capture to obtain the information transmitted by visible light communication and the information indicated by the barcode, and transmits these information to a server  8187 . The server  8187  determines whether or not these information match or relate to each other. In the case of determining that these information match or relate to each other, the server  8187  executes a process according to these information. Alternatively, the server  8187  transmits the determination result to the receiver  8186  so that the receiver  8186  executes the process according to these information. 
     The transmitter  8185  may transmit a part of the information indicated by the barcode, by visible light communication. Moreover, the URL of the server  8187  may be indicated in the barcode. Furthermore, the transmitter  8185  may obtain an ID as a receiver, and transmit the ID to the server  8187  to thereby obtain information associated with the ID. The information associated with the ID is the same as the information transmitted by visible light communication or the information indicated by the barcode. The server  8187  may transmit an ID associated with information (visible light communication information or barcode information) transmitted from the transmitter  8185  via the receiver  8186 , to the transmitter  8185 . 
       FIG. 399  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     The transmitter  8185  such as a smartphone transmits a signal by causing the display  8185   a  to change in luminance. A receiver  8188  includes a light-resistant cone-shaped container  8188   b  and an illuminance sensor  8188   a . The illuminance sensor  8188   a  is contained in the container  8188   b , and located near the tip of the container  8188   b . When the signal is transmitted from the transmitter  8185  by visible light communication, the opening (bottom) of the container  8188   b  in the receiver  8188  is directed to the display  8185   a . Since no light other than the light from the display  8185   a  enters the container  8188   b , the illuminance sensor  8188   a  in the receiver  8188  can appropriately receive the light from the display  8185   a  without being affected by any light which is noise. As a result, the receiver  8188  can appropriately receive the signal from the transmitter  8185 . 
       FIG. 400  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     A transmitter  8190  such as a bus stop sign transmits operation information indicating a bus operation state and the like to the receiver  8183 , by changing in luminance. For instance, the operation information indicating the destination of a bus, the arrival time of the bus at the bus stop, the current position of the bus, and the like is transmitted to the receiver  8183 . Having received the operation information, the receiver  8183  displays the contents of the operation information on its display. 
     For example, suppose buses with different destinations stop at the bus stop. The transmitter  8190  transmits operation information about these buses with the different destinations. Having received these operation information, the receiver  8183  selects operation information of a bus with a destination that is frequently used by the user, and displays the contents of the selected operation information on the display. In detail, the receiver  8183  specifies the destination of each bus used by the user through a GPS or the like, and records a history of destinations. With reference to this history, the receiver  8183  selects operation information of a bus with a destination frequently used by the user. As an alternative, the receiver  8183  may display the contents of operation information selected by the user from these operation information, on the display. As another alternative, the receiver  8183  may display, with priority, operation information of a bus with a destination frequently selected by the user. 
       FIG. 401  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     A transmitter  8191  such as a signage transmits information of a plurality of shops to the receiver  8183 , by changing in luminance. This information summarizes information about the plurality of shops, and is not information unique to each shop. Accordingly, having received the information by image capture, the receiver  8183  can display information about not only one shop but the plurality of shops. The receiver  8183  selects information about a shop (e.g. “B shop”) within the imaging range from the information about the plurality of shops, and displays the selected information. When displaying the information, the receiver  8183  translates the language for expressing the information to a language registered beforehand, and displays the information in the translated language. Moreover, a message prompting for image capture by an image sensor (camera) of the receiver  8183  may be displayed on the transmitter  8191  using characters or the like. In detail, a special application program is started to display, on the transmitter  8191 , a message (e.g. “Get information with camera”) informing that information can be provided if the transmitter  8191  is captured by camera. 
       FIG. 402  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 15. 
     For example, the receiver  8183  captures a subject including a plurality of persons  8197  and a street lighting  8195 . The street lighting  8195  includes a transmitter  8195   a  that transmits information by changing in luminance. By capturing the subject, the receiver  8183  obtains an image in which the image of the transmitter  8195   a  appears as the above-mentioned bright line pattern. The receiver  8183  obtains an AR object  8196   a  associated with an ID indicated by the bright line pattern, from a server or the like. The receiver  8183  superimposes the AR object  8196   a  on a normal captured image  8196  obtained by normal imaging, and displays the normal captured image  8196  on which the AR object  8196   a  is superimposed. 
       FIG. 403A  is a diagram illustrating an example of a structure of information transmitted by a transmitter in Embodiment 15. 
     For example, information transmitted by a transmitter is made up of a preamble unit, a data unit of fixed length, and a check unit. A receiver checks the data unit using the check unit, thus successfully receiving the information made up of these units. When the receiver receives the preamble unit and the data unit but cannot receive the check unit, the receiver omits the check using the check unit. Even in such a case where the check is omitted, the receiver can successfully receive the information made up of these units. 
       FIG. 403B  is a diagram illustrating another example of a structure of information transmitted by a transmitter in Embodiment 15. 
     For example, information transmitted by a transmitter is made up of a preamble unit, a check unit, and a data unit of variable length. The next information transmitted by the transmitter is equally made up of the preamble unit, the check unit, and the data unit of variable length. When a receiver receives one preamble unit and the next preamble unit, the receiver recognizes information from the preamble unit to immediately before the next preamble unit, as one set of significant information. The receiver may also use the check unit, to specify the end of the data unit received following the check unit. In this case, even when the receiver cannot receive the above-mentioned next preamble unit (all or part of the preamble unit), the receiver can appropriately receive one set of significant information transmitted immediately before. 
       FIG. 404  is a diagram illustrating an example of a 4-value PPM modulation scheme by a transmitter in Embodiment 15. 
     A transmitter modulates a transmission signal (signal to be transmitted) to a luminance change pattern by a 4-value PPM modulation scheme. When doing so, the transmitter can maintain the brightness of light that changes in luminance constant, regardless of the transmission signal. 
     For instance, in the case of maintaining the brightness at 75%, the transmitter modulates each of the transmission signals “00”, “01”, “10”, and “11” to a luminance change pattern in which luminance L (Low) is represented in one of four consecutive slots and luminance H (High) is represented in the other three slots. In detail, the transmitter modulates the transmission signal “00” to a luminance change pattern (L, H, H, H) in which luminance L is represented in the first slot and luminance H is represented in the second to fourth slots. In this luminance change, the luminance rises between the first and second slots. Likewise, the transmitter modulates the transmission signal “01” to a luminance change pattern (H, L, H, H) in which luminance L is represented in the second slot and luminance H is represented in the first, third, and fourth slots. In this luminance change, the luminance rises between the second and third slots. 
     In the case of maintaining the brightness at 50%, the transmitter modulates each of the transmission signals “00”, “01”, “10”, and “11” to a luminance change pattern in which luminance L (Low) is represented in two of the four slots and luminance H (High) is represented in the other two slots. In detail, the transmitter modulates the transmission signal “00” to a luminance change pattern (L, H, H, L) in which luminance L is represented in the first and fourth slots and luminance H is represented in the second and third slots. In this luminance change, the luminance rises between the first and second slots. Likewise, the transmitter modulates the transmission signal “01” to a luminance change pattern (L, L, H, H) in which luminance L is represented in the first and second slots and luminance H is represented in the third and fourth slots. Alternatively, the transmitter modulates the transmission signal “01” to a luminance change pattern (H, L, H, L) in which luminance L is represented in the second and fourth slots and luminance H is represented in the first and third slots. In this luminance change, the luminance rises between the second and third slots. 
     In the case of maintaining the brightness at 25%, the transmitter modulates each of the transmission signals “00”, “01”, “10”, and “11” to a luminance change pattern in which luminance L (Low) is represented in three of the four slots and luminance H (High) is represented in the other slot. In detail, the transmitter modulates the transmission signal “00” to a luminance change pattern (L, H, L, L) in which luminance L is represented in the first, third, and fourth slots and luminance H is represented in the second slot. In this luminance change, the luminance rises between the first and second slots. Likewise, the transmitter modulates the transmission signal “01” to a luminance change pattern (L, L, H, L) in which luminance L is represented in the first, second, and fourth slots and luminance H is represented in the third slot. In this luminance change, the luminance rises between the second and third slots. 
     By the above-mentioned 4-value PPM modulation scheme, the transmitter can suppress flicker, and also easily adjust the brightness in levels. Moreover, a receiver can appropriately demodulate the luminance change pattern by specifying the position at which the luminance rises. Here, the receiver does not use but ignores whether or not the luminance rises at the boundary between one slot group made up of four slots and the next slot group, when demodulating the luminance change pattern. 
       FIG. 405  is a diagram illustrating an example of a PPM modulation scheme by a transmitter in Embodiment 15. 
     A transmitter modulates a transmission signal to a luminance change pattern, as in the 4-value PPM modulation scheme illustrated in  FIG. 404 . Here, the transmitter may perform PPM modulation without switching the luminance between L and H per slot. In detail, the transmitter performs PPM modulation by switching the position at which the luminance rises in the duration (time width) (hereafter referred to as “unit duration”) of four consecutive slots illustrated in  FIG. 404 , depending on the transmission signal. For example, the transmitter modulates the transmission signal “00” to a luminance change pattern in which the luminance rises at the position of 25% in the unit duration, as illustrated in  FIG. 405 . Likewise, the transmitter modulates the transmission signal “01” to a luminance change pattern in which the luminance rises at the position of 50% of the unit duration, as illustrated in  FIG. 405 . 
     In the case of maintaining the brightness at 75%, the transmitter modulates the transmission signal “00” to a luminance change pattern in which luminance L is represented in the position of 0 to 25% and luminance H is represented in the position of 25 to 100% in the unit duration. In the case of maintaining the brightness at 99%, the transmitter modulates the transmission signal “00” to a luminance change pattern in which luminance L is represented in the position of 24 to 25% and luminance H is represented in the position of 0 to 24% and the position of 25 to 100% in the unit duration. Likewise, in the case of maintaining the brightness at 1%, the transmitter modulates the transmission signal “00” to a luminance change pattern in which luminance L is represented in the position of 0 to 25% and the position of 26 to 100% and luminance H is represented in the position of 25 to 26% in the unit duration. 
     By such switching the luminance between L and H at an arbitrary position in the unit duration without switching the luminance between L and H per slot, it is possible to adjust the brightness continuously. 
       FIG. 406  is a diagram illustrating an example of a PPM modulation scheme by a transmitter in Embodiment 15. 
     A transmitter performs modulation in the same way as in the PPM modulation scheme illustrated in  FIG. 405 . Here, regardless of the transmission signal, the transmitter modulates the signal to a luminance change pattern in which luminance H is represented at the start of the unit duration and luminance L is represented at the end of the unit duration. Since the luminance rises at the boundary between one unit duration and the next unit duration, a receiver can appropriately specify the boundary. Therefore, the receiver and the transmitter can correct clock discrepancies. 
       FIG. 407A  is a diagram illustrating an example of a luminance change pattern corresponding to a header (preamble unit) in Embodiment 15. 
     For example, in the case of transmitting the header (preamble unit) illustrated in  FIGS. 403A and 403B , a transmitter changes in luminance according to a pattern illustrated in  FIG. 407A . In detail, in the case where the header is made up of 7 slots, the transmitter changes in luminance according to the pattern “L, H, L, H, L, H, H”. In the case where the header is made up of 8 slots, the transmitter changes in luminance according to the pattern “H, L, H, L, H, L, H, H”. These patterns are distinguishable from the luminance change patterns illustrated in  FIG. 404 , with it being possible to clearly inform a receiver that the signal indicated by any of these patterns is the header. 
       FIG. 407B  is a diagram illustrating an example of a luminance change pattern in Embodiment 15. 
     In the 4-value PPM modulation scheme, in the case of modulating the transmission signal “01” Included in the data unit while maintaining the brightness at 50%, the transmitter modulates the signal to one of the two patterns, as illustrated in  FIG. 404 . In detail, the transmitter modulates the signal to the first pattern “L, L, H, H” or the second pattern “H, L, H, L”. 
     Here, suppose the luminance change pattern corresponding to the header is such a pattern as illustrated in  FIG. 407A . In this case, it is desirable that the transmitter modulates the transmission signal “01” to the first pattern “L, L, H, H”. For instance, in the case of using the first pattern, the transmission signal “11, 01, 11” included in the data unit is modulated to the pattern “H, H, L, L, L, L, H, H, H, H, L, L”. In the case of using the second pattern, on the other hand, the transmission signal “11, 01, 11” included in the data unit is modulated to the pattern “H, H, L, L, H, L, H, L, H, H, L, L”. The pattern “H, H, L, L, H, L, H, L, H, H, L, L” includes the same pattern as the pattern of the header made up of 7 slots illustrated in  FIG. 407A . For clear distinction between the header and the data unit, it is desirable to modulate the transmission signal “01” to the first pattern. 
       FIG. 408A  is a diagram illustrating an example of a luminance change pattern in Embodiment 15. 
     In the 4-value PPM modulation scheme, in the case of modulating the transmission signal “11”, the transmitter modulates the signal to the pattern “H, H, H, L”, the pattern “H, H, L, L”, or the pattern “H, L, L, L” so as not to cause a rise in luminance, as illustrated in  FIG. 404 . However, the transmitter may modulate the transmission signal “11” to the pattern “H, H, H, H” or the pattern “L, L, L, L” in order to adjust the brightness, as illustrated in  FIG. 408A . 
       FIG. 408B  is a diagram illustrating an example of a luminance change pattern in Embodiment 15. 
     In the 4-value PPM modulation scheme, in the case of modulating the transmission signal “11, 00” while maintaining the brightness at 75%, the transmitter modulates the signal to the pattern “H, H, H, L, L, H, H, H”, as illustrated in  FIG. 404 . However, if luminance L is consecutive, each of the consecutive values of luminance L other than the last value may be changed to H so that luminance L is not consecutive. That is, the transmitter modulates the signal “11, 00” to the pattern “H, H, H, H, L, H, H, H”. 
     Since luminance L is not consecutive, the load on the transmitter can be reduced. Moreover, the capacitance of the capacitor included in the transmitter can be reduced, enabling a reduction in control circuit capacity. Furthermore, a lighter load on the light source of the transmitter facilitates the production of the light source. The power efficiency of the transmitter can also be enhanced. Besides, since it is ensured that luminance L is not consecutive, the receiver can easily demodulate the luminance change pattern. 
     Summary of this Embodiment 
     An information communication method in this embodiment is an information communication method of transmitting a signal using a change in luminance, the information communication method including: determining a pattern of the change in luminance by modulating the signal to be transmitted; and transmitting the signal by a light emitter changing in luminance according to the determined pattern, wherein the pattern of the change in luminance is a pattern in which one of two different luminance values occurs in each arbitrary position in a predetermined duration, and in the determining, the pattern of the change in luminance is determined so that, for each of different signals to be transmitted, a luminance change position in the duration is different and an integral of luminance of the light emitter in the duration is a same value corresponding to preset brightness, the luminance change position being a position at which the luminance rises or a position at which the luminance falls. 
     In this way, the luminance change pattern is determined so that, for each of the different signals “00”, “01”, “10”, and “11” to be transmitted, the position at which the luminance rises (luminance change position) is different and also the integral of luminance of the light emitter in the predetermined duration (unit duration) is the same value corresponding to the preset brightness (e.g. 99% or 1%), for instance as illustrated in  FIG. 405 . Thus, the brightness of the light emitter can be maintained constant for each signal to be transmitted, with it being possible to suppress flicker. In addition, a receiver that captures the light emitter can appropriately demodulate the luminance change pattern based on the luminance change position. Furthermore, since the luminance change pattern is a pattern in which one of two different luminance values (luminance H (High) or luminance L (Low)) occurs in each arbitrary position in the unit duration, the brightness of the light emitter can be changed continuously. 
     For example, the information communication method may include sequentially displaying a plurality of images by switching between the plurality of images, wherein in the determining, each time an image is displayed in the sequentially displaying, the pattern of the change in luminance for identification information corresponding to the displayed image is determined by modulating the identification information as the signal, and in the transmitting, each time the image is displayed in the sequentially displaying, the identification information corresponding to the displayed image is transmitted by the light emitter changing in luminance according to the pattern of the change in luminance determined for the identification information. 
     In this way, each time an image is displayed, the identification information corresponding to the displayed image is transmitted, for instance as illustrated in  FIG. 393 . Based on the displayed image, the user can easily select the identification information to be received by the receiver. 
     For example, in the transmitting, each time the image is displayed in the sequentially displaying, identification information corresponding to a previously displayed image may be further transmitted by the light emitter changing in luminance according to the pattern of the change in luminance determined for the identification information. 
     In this way, even in the case where, as a result of switching the displayed image, the receiver cannot receive the identification signal transmitted before the switching, the receiver can appropriately receive the identification information transmitted before the switching because the identification information corresponding to the previously displayed image is transmitted together with the identification information corresponding to the currently displayed image, for instance as illustrated in  FIG. 394 . 
     For example, in the determining, each time the image is displayed in the sequentially displaying, the pattern of the change in luminance for the identification information corresponding to the displayed image and a time at which the image is displayed may be determined by modulating the identification information and the time as the signal, and in the transmitting, each time the image is displayed in the sequentially displaying, the identification information and the time corresponding to the displayed image may be transmitted by the light emitter changing in luminance according to the pattern of the change in luminance determined for the identification information and the time, and the identification information and a time corresponding to the previously displayed image may be further transmitted by the light emitter changing in luminance according to the pattern of the change in luminance determined for the identification information and the time. 
     In this way, each time an image is displayed, a plurality of sets of ID time information (information made up of identification information and a time) are transmitted, for instance as illustrated in  FIG. 394 . The receiver can easily select, from the received plurality of sets of ID time information, a previously transmitted identification signal which the receiver cannot be received, based on the time included in each set of ID time information. 
     For example, the light emitter may have a plurality of areas each of which emits light, and in the transmitting, in the case where light from adjacent areas of the plurality of areas interferes with each other and only one of the plurality of areas changes in luminance according to the determined pattern of the change in luminance, only an area located at an edge from among the plurality of areas may change in luminance according to the determined pattern of the change in luminance. 
     In this way, only the area (light emitting unit) located at the edge changes in luminance, for instance as illustrated in (a) in  FIG. 387B . The influence of light from another area on the luminance change can therefore be suppressed as compared with the case where only an area not located at the edge changes in luminance. As a result, the receiver can capture the luminance change pattern appropriately. 
     For example, in the transmitting, in the case where only two of the plurality of areas change in luminance according to the determined pattern of the change in luminance, the area located at the edge and an area adjacent to the area located at the edge from among the plurality of areas may change in luminance according to the determined pattern of the change in luminance. 
     In this way, the area (light emitting unit) located at the edge and the area (light emitting unit) adjacent to the area located at the edge change in luminance, for instance as illustrated in (b) in  FIG. 387 . The spatially continuous luminance change range has a wide area, as compared with the case where areas apart from each other change in luminance. As a result, the receiver can capture the luminance change pattern appropriately. 
     An information communication method in this embodiment is an information communication method of obtaining information from a subject, the information communication method including: transmitting position information indicating a position of an image sensor used to capture the subject; receiving an ID list that is associated with the position indicated by the position information and includes a plurality of sets of identification information; setting an exposure time of the image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image including the bright line, by capturing the subject that changes in luminance by the image sensor with the set exposure time; obtaining the information by demodulating data specified by a pattern of the bright line included in the obtained bright line image; and searching the ID list for identification information that includes the obtained information. 
     In this way, since the ID list is received beforehand, even when the obtained information “bc” is only a part of identification information, the appropriate identification information “abcd” can be specified based on the ID list, for instance as illustrated in  FIG. 389 . 
     For example, in the case where the identification information that includes the obtained information is not uniquely specified in the searching, the obtaining of a bright line image and the obtaining of the information may be repeated to obtain new information, and the information communication method may further include searching the ID list for the identification information that includes the obtained information and the new information. 
     In this way, even in the case where the obtained information “b” is only a part of identification information and the identification information cannot be uniquely specified with this information alone, the new information “c” is obtained and so the appropriate identification information “abcd” can be specified based on the new information and the ID list, for instance as illustrated in  FIG. 389 . 
     An information communication method in this embodiment is an information communication method of obtaining information from a subject, the information communication method including: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image including the bright line, by capturing the subject that changes in luminance by the image sensor with the set exposure time; obtaining identification information by demodulating data specified by a pattern of the bright line included in the obtained bright line image; transmitting the obtained identification information and position information indicating a position of the image sensor; and receiving error notification information for notifying an error, in the case where the obtained identification information is not included in an ID list that is associated with the position indicated by the position information and includes a plurality of sets of identification information. 
     In this way, the error notification information is received in the case where the obtained identification information is not included in the ID list, for instance as illustrated in  FIG. 391 . Upon receiving the error notification information, the user of the receiver can easily recognize that information associated with the obtained identification information cannot be obtained. 
     Embodiment 16 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as a blink pattern of an LED, an organic EL device, or the like in Embodiments 1 to 15 described above, according to situation. 
     (Situation: In Front of Store) 
     An example of application in a situation where a user carrying a receiver is in front of a store bearing an advertisement sign which functions as a transmitter is described first, with reference to  FIGS. 409 to 413 . 
       FIG. 409  is a diagram illustrating an example of operation of a receiver in the in-front-of-store situation. 
     For example, when a user carrying a receiver  8300  (terminal device) such as a smartphone is walking, the user finds a sign  8301  of a store. The sign  8301  is a transmitter (subject) that transmits a signal using a change in luminance, like the transmitter in any of Embodiments 1 to 15 described above. The user is interested in the store and, upon determining that the sign  8301  is transmitting a signal by changing in luminance, operates the receiver  8300  to start visible light communication application software (hereafter referred to as “communication application”) of the receiver  8300 . 
       FIG. 410  is a diagram illustrating another example of operation of the receiver  8300  in the in-front-of-store situation. 
     The receiver  8300  may automatically start the communication application, without being operated by the user. For example, the receiver  8300  detects the current position of the receiver  8300  using a GPS, a 9-axis sensor, or the like, and determines whether or not the current position is in a predetermined specific area for the sign  8301 . The specific area is an area near the sign  8301 . In the case of determining that the current position of the receiver  8300  is in the specific area, the receiver  8300  starts the communication application. The receiver  8300  may also start the communication application upon detecting, through its 9-axis sensor or the like, the user sticking the receiver  8300  out or turning the receiver  8300 . This saves the user operation, and provides ease of use. 
       FIG. 411  is a diagram illustrating an example of next operation of the receiver  8300  in the in-front-of-store situation. 
     After starting the communication application as described above, the receiver  8300  captures (visible light imaging) the sign  8301  that functions as a transmitter for transmitting a signal using a change in luminance. That is, the receiver  8300  performs visible light communication with the sign  8301 . 
       FIG. 412  is a diagram illustrating an example of next operation of the receiver  8300  in the in-front-of-store situation. 
     The receiver  8300  obtains an image including a bright line, as a result of capturing the sign  8301 . The receiver  8300  obtains a device ID of the sign  8301 , by demodulating data specified by the pattern of the bright line. That is, the receiver  8300  obtains the device ID from the sign  8301 , by visible light imaging or visible light communication in Embodiments 1 to 15. The receiver  8300  transmits the device ID to a server, and obtains advertisement information (service information) associated with the device ID from the server. 
     The receiver  8300  may obtain the advertisement information associated with the device ID, from a plurality of sets of advertisement information held beforehand. In this case, when determining that the current position of the receiver  8300  is in the above-mentioned specific area, the receiver  8300  notifies the server of the specific area or the current position, and obtains all device IDs corresponding to the specific area and advertisement information associated with each of the device IDs from the server and holds (caches) them beforehand. By doing so, upon obtaining the device ID of the sign  8301  in the specific area, the receiver  8300  can promptly obtain the advertisement information associated with the device ID of the sign  8301  from the pre-stored advertisement information associated with each device ID, with no need to request the advertisement information associated with the device ID from the server. 
     Upon obtaining the advertisement information associated with the device ID of the sign  8301 , the receiver  8300  displays the advertisement information. For instance, the receiver  8300  displays a coupon and availability of the store shown by the sign  8301  and a barcode indicating the same contents. 
     The receiver  8300  may obtain not only the device ID but also privilege data from the sign  8301  by visible light communication. For example, the privilege data indicates a random ID (random number), the time at which or period during which the privilege data is transmitted, or the like. In the case of receiving the privilege data, the receiver  8300  transmits the privilege data to the server together with the device ID. The receiver  8300  then obtains advertisement information associated with the device ID and the privilege data. The receiver  8300  can thus receive different advertisement information according to the privilege data. As an example, if the sign  8301  is captured early in the morning, the receiver  8300  can obtain and display advertisement information indicating an early bird discount coupon. In other words, the advertisement by the same sign can be varied according to the privilege data (e.g. hours). As a result, the user can be provided with a service suitable for hours and the like. In this embodiment, the presentation (display) of information such as service information to the user is referred to as “service provision”. 
     The receiver  8300  may also obtain, by visible light communication, 3D information indicating the spatial placement of the sign  8301  with high accuracy (within a tolerance of 1 m), from the sign  8301  together with the device ID. Alternatively, the receiver  8300  may obtain the 3D information associated with the device ID from the server. The receiver  8300  may obtain size information indicating the size of the sign  8301 , Instead of or together with the 3D information. In the case of receiving the size information, the receiver  8300  can calculate the distance from the receiver  8300  to the sign  8301 , based on the difference between the size of the sign  8301  indicated by the size information and the size of the sign  8301  shown in the captured image. 
     Moreover, when transmitting the device ID obtained by visible light communication to the server, the receiver  8300  may transmit retention information (ancillary information) retained in the receiver  8300  to the server together with the device ID. For instance, the retention information is personal information (e.g. age, sex) or a user ID of the user of the receiver  8300 . Having received the retention information together with the device ID, the server transmits advertisement information associated with the retention information (the personal information or user ID) from among one or more sets of advertisement information associated with the device ID, to the receiver  8300 . The receiver  8300  can thus receive store advertisement information suitable for the personal information and the like, store advertisement information corresponding to the user ID, or the like. As a result, the user can be provided with a more valuable service. 
     As an alternative, the retention information indicates a reception condition set in the receiver  8300  beforehand. For example, in the case where the store is a restaurant, the reception condition is the number of customers. Having received such retention information together with the device ID, the server transmits advertisement information associated with the reception condition (the number of customers) from among one or more sets of advertisement information associated with the device ID, to the receiver  8300 . The receiver  8300  can thus receive store advertisement information suitable for the number of customers, such as availability information for the number of customers. The store can achieve customer attraction and profit optimization, by displaying advertisement information with a different discount rate according to the number of customers, the day of the week, or the time of day. 
     As another alternative, the retention information indicates the current position detected by the receiver  8300  beforehand. Having received such retention information together with the device ID, the server transmits not only advertisement information associated with the device ID but also one or more other device IDs corresponding to the current position (the current position and its surroundings) indicated by the retention information and advertisement information associated with each of the other device IDs, to the receiver  8300 . The receiver  8300  can cache the other device IDs and the advertisement information associated with each of the other device IDs. Accordingly, when the receiver  8300  performs visible light communication with another transmitter in the current position (the current position and its surroundings), the receiver  8300  can promptly obtain advertisement information associated with the device ID of this other transmitter, with no need to access the server. 
       FIG. 413  is a diagram illustrating an example of next operation of the receiver  8300  in the in-front-of-store situation. 
     Upon obtaining the advertisement information from the server as described above, the receiver  8300  displays, for example, the “Seats available” button as the availability indicated by the advertisement information. When the user performs an operation of touching the “Seats available” button with his or her finger, the receiver  8300  notifies the server of the operation. When notified of the operation, the server makes a provisional reservation at the store of the sign  8301 , and notifies the receiver  8300  of the completion of the provisional reservation. The receiver  8300  receives the notification from the server, and displays the character string “Provisional reservation” indicating the completion of the provisional reservation, instead of the “Seats available” button. The receiver  8300  stores an image including: the coupon of the store shown by the sign  8301 ; the character string “Provisional reservation” proving the provisional reservation at the store; and a barcode indicating the same contents, in a memory as a prior obtainment image. 
     Here, the server can log information relating to visible light communication performed between the sign  8301  and the receiver  8300 , by the operation described with reference to  FIGS. 412 and 413 . In detail, the server can log the device ID of the transmitter (sign) performing visible light communication, the location where visible light communication is performed (the current position of the receiver  8300 ), the privilege data indicating, for example, the time when visible light communication is performed, the personal information of the user of the receiver  8300  performing visible light communication, and so on. Through the use of at least one of these logged sets of information, the server can analyze the value of the sign  8301 , i.e. the contribution of the sign  8301  to the advertisement of the store, as advertising effectiveness. 
     (Situation: In Store) 
     An example of application in a situation where the user carrying the receiver  8300  enters the store corresponding to the displayed advertisement information (service information) is described next, with reference to  FIGS. 414 to 422 . 
       FIG. 414  is a diagram illustrating an example of operation of a display device in the in-store situation. 
     For example, the user of the receiver  8300  that has performed visible light communication with the above-mentioned sign  8301  enters the store corresponding to the displayed advertisement information. At this time, the receiver  8300  detects the user entering the store corresponding to the advertisement information displayed using visible light communication (i.e. detects the entrance). For instance, after performing visible light communication with the sign  8301 , the receiver  8300  obtains store information indicating the location of the store associated with the device ID of the sign  8301 , from the server. The receiver  8300  then determines whether or not the current position of the receiver  8300  obtained using the GPS, the 9-axis sensor, or the like enters the location of the store indicated by the store information. The receiver  8300  detects the above-mentioned entrance, by determining that the current position enters the location of the store. 
     Upon detecting the entrance, the receiver  8300  notifies a display device  8300   b  of the entrance, via the server or the like. Alternatively, the receiver  8300  notifies the display device  8300   b  of the entrance by visible light communication or wireless communication. When notified of the entrance, the display device  8300   b  obtains product service information indicating, for example, a menu of products or services provided in the store, and displays the menu indicated by the product service information. The display device  8300   b  may be a mobile terminal carried by the user of the receiver  8300  or the store staff, or a device installed in the store. 
       FIG. 415  is a diagram illustrating an example of next operation of the display device  8300   b  in the in-store situation. 
     The user selects a desired product from the menu displayed on the display device  8300   b . In detail, the user performs an operation of touching the part of the menu where the name of the desired product is displayed. The display device  8300   b  receives the product selection operation result. 
       FIG. 416  is a diagram illustrating an example of next operation of the display device  8300   b  in the in-store situation. 
     Upon receiving the product selection operation result, the display device  8300   b  displays an image representing the selected product and the price of the product. The display device  8300   b  thus prompts the user to confirm the selected product. The image representing the product, information indicating the price of the product, and the like are included, for example, in the above-mentioned product service information. 
       FIG. 417  is a diagram illustrating an example of next operation of the receiver  8300  in the in-store situation. 
     When prompted to confirm the selected product, the user performs an operation for ordering the product. After the operation is performed, the receiver  8300  notifies payment information necessary for electronic payment to a POS (Point of Sale) system of the store via the display device  8300   b  or the server. The receiver  8300  also determines whether or not there is the above-mentioned prior obtainment image which is obtained using visible light communication with the sign  8301  of the store and stored. In the case of determining that there is the prior obtainment image, the receiver  8300  displays the prior obtainment image. 
     Though the display device  8300   b  is used in this situation, the receiver  8300  may perform the processes by the display device  8300   b  instead, without using the display device  8300   b . In this case, upon detecting the entrance, the receiver  8300  obtains, from the server, the product service information indicating, for example, the menu of products or services provided in the store, and displays the menu indicated by the product service information. Moreover, upon receiving the operation for ordering the product, the receiver  8300  notifies the ordered product and the payment information necessary for electronic payment, to the POS system of the store via the server. 
       FIG. 418  is a diagram illustrating an example of next operation of the receiver  8300  in the in-store situation. 
     The store staff applies a barcode scanner  8302  of the POS system to the barcode in the prior obtainment image displayed on the receiver  8300 . The barcode scanner  8302  reads the barcode in the prior obtainment image. As a result, the POS system completes the electronic payment according to the coupon indicated by the barcode. The barcode scanner  8302  of the POS system then transmits, to the receiver  8300 , payment completion information indicating the completion of the electronic payment, by changing in luminance. Thus, the barcode scanner  8302  also has a function as a transmitter in visible light communication. The receiver  8300  receives the payment completion information by visible light communication, and displays the payment completion information. For example, the payment completion information indicates the message “Thank you for your purchase” and the amount paid. As a result of such electronic payment, the POS system, the server, and the receiver  8300  can determine that, in the store corresponding to the advertisement information (service information) displayed in front of the store, the user uses the service indicated by the advertisement information. 
     As described above, the product in the store is ordered through the operation of the receiver  8300 , the POS system, and the like as illustrated in  FIGS. 414 to 418 . Accordingly, the user who has entered the store can order the product from the menu of the store automatically displayed on the display device  8300   b  or the receiver  8300 . In other words, there is no need for the store staff to show the menu to the user and directly receive the order for the product from the user. This significantly reduces the burden on the store staff. Though the barcode scanner  8302  reads the barcode in the above example, the barcode scanner  8302  may not be used. For instance, the receiver  8300  may transmit the information indicated by the barcode, to the POS system via the server. The receiver  8300  may then obtain the payment completion information from the POS system via the server. This further reduces the store staff&#39;s workload, and allows the user to order the product without the store staff. Alternatively, the display device  8300   b  and the receiver  8300  may transfer the order and charging data with each other by visible light communication, or transfer the data by wireless communication using a key exchanged by visible light communication. 
     There is the case where the sign  8301  is displayed by one of a plurality of stores belonging to a chain. In such a case, the advertisement information obtained from the sign  8301  using visible light communication can be used in all stores of the chain. Here, the service provided to the user may be different between a store (advertisement store) displaying the sign  8301  and a store (non-advertisement store) not displaying the sign  8301 , even though they belong to the same chain. For example, in the case where the user enters the non-advertisement store, the user receives the service of the discount rate (e.g. 20%) according to the coupon indicated by the prior obtainment image. In the case where the user enters the advertisement store, the user receives the service of a higher discount rate (e.g. 30%) than the discount rate of the coupon. In detail, in the case of detecting the entrance into the advertisement store, the receiver  8300  obtains additional service information indicating an additional discount of 10% from the server, and displays an image indicating a discount rate of 30% (20%+10%) instead of the prior obtainment image illustrated in  FIG. 417 . Here, the receiver  8300  detects whether the user enters the advertisement store or the non-advertisement store, based on the above-mentioned store information obtained from the server. The store information indicates the location of each of the plurality of stores belonging to the chain, and whether the store is the advertisement store or the non-advertisement store. 
     In the case where a plurality of non-advertisement stores are included in the chain, the service provided to the user may be different in each of the non-advertisement stores. For instance, the service according to the distance from the position of the sign  8301  or the current position of the receiver  8300  when performing visible light communication with the sign  8301  to the non-advertisement store is provided to the user entering the non-advertisement store. Alternatively, the service according to the difference (time difference) between the time at which the receiver  8300  and the sign  8301  perform visible light communication and the time at which the user enters the non-advertisement store is provided to the user entering the non-advertisement store. That is, the receiver  8300  obtains, from the server, additional service information indicating an additional discount that differs depending on the above-mentioned distance (the position of the sign  8301 ) and time difference, and displays an image indicating a discount rate (e.g. 30%) on which the additional discount has been reflected, instead of the prior obtainment image illustrated in  FIG. 417 . Note that such a service is determined by the server or the POS system, or by cooperation between the server and the POS system. The service may be applied to every store belonging to the chain, regardless of whether the store is the advertisement store or the non-advertisement store. 
     In the case where the user enters the non-advertisement store and makes the order using the advertisement information, the POS system of the non-advertisement store may pass part of the amount earned as a result of the order, to the POS system of the advertisement store. 
     Each time the advertisement information is displayed, the server may determine whether or not the advertisement information is used. By collecting the determination results, the server can easily analyze the advertising effectiveness of the sign  8301 . Moreover, by collecting at least one of: the position of the sign  8301 ; the time at which the advertisement information is displayed; the position of the store in which the advertisement information is used; the time at which the advertisement information is used; and the time at which the user enters the store, the server can improve the accuracy of analyzing the advertising effectiveness of the sign  8301 , and find the position of the sign  8301  highest in advertising effectiveness. 
     The receiver  8300  may also obtain, from the server, additional service information indicating an additional discount corresponding to the number of times the advertisement information is used to order the product (the number of uses), and display an image indicating a discount rate (e.g. 30%) on which the additional discount corresponding to the number of uses has been reflected, instead of the prior obtainment image illustrated in  FIG. 417 . For example, the server may provide such a service that sets a higher discount rate when the number of uses is larger, in cooperation with the POS system. 
     In the case where the receiver  8300  receives advertisement information associated with each of the device IDs of all signs  8301  displayed by the store (i.e. in the case where the obtainment of all advertisement information is completed), the server may provide a good-value service to the user entering the store of the sign  8301 . Examples of the good-value service include a service of a very high discount rate and a service of offering a product other than the ordered product free of charge. When the receiver  8300  detects the entrance of the user into the store, the server determines whether or not the receiver  8300  has performed the process including visible light communication and the like on each of all signs associated with the store. In the case where the server determines that the receiver  8300  has performed the process, the receiver  8300  obtains additional service information indicating an additional discount from the server as the above-mentioned good-value service, and displays an image indicating a discount rate (e.g. 50%) on which the additional discount has been reflected, instead of the prior obtainment image illustrated in  FIG. 417 . 
     The receiver  8300  may also obtain, from the server, additional service information indicating an additional discount that differs depending on the difference between the time at which the receiver  8300  performs visible light communication with the sign  8301  and displays the advertisement information and the time at which the user enters the store, and display an image indicating a discount rate (e.g. 30%) on which the additional discount has been reflected, Instead of the prior obtainment image illustrated in  FIG. 417 . For instance, the receiver  8300  obtains additional service information indicating a higher discount rate when the difference is smaller, from the server. 
       FIG. 419  is a diagram illustrating an example of next operation of the receiver  8300  in the in-store situation. 
     Having completed the order and the electronic payment, the receiver  8300  receives a signal transmitted from a transmitter such as a lighting device in the store by changing in luminance, and transmits the signal to the server, thus obtaining an in-store guide map indicating the seat position (e.g. black circle) of the user. The receiver  8300  also specifies the position of the receiver  8300  using the received signal, as in any of Embodiments 1 to 15 described above. The receiver  8300  displays the specified position (e.g. star) of the receiver  8300  in the guide map. This enables the user to easily find the way to his or her seat. 
     While the user is moving, too, the receiver  8300  frequently specifies the position of the receiver  8300  by performing visible light communication with a nearby transmitter such as a lighting device in the store. Hence, the receiver  8300  sequentially updates the displayed position (e.g. start) of the receiver  8300 . The user can be appropriately guided to the seat in this manner. 
       FIG. 420  is a diagram illustrating an example of next operation of the receiver  8300  in the in-store situation. 
     When the user is seated, the receiver  8300  specifies the position of the receiver  8300  by performing visible light communication with a transmitter  8303  such as a lighting device, and determines that the position is the seat position of the user. The receiver  8300  notifies, together with the user name or nickname, that the user is seated, to a terminal in the store via the server. This enables the store staff to recognize which seat the user is in. 
       FIG. 421  is a diagram illustrating an example of next operation of the receiver  8300  in the in-store situation. 
     The transmitter  8303  transmits a signal including a customer ID and a message informing that the ordered product is ready, by changing in luminance. Note that, for example when obtaining the product service information indicating the product menu and the like from the server, the receiver  8300  also obtains the customer ID from the server and holds it. The receiver  8300  receives the signal, by performing visible light imaging on the transmitter  8303 . The receiver  8300  determines whether or not the customer ID included in the signal matches the customer ID held beforehand. In the case of determining that they match, the receiver  8300  displays the message (e.g. “Your order is ready”) included in the signal. 
       FIG. 422  is a diagram illustrating an example of next operation of the receiver  8300  in the in-store situation. 
     The store staff, having delivered the ordered product to the user&#39;s seat, directs a handheld terminal  8302   a  to the receiver  8300  in order to prove that the ordered product has been delivered. The handheld terminal  8302   a  functions as a transmitter. The handheld terminal  8302   a  transmits, to the receiver  8300 , a signal indicating the delivery of the ordered product by changing in luminance. The receiver  8300  captures the handheld terminal  8302   a  to receive the signal, and displays a message (e.g. “Please enjoy your meal”) indicated by the signal. 
     (Situation: Store Search) 
     An example of application in a situation where the user carrying the receiver  8300  is searching for a store of interest is described below, with reference to  FIGS. 423 to 425 . 
       FIG. 423  is a diagram illustrating an example of operation of the receiver  8300  in the store search situation. 
     The user finds a signage  8304  showing restaurants of interest. Upon determining that the signage  8304  is transmitting a signal by changing in luminance, the user operates the receiver  8300  to start the communication application of the receiver  8300 , as in the example illustrated in  FIG. 409 . Alternatively, the receiver  8300  may automatically start the communication application as in the example illustrated in  FIG. 410 . 
       FIG. 424  is a diagram illustrating an example of next operation of the receiver  8300  in the store search situation. 
     The receiver  8300  captures the entire signage  8304  or a part of the signage  8304  showing a restaurant of the user&#39;s interest, to receive an ID for identifying the signage  8304  or the restaurant. 
       FIG. 425  is a diagram illustrating an example of next operation of the receiver  8300  in the store search situation. 
     Upon receiving the ID mentioned above, the receiver  8300  transmits the ID to the server, and obtains advertisement information (service information) associated with the ID from the server and displays it. Here, the receiver  8300  may notify the number of people (ancillary information) who are about to enter the restaurant, to the server together with the ID. As a result, the receiver  8300  can obtain advertisement information corresponding to the number of people. For example, the receiver  8300  can obtain advertisement information indicating that seats are available in the restaurant for the notified number of people. 
     (Situation: Movie Advertisement) 
     An example of application in a situation where the user carrying the receiver  8300  is in front of a signage including a movie advertisement of interest is described below, with reference to  FIGS. 426 to 429 . 
       FIG. 426  is a diagram illustrating an example of operation of the receiver  8300  in the movie advertisement situation. 
     The user finds a signage  8305  including a movie advertisement of interest, and a signage  8306  such as a liquid crystal display for displaying movie advertisement video. The signage  8305  includes, for example, a transparent film on which an image representing the movie advertisement is drawn, and a plurality of LEDs arranged on the back side of the film and lights the film. That is, the signage  8305  brightly displays the image drawn on the film by the light emission from the plurality of LEDs, as a still image. The signage  8305  is a transmitter for transmitting a signal by changing in luminance. 
     Upon determining that the signage  8305  is transmitting a signal by changing in luminance, the user operates the receiver  8300  to start the communication application of the receiver  8300 , as in the example illustrated in  FIG. 409 . Alternatively, the receiver  8300  may automatically start the communication application as in the example illustrated in  FIG. 410 . 
       FIG. 427  is a diagram illustrating an example of next operation of the receiver  8300  in the movie advertisement situation. 
     The receiver  8300  captures the signage  8305 , to obtain the ID of the signage  8305 . The receiver  8300  transmits the ID to the server, downloads movie advertisement video data associated with the ID from the server as service information, and reproduces the video. 
       FIG. 428  is a diagram illustrating an example of next operation of the receiver  8300  in the movie advertisement situation. 
     Video displayed by reproducing the downloaded video data as mentioned above is the same as the video displayed by the signage  8306  as an example. Accordingly, in the case where the user wants to watch the movie advertisement video, the user can watch the video in any location without stopping in front of the signage  8306 . 
       FIG. 429  is a diagram illustrating an example of next operation of the receiver  8300  in the movie advertisement situation. 
     The receiver  8300  may download not only the video data but also showing information indicating the showtimes of the movie and the like together with the video data, as service information. The receiver  8300  can then display the showing information to inform the user, and also share the showing information with other terminals (e.g. other smartphones). 
     (Situation: Museum) 
     An example of application in a situation where the user carrying the receiver  8300  enters a museum to appreciate each exhibit in the museum is described below, with reference to  FIGS. 430 to 435 . 
       FIG. 430  is a diagram illustrating an example of operation of the receiver  8300  in the museum situation. 
     For example, when entering the museum, the user finds a signboard  8307  on the entrance of the museum. Upon determining that the signboard  8307  is transmitting a signal by changing in luminance, the user operates the receiver  8300  to start the communication application of the receiver  8300 , as in the example illustrated in  FIG. 409 . Alternatively, the receiver  8300  may automatically start the communication application as in the example illustrated in  FIG. 410 . 
       FIG. 431  is a diagram illustrating an example of next operation of the receiver  8300  in the museum situation. 
     The receiver  8300  captures the signboard  8307 , to obtain the ID of the signboard  8307 . The receiver  8300  transmits the ID to the server, downloads a guide application program of the museum (hereafter referred to as “museum application”) from the server as service information associated with the ID, and starts the museum application. 
       FIG. 432  is a diagram illustrating an example of next operation of the receiver  8300  in the museum situation. 
     After the museum application starts, the receiver  8300  displays a museum guide map according to the museum application. The receiver  8300  also specifies the position of the receiver  8300  in the museum, as in any of Embodiments 1 to 15 described above. The receiver  8300  displays the specified position (e.g. star) of the receiver  8300  in the guide map. 
     To specify the position as mentioned above, the receiver  8300  obtains form information indicating the size, shape, and the like of the signboard  8307  from the server, for example when downloading the museum application. The receiver  8300  specifies the relative position of the receiver  8300  to the signboard  8307  by triangulation or the like, based on the size and shape of the signboard  8307  indicated by the form information and the size and shape of the signboard  8307  shown in the captured image. 
       FIG. 433  is a diagram illustrating an example of next operation of the receiver  8300  in the museum situation. 
     When the user enters the museum, the receiver  8300  which has started the museum application as mentioned above frequently specifies the position of the receiver  8300  by performing visible light communication with a nearby transmitter such as a lighting device in the museum. For example, the receiver  8300  captures a transmitter  8308  such as a lighting device, to obtain the ID of the transmitter  8308  from the transmitter  8308 . The receiver  8300  then obtains position information indicating the position of the transmitter  8308  and form information indicating the size, shape, and the like of the transmitter  8308  which are associated with the ID, from the server. The receiver  8300  estimates the relative position of the receiver  8300  to the transmitter  8308  by triangulation or the like, based on the size and shape of the transmitter  8308  indicated by the form information and the size and shape of the transmitter  8308  shown in the captured image. The receiver  8300  also specifies the position of the receiver  8300  in the museum, based on the position of the transmitter  8308  indicated by the position information obtained from the server and the estimated relative position of the receiver  8300 . 
     Each time the position of the receiver  8300  is specified, the receiver  8300  moves the displayed star to the specified new position. The user who has entered the museum can easily know his or her position in the museum, from the guide map and the star displayed on the receiver  8300 . 
       FIG. 434  is a diagram illustrating an example of next operation of the receiver  8300  in the museum situation. 
     The user who has entered the museum, upon finding an exhibit  8309  of interest, performs an operation of pointing the receiver  8300  at the exhibit  8309  so that the receiver  8300  can capture the exhibit  8309 . Here, the exhibit  8309  is lit by light from a lighting device  8310 . The lighting device  8310  is used exclusively for the exhibit  8309 , and is a transmitter for transmitting a signal by changing in luminance. Accordingly, the exhibit  8309  which is lit by the light changing in luminance is indirectly transmitting the signal from the lighting device  8310 . 
     Upon detecting the operation of pointing the receiver  8300  at the exhibit  8309  based on the output from the internal 9-axis sensor or the like, the receiver  8300  captures the exhibit  8309  to receive the signal from the lighting device  8310 . The signal indicates the ID of the exhibit  8309 , as an example. The receiver  8300  then obtains introduction information (service information) of the exhibit  8309  associated with the ID, from the server. The introduction information indicates a figure for introducing the exhibit  8309 , and text for introduction in the language of each country such as Japanese, English, and French. 
     Having obtained the introduction information from the server, the receiver  8300  displays the figure and the text indicated by the introduction information. When displaying the text, the receiver  8300  extracts text of a language set by the user beforehand from among text of each language, and displays only the text of the language. The receiver  8300  may change the language according to a selection operation by the user. 
       FIG. 435  is a diagram illustrating an example of next operation of the receiver  8300  in the museum situation. 
     After the display of the figure and the text in the introduction information ends according to a user operation, the receiver  8300  again specifies the position of the receiver  8300  by performing visible light communication with a nearby transmitter such as a lighting device (e.g. a lighting device  8311 ). Upon specifying the new position of the receiver  8300 , the receiver  8300  moves the displayed star to the specified new position. Hence, the user who has appreciated the exhibit  8309  can easily move to the next exhibit of interest, by referring to the guide map and the star displayed on the receiver  8300 . 
     (Situation: Bus Stop) 
     An example of application in a situation where the user carrying the receiver  8300  is at a bus stop is described below, with reference to  FIGS. 436 to 437 . 
       FIG. 436  is a diagram illustrating an example of operation of the receiver  8300  in the bus stop situation. 
     For example, the user goes to the bus stop to ride a bus. Upon determining that a sign  8312  at the bus stop is transmitting a signal by changing in luminance, the user operates the receiver  8300  to start the communication application of the receiver  8300 , as in the example illustrated in  FIG. 409 . Alternatively, the receiver  8300  may automatically start the communication application as in the example illustrated in  FIG. 410 . 
       FIG. 437  is a diagram illustrating an example of next operation of the receiver  8300  in the bus stop situation. 
     The receiver  8300  captures the sign  8312 , to obtain the ID of the bus stop where the sign  8312  is placed. The receiver  8300  transmits the ID to the server, and obtains operation state information associated with the ID from the server. The operation state information indicates the traffic state, and is service information indicating a service provided to the user. 
     Here, the server collects information from each bus operating in an area including the bus stop, to manage the operation state of each bus. Hence, upon obtaining the ID of the bus stop from the receiver  8300 , the server estimates the time at which a bus arrives at the bus stop of the ID based on the managed operation state, and transmits the operation state information indicating the estimated time to the receiver  8300 . 
     Having obtained the operation state information, the receiver  8300  displays the time indicated by the operation state information in a form such as “Arriving in 10 minutes”. This enables the user to easily recognize the operation state of the bus. 
     (Supplementary Note) 
     In the case where the scan direction on the imaging side is the vertical direction (up-down direction) of a mobile terminal, when an LED lighting device is captured with a shorter exposure time, bright lines of a black and white pattern can be captured in the same direction as the scan direction for ON/OFF of the entire LED lighting device, as illustrated in (a) in  FIG. 438 . In (a) in  FIG. 438 , a vertically long LED lighting device is captured so that its longitudinal direction is perpendicular to the scan direction on the imaging side (the left-right direction of the mobile terminal), and therefore many bright lines of the black and white pattern can be captured in the same direction as the scan direction. In other words, a larger amount of information can be transmitted and received. On the other hand, in the case where the vertically long LED lighting device is captured so as to be parallel to the scan direction on the imaging side (the up-down direction of the mobile terminal) as illustrated in (b) in  FIG. 438 , the number of bright lines of the black and white pattern that can be captured decreases. In other words, the amount of information that can be transmitted decreases. 
     Thus, depending on the direction of the LED lighting device with respect to the scan direction on the imaging side, many bright lines of the black and white pattern can be captured (in the case where the vertically long LED lighting device is captured so that its longitudinal direction is perpendicular to the scan direction on the imaging side) or only a few bright lines of the black and white pattern can be captured (in the case where the vertically long LED lighting device is captured so that its longitudinal direction is parallel to the scan direction on the imaging side). 
     This embodiment describes a lighting device control method capable of capturing many bright lines even in the case where only a few bright lines of the black and white pattern can be captured. 
       FIG. 439  illustrates an example of a lighting device having a plurality of LEDs in the vertical direction, and a drive signal for the lighting device. (a) in  FIG. 439  illustrates the lighting device having the plurality of LEDs in the vertical direction. Suppose each LED element corresponds to a smallest unit of horizontal stripes obtained by coding a visible light communication signal, and corresponds to a coded ON/OFF signal. By generating the black and white pattern and turning each LED element ON or OFF for lighting in this way, the black and white pattern on an LED element basis can be captured even when the scan direction on the imaging side and the longitudinal direction of the vertically long LED lighting device are parallel to each other. 
     (c) and (d) in  FIG. 439  illustrate an example of generating the black and white pattern and turning each LED element ON or OFF for lighting. When the lighting device lights as the black and white pattern, the light may become not uniform even in a short time. In view of this, an example of generating a reverse phase pattern and performing lighting alternately between the two patterns is illustrated in (c) and (d) in  FIG. 439 . Each element that is ON in (c) in  FIG. 439  is OFF in (d) in  FIG. 439 , whereas each element that is OFF in (c) in  FIG. 439  is ON in (d) in  FIG. 439 . By lighting in the black and white pattern alternately between the normal phase pattern and the reverse phase pattern in this way, a lot of information can be transmitted and received in visible light communication, without causing the light to become not uniform and without being affected by the relation between the scan direction on the imaging side and the direction of the lighting device. The present disclosure is not limited to the case of alternately generating two types of patterns, i.e. the normal phase pattern and the reverse phase pattern, for lighting, as three or more types of patterns may be generated for lighting.  FIG. 440  illustrates an example of lighting in four types of patterns in sequence. 
     A structure in which usually the entire LED lighting blinks ((b) in  FIG. 439 ) and, only for a predetermined time, the black and white pattern is generated to perform lighting on an LED element basis is also available. As an example, the entire LED lighting blinks for a transmission and reception time of a predetermined data unit, and subsequently lighting is performed in the black and white pattern on an LED element basis for a short time. The predetermined data unit is, for instance, a data unit from the first header to the next header. In this case, when the LED lighting is captured in the direction in (a) in  FIG. 438 , a signal is received from bright lines obtained by capturing the blink of the entire LED lighting. When the LED lighting is captured in the direction in (b) in  FIG. 438 , a signal is received from a light emission pattern on an LED element basis. 
     This embodiment is not limited to an LED lighting device, and is applicable to any device whose ON/OFF can be controlled in units of small elements like LED elements. Moreover, this embodiment is not limited to a lighting device, and is applicable to other devices such as a television, a projector, and a signage. 
     Though an example of lighting in the black and white pattern is described in this embodiment, colors may be used instead of the black and white pattern. As an example, in RGB, blink may be performed using only B, while R and G are constantly ON. The use of only B rather than R or G prevents recognition by humans, and therefore suppresses flicker. As another example, additive complementary colors (e.g. a red and cyan pattern, a green and magenta pattern, a yellow and blue pattern) may be used to display ON/OFF, instead of the black and white pattern. The use of additive complementary colors suppresses flicker. 
     Though an example of one-dimensionally arranging LED elements is described in this embodiment, LED elements may be arranged not one-dimensionally but two-dimensionally so as to be displayed like a 2D barcode. 
     Conclusion of this Embodiment 
     A service provision method in this embodiment is a service provision method of providing, using a terminal device that includes an image sensor having a plurality of exposure lines, a service to a user of the terminal device, the service provision method including: obtaining image data, by starting exposure sequentially for the plurality of exposure lines in the image sensor each at a different time and capturing a subject with an exposure time less than or equal to 1/480 second so that an exposure time of each of the plurality of exposure lines partially overlaps an exposure time of an adjacent one of the plurality of exposure lines; obtaining identification information of the subject, by demodulating a bright line pattern that appears in the image data, the bright line pattern corresponding to the plurality of exposure lines; and presenting service information associated with the identification information of the subject, to the user. 
     In this way, through the use of communication between the subject and the terminal device respectively as a transmitter and a receiver, the service information relating to the subject can be presented to the user of the terminal device. The user can thus be provided with information variable to the user in various forms, as a service. For example, in the presenting, at least one of: information indicating an advertisement, availability, or reservation status of a store relating to the subject; information indicating a discount rate of a product or a service; movie advertisement video; information indicating a showtime of a movie; information for guiding in a building; information for introducing an exhibit; and information indicating a traffic state may be presented as the service information. 
     For example, the service provision method may further include: transmitting, by the terminal device, the identification information of the subject to a server; and obtaining, by the terminal device, the service information associated with the identification information of the subject from the server, wherein in the presenting, the terminal device presents the obtained service information to the user. 
     In this way, the service information can be managed in the server in association with the identification information of the subject, which contributes to ease of maintenance such as service information update. 
     For example, in the transmitting, ancillary information may be transmitted to the server together with the identification information of the subject, and in the obtaining of the service information, the service information associated with the identification information of the subject and the ancillary information may be obtained. 
     In this way, a more suitable service for the user can be provided according to the ancillary information. For example, in the transmitting, personal information of the user, identification information of the user, number information indicating the number of people of a group including the user, or position information indicating a position of the terminal device may be transmitted as the ancillary information, as in the operation described with reference to  FIGS. 412 and 425 . 
     For example, the service provision method may further include: transmitting, by the terminal device, position information indicating a position of the terminal device to the server; and obtaining, by the terminal device, one or more sets of identification information of respective one or more devices located in a predetermined range including the position indicated by the position information and one or more sets of service information respectively associated with the one or more sets of identification information, from the server and holding the one or more sets of identification information and the one or more sets of service information, wherein in the presenting, the terminal device selects service information associated with the identification information of the subject from the one or more sets of service information held in the obtaining of the identification information, and presents the service information to the user. 
     In this way, when the terminal device obtains the identification information of the subject, the terminal device can obtain the service information associated with the identification information of the subject from the one or more sets of service information held beforehand and present the service information without communicating with the server or the like, as in the operation described with reference to  FIG. 410  as an example. Faster service provision can therefore be achieved. 
     For example, the service provision method may further include: determining whether or not the user enters a store corresponding to the service information presented in the presenting, by specifying a position of the user; and in the case of determining that the user enters the store, obtaining, by the terminal device, product service information relating to a product or a service of the store from the server, and presenting the product service information to the user. 
     In this way, when the user enters the store, the menu of the store or the like can be automatically presented to the user as the product service information, as in the operation described with reference to  FIGS. 414 to 418  as an example. This saves the need for the store staff to present the menu or the like to the user, and enables the user to make an order to the store in a simple manner. 
     For example, the service provision method may further include: determining whether or not the user enters a store corresponding to the service information presented in the presenting, by specifying a position of the user; and in the case of determining that the user enters the store, presenting, by the terminal device, additional service information of the store to the user, the additional service information being different depending on at least one of the position of the subject and a time at which the service information is presented. 
     In this way, when the subject is closer to the store which the user enters or when the time at which the user enters the store and the time at which the service information is presented (or the time at which the subject is captured) are closer to each other, service information more valuable to the user can be presented to the user as the additional service information, as in the process described with reference to  FIGS. 414 to 418  as an example. Suppose each of a plurality of stores belonging to a chain is a store corresponding to the presented service information, and a sign which is the subject is displayed by one (advertisement store) of the plurality of stores. In such a case, the advertisement store is usually closest to the subject (sign) from among the plurality of stores belonging to the chain. Accordingly, when the subject is closer to the store which the user enters or when the time at which the user enters the store and the time at which the service information is presented are closer to each other, there is a high possibility that the store which the user enters is the advertisement store. In the case where there is a high possibility that the user enters the advertisement store, service information more valuable to the user can be presented to the user as the additional service information. 
     For example, the service provision method may further include: determining whether or not the user enters a store corresponding to the service information presented in the presenting, by specifying a position of the user; and in the case of determining that the user enters the store, presenting, by the terminal device, additional service information of the store to the user, the additional service information being different depending on the number of times the user uses a service indicated by the service information in the store. 
     In this way, when the number of times the service is used is larger, service information more valuable to the user can be presented to the user as the additional service information, as in the operation described with reference to  FIGS. 414 to 418  as an example. For instance, when the number of uses of service information indicating 20% product price discount exceeds a threshold, additional service information indicating additional 10% discount can be presented to the user. 
     For example, the service provision method may further include: determining whether or not the user enters a store corresponding to the service information presented in the presenting, by specifying a position of the user; in the case of determining that the user enters the store, determining whether or not a process including the obtaining of image data, the obtaining of identification information, and the presenting is also performed for all subjects associated with the store other than the subject; and presenting, by the terminal device, additional service information of the store to the user in the case of determining that the process is performed. 
     In this way, for instance in the case where the store displays several subjects as signs and the obtaining of image data, the obtaining of identification information, and the presenting have been performed for all of these signs, service information most valuable to the user can be presented to the user as the additional service information, as in the operation described with reference to  FIGS. 414 to 418  as an example. 
     For example, the service provision method may further include: determining whether or not the user enters a store corresponding to the service information presented in the presenting, by specifying a position of the user; and in the case of determining that the user enters the store, presenting, by the terminal device, additional service information of the store to the user, the additional service information being different depending on a difference between a time at which the service information is presented and a time at which the user enters the store. 
     In this way, when the difference between the time at which the service information is presented (or the time at which the subject is captured) and the time at which the user enters the store is smaller, service information more valuable to the user can be presented to the user as the additional service information, as in the operation described with reference to  FIGS. 414 to 418  as an example. That is, the time from when the service information is presented to the user as a result of capturing the subject to when the user enters the store is shorter, the user is additionally provided with a more valuable service. 
     For example, the service provision method may further include: determining whether or not the user uses a service indicated by the service information in a store corresponding to the service information presented in the presenting; and accumulating, each time the service information is presented, a determination result in the determining, and analyzing an advertising effect of the subject based on an accumulation result. 
     In this way, in the case where the service information indicates a service such as 20% product price discount or the like, it is determined whether or not the service is used by electronic payment or the like, as in the operation described with reference to  FIGS. 414 to 418  as an example. Thus, each time the service is provided to the user upon capturing the subject, whether or not the service is used is determined. As a result, the advertising effect of the subject is analyzed as high in the case where, for example, it is frequently determined that the service is used. Hence, the advertising effect of the subject can be appropriately analyzed based on the use result. 
     For example, in the analyzing, at least one of a position of the subject, a time at which the service information is presented, a position of the store, and a time at which the user enters the store may be accumulated together with the determination result in the determining, to analyze the advertising effect of the subject based on an accumulation result. 
     In this way, the advertising effect of the subject can be analyzed in more detail. For instance, in the case where the position of the subject is changed, it is possible to compare the advertising effect between the original position and the changed position, as a result of which the subject can be displayed at a position with higher advertising effectiveness. 
     For example, the service provision method may further include: determining whether or not the user uses a service indicated by the service information in a store corresponding to the service information presented in the presenting; in the case of determining that the user uses the service, determining whether or not a used store which is the store where the service is used is a specific store associated with the subject; and in the case of determining that the used store is not the specific store, returning at least a part of an amount paid for using the service in the store, to the specific store using electronic commerce. 
     In this way, even in the case where the service is not used in the specific store (e.g. the advertisement store displaying the sign which is the subject), the specific store can earn a profit for the cost of installing the sign which is the subject, as in the operation described with reference to  FIGS. 414 to 418  as an example. 
     For example, in the presenting, the terminal device may present the service information for introducing the subject to the user in the case where the subject lit by light changing in luminance is captured in the obtaining of the image data, and the terminal device may present the service information for guiding in a building in which the subject is placed in the case where a lighting device changing in luminance is captured as the subject in the obtaining of the image data. 
     In this way, a guide service in a building such as a museum and an introduction service for an exhibit which is the subject can be appropriately provided to the user, as in the operation described with reference to  FIGS. 433 and 434  as an example. 
     An information communication method in this embodiment is an information communication method of obtaining information from a subject having a plurality of light emitting elements, the information communication method including: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a bright line corresponding to an exposure line included in the image sensor appears according to a change in luminance of the subject; obtaining a bright line image by capturing, by the image sensor with the set exposure time, the subject in which the plurality of light emitting elements all change in luminance in the same manner according to a pattern of the change in luminance for representing first information, the bright line image being an image including the bright line; obtaining the first information by demodulating data specified by a pattern of the bright line included in the obtained bright line image; and obtaining second information, by capturing the subject in which each of the plurality of light emitting elements emits light with one of two different luminance values and demodulating data specified by a light and dark sequence of luminance along a direction parallel to the exposure line, the light and dark sequence being shown in an image obtained by capturing the subject. 
     Alternatively, an information communication method in this embodiment is an information communication method of transmitting a signal using a change in luminance, the information communication method including: determining a pattern of the change in luminance, by modulating a first signal to be transmitted; transmitting the first signal, by all of a plurality of light emitting elements in a light emitter changing in luminance in the same manner according to the determined pattern of the change in luminance; and transmitting a second signal to be transmitted, by each of the plurality of light emitting elements emitting light with one of two different luminance values so that a light and dark sequence of luminance appears in a space where the light emitter is placed. 
     In this way, even when a lighting device which is the subject or the light emitter has a long and thin shape including a plurality of LEDs arranged in a line, the receiver can appropriately obtain the information or signal from the lighting device regardless of the imaging direction, as in the operation described with reference to  FIGS. 438 to 440  as an example. In detail, in the case where the exposure line (the operation direction on the imaging side) of the image sensor included in the receiver is not parallel to the arrangement direction of the plurality of LEDs, the receiver can appropriately obtain the information or signal from the luminance change of the entire lighting device. Even in the case where the exposure line is parallel to the arrangement direction, the receiver can appropriately obtain the information or signal from the light and dark sequence of luminance along the direction parallel to the exposure line. In other words, the dependence of information reception on the imaging direction can be reduced. 
     Embodiment 17 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as a blink pattern of an LED, an organic EL device, or the like in Embodiments 1 to 16 described above. 
       FIG. 441  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     Transmitters  8321 ,  8322 , and  8323  each have the same function as the transmitter in any of Embodiments 1 to 16 described above, and is a lighting device that transmits a signal by changing in luminance (visible light communication). The transmitters  8321  to  8323  each transmit a signal by changing in luminance at a different frequency. For example, the transmitter  8321  transmits the ID “1000” of the transmitter  8321 , by changing in luminance at frequency a (e.g. 9200 Hz). The transmitter  8322  transmits the ID “2000” of the transmitter  8322 , by changing in luminance at frequency b (e.g. 9600 Hz). The transmitter  8323  transmits the ID “3000” of the transmitter  8322 , by changing in luminance at frequency c (e.g. 10000 Hz). 
     A receiver captures (visible light imaging) the transmitters  8321  to  8323  so that the transmitters  8321  to  8323  are all included in the angle of view, in the same way as in Embodiments 1 to 16. A bright line pattern corresponding to each transmitter appears in an image obtained as a result of image capture. It is possible to specify, from the bright line pattern, the luminance change frequency of the transmitter corresponding to the bright line pattern. 
     Suppose the frequencies of the transmitters  8321  to  8323  are the same. In such a case, the same frequency is specified from the bright line pattern corresponding to each transmitter. In the case where these bright line patterns are adjacent to each other, it is difficult to distinguish between the bright line patterns because the frequency specified from each of the bright line patterns is the same. 
     In view of this, the transmitters  8321  to  8323  each change in luminance at a different frequency, as mentioned above. As a result, the receiver can easily distinguish between the bright line patterns and, by demodulating data specified by each bright line pattern, appropriately obtain the ID of each of the transmitters  8321  to  8323 . Thus, the receiver can appropriately distinguish between the signals from the transmitters  8321  to  8323 . 
     The frequency of each of the transmitters  8321  to  8323  may be set by a remote control, and may be set randomly. Each of the transmitters  8321  to  8323  may communicate with its adjacent transmitter, and automatically set the frequency of the transmitter so as to be different from the frequency of the adjacent transmitter. 
       FIG. 442  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     In the above example, each transmitter changes in luminance at a different frequency. In the case where there are at least five transmitters, however, each transmitter need not change in luminance at a different frequency. In detail, each of the at least five transmitters may change in luminance at any one of four types of frequencies. 
     For example as shown in  FIG. 442 , even in a situation where the bright line patterns (rectangles in  FIG. 442 ) respectively corresponding to the at least five transmitters are adjacent, the same number of types of frequencies as the number of transmitters are not needed. So long as there are four types (frequencies a, b, c, and d), it can be ensured that the frequencies of adjacent bright line patterns are different. This is reasoned by the four color theorem or the four color problem. 
     In detail, in this embodiment, each of the plurality of transmitters changes in luminance at any one of at least four types of frequencies, and two or more light emitters of the plurality of transmitters change in luminance at the same frequency. Moreover, the plurality of transmitters each change in luminance so that the luminance change frequency is different between all transmitters (bright line patterns as transmitter images) which, in the case where the plurality of transmitters are projected on the light receiving surface of the image sensor of the receiver, are adjacent to each other on the light receiving surface. 
       FIG. 443  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     A transmitter changes in luminance by outputting high-luminance light (H) or low-luminance light (L) per predetermined time unit (slot), thereby transmitting a signal. Here, the transmitter transmits a signal for each block made up of a header and a body. The header is expressed as (L, H, L, H, L, H, H) using seven slots, as illustrated in  FIG. 407A  as an example. The body is made up of a plurality of symbols (00, 01, 10, or 11), where each symbol is expressed using four slots (4-value PPM). The block is expressed using a predetermined number (19 in the example in  FIG. 443 ) of slots. For instance, an ID is obtained by combining the body included in each of four blocks. The block may instead be expressed using 33 slots. 
     A bright line pattern obtained by image capture by a receiver includes a pattern (header pattern) corresponding to the header and a pattern (data pattern) corresponding to the body. The data pattern does not include the same pattern as the header pattern. Accordingly, the receiver can easily find the header pattern from the bright line pattern, and measure the number of pixels between the header pattern and the next header pattern (the number of exposure lines corresponding to the block). Since the number of slots per block (19 in the example in  FIG. 43 ) is set to a fixed number regardless of the frequency, the receiver can specify the frequency (the inverse of the duration of one slot) of the transmitter according to the measured number of pixels. That is, the receiver specifies a lower frequency when the number of pixels is larger, and a higher frequency when the number of pixels is smaller. 
     Thus, by capturing the transmitter, the receiver can obtain the ID of the transmitter, and also specify the frequency of the transmitter. Through the use of the specified frequency, the receiver can determine whether or not the obtained ID is correct, that is, perform error detection on the ID. In detail, the receiver calculates a hash value for the ID, and compares the hash value with the specified frequency. In the case where the hash value and the frequency match, the receiver determines that the obtained ID is correct. In the case where the hash value and the frequency do not match, the receiver determines that the obtained ID is incorrect (error). For instance, the receiver uses the remainder when dividing the ID by a predetermined divisor, as the hash value. Conversely, the transmitter transmits the ID, by changing in luminance at the frequency (the inverse of the duration of one slot) of the same value as the hash value for the ID. 
       FIG. 444  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
     The transmitter may change in luminance using an arbitrary frequency, instead of using the frequency of the same value as the hash value as mentioned above. In this case, the transmitter transmits a signal indicating a value different from the ID of the transmitter. For example, in the case where the ID of the transmitter is “100” and the transmitter uses 2 kHz as an arbitrary frequency, the transmitter transmits the signal “1002” that combines the ID and the frequency. Likewise, in the case where the ID of another transmitter is “110” and this other transmitter uses 1 kHz as an arbitrary frequency, the other transmitter transmits the signal “1101” that combines the ID and the frequency. 
     In such a case, the receiver uses the value of the last digit of the signal obtained from the transmitter for error detection, and extracts the value of the other digits as the ID of the transmitter. The receiver compares the frequency specified from the luminance pattern and the value of the last digit of the obtained signal. In the case where the value of the last digit and the frequency match, the receiver determines that the extracted ID is correct. In the case where the value of the last digit and the frequency do not match, the receiver determines that the extracted ID is incorrect (error). 
     In this way, the degree of freedom in setting the luminance change frequency in the transmitter can be increased, while enabling error detection in the receiver. 
       FIG. 445  is a diagram illustrating an example of operation of a receiver in Embodiment 17. 
     As illustrated in  FIG. 445 , there is the case where, in an image obtained by image capture (visible light imaging) by the receiver, a part of a bright line pattern  8327   a  and a part of a bright line pattern  8327   b  overlap each other. In such a case, the receiver does not demodulate data from an overlapping part  8327   c  of the bright line patterns  8327   a  and  8327   b , and demodulates data from the parts of the bright line patterns  8327   a  and  8327   b  other than the part  8327   c . By doing so, the receiver can obtain an appropriate ID from each of the bright line patterns  8327   a  and  8327   b.    
       FIG. 446  is a diagram illustrating an example of operation of a receiver in Embodiment 17. 
     The transmitter switches, for each block as an example, the luminance change frequency for transmitting the block, as illustrated in (a) in  FIG. 433 . This enables the receiver to detect the block boundary more easily. 
     Moreover, the transmitter uses different frequencies as the luminance change frequency for transmitting the header of the block and the luminance change frequency for transmitting the body of the block as an example, as illustrated in (b) in  FIG. 433 . This prevents the same pattern as the header from occurring in the body. As a result, the receiver can distinguish between the header and the body more appropriately. 
       FIG. 447  is a diagram illustrating an example of operation of a system including a transmitter, a receiver, and a server in Embodiment 17. 
     The system in this embodiment includes a transmitter  8331 , a receiver  8332 , and a server  8333 . The transmitter  8331  has the same function as the transmitter in any of Embodiments 1 to 16 described above, and is a lighting device that transmits the ID of the transmitter  8331  by changing in luminance (visible light communication). The receiver  8332  has the same function as the receiver in any of Embodiments 1 to 16 described above, and obtains the ID of the transmitter  8331  from the transmitter  8331  by capturing the transmitter  8331  (visible light imaging). The server  8333  communicates with the transmitter  8331  and the receiver  8332  via a network such as the Internet. 
     Note that, in this embodiment, the ID of the transmitter  8331  is fixed without a change. Meanwhile, the frequency used for the luminance change (visible light communication) of the transmitter  8331  can be arbitrarily changed by setting. 
     In such a system, first the transmitter  8331  registers the frequency used for the luminance change (visible light communication), in the server  8333 . In detail, the transmitter  8331  transmits the ID of the transmitter  8331 , registered frequency information indicating the frequency of the transmitter  8331 , and related information relating to the transmitter  8331 , to the server  8333 . Upon receiving the ID, registered frequency information, and related information of the transmitter  8331 , the server  8333  records them in association with each other. That is, the ID of the transmitter  8331 , the frequency used for the luminance change of the transmitter  8331 , and the related information are recorded in association with each other. The frequency used for the luminance change of the transmitter  8331  is registered in this way. 
     Next, the transmitter  8331  transmits the ID of the transmitter  8331 , by changing in luminance at the registered frequency. The receiver  8332  captures the transmitter  8331  to obtain the ID of the transmitter  8331 , and specifies the luminance change frequency of the transmitter  8331  as mentioned above. 
     The receiver  8332  then transmits the obtained ID and specified frequency information indicating the specified frequency, to the server  8333 . Upon receiving the ID and the specified frequency information transmitted from the receiver  8332 , the server  8333  searches for the frequency (the frequency indicated by the registered frequency information) recorded in association with the ID, and determines whether or not the recorded frequency and the frequency indicated by the specified frequency information match. In the case of determining that the frequencies match, the server  8333  transmits the related information (data) recorded in association with the ID and the frequency, to the receiver  8332 . 
     If the frequency specified by the receiver  8332  does not match the frequency registered in the server  8333 , the related information is not transmitted from the server  8333  to the receiver  8332 . Therefore, by changing the frequency registered in the server  8333  according to need, it is possible to prevent a situation where, once the receiver  8332  has obtained the ID from the transmitter  8331 , the receiver  8332  can receive the related information from the server  8333  at any time. In detail, by changing the frequency registered in the server  8333  (i.e. the frequency used for the luminance change), the transmitter  8331  can prohibit the receiver  8332  that has obtained the ID before the change, from obtaining the related information. In other words, by changing the frequency, it is possible to set a time limit for the obtainment of the related information. As an example, in the case where the user of the receiver  8332  stays at a hotel in which the transmitter  8331  is installed, an administrator in the hotel changes the frequency after the stay. Hence, the receiver  8332  can obtain the related information only on the date when the user stays at the hotel, and is prohibited from obtaining the related information after the stay. 
     The server  8333  may register a plurality of frequencies in association with one ID. For instance, each time the server  8333  receives the registered frequency information from the receiver  8332 , the server  8333  registers the frequencies indicated by four latest sets of registered frequency information, in association with the ID. This allows even the receiver  8332  which obtained the ID in the past, to obtain the related information from the server  8333  until the frequency is changed three times. The server  8333  may also manage, for each registered frequency, the time at which or period during which the frequency is set in the transmitter  8331 . In such a case, upon receiving the ID and the specified frequency information from the receiver  8332 , the server  8333  can specify the period during which the receiver  8332  obtains the ID, by referring to the time period and the like managed for the frequency indicated by the specified frequency information. 
       FIG. 448  is a block diagram illustrating a structure of a transmitter in Embodiment 17. 
     A transmitter  8334  has the same function as the transmitter in any of Embodiments 1 to 16 described above, and includes a frequency storage unit  8335 , an ID storage unit  8336 , a check value storage unit  8337 , a check value comparison unit  8338 , a check value calculation unit  8339 , a frequency calculation unit  8340 , a frequency comparison unit  8341 , a transmission unit  8342 , and an error reporting unit  8343 . 
     The frequency storage unit  8335  stores the frequency used for the luminance change (visible light communication). The ID storage unit  8336  stores the ID of the transmitter  8334 . The check value storage unit  8337  stores a check value for determining whether or not the ID stored in the ID storage unit  8336  is correct. 
     The check value calculation unit  8339  reads the ID stored in the ID storage unit  8336 , and applies a predetermined function to the ID to calculate a check value (calculated check value) for the ID. The check value comparison unit  8338  reads the check value stored in the check value storage unit  8337 , and compares the check value with the calculated check value calculated by the check value calculation unit  8339 . In the case of determining that the calculated check value is different from the check value, the check value comparison unit  8338  notifies an error to the error reporting unit  8343 . For example, the check value storage unit  8337  stores the value “0” indicating that the ID stored in the ID storage unit  8336  is an even number, as the check value. The check value calculation unit  8339  reads the ID stored in the ID storage unit  8336 , and divides it by the value “2” to calculate the remainder as the calculated check value. The check value comparison unit  8338  compares the check value “0” and the calculated check value which is the remainder of the division mentioned above. 
     The frequency calculation unit  8340  reads the ID stored in the ID storage unit  8336  via the check value calculation unit  8339 , and calculates the frequency (calculated frequency) from the ID. For instance, the frequency calculation unit  8340  divides the ID by a predetermined value, to calculate the remainder as the frequency. The frequency comparison unit  8341  compares the frequency (stored frequency) stored in the frequency storage unit  8335  and the calculated frequency. In the case of determining that the calculated frequency is different from the stored frequency, the frequency comparison unit  8341  notifies an error to the error reporting unit  8343 . 
     The transmission unit  8342  transmits the ID stored in the ID storage unit  8336 , by changing in luminance at the calculated frequency calculated by the frequency calculation unit  8340 . 
     The error reporting unit  8343 , when notified of the error from at least one of the check value comparison unit  8338  and the frequency comparison unit  8341 , reports the error by buzzer sound, blink, or lighting. In detail, the error reporting unit  8343  includes a lamp for error reporting, and reports the error by lighting or blinking the lamp. Alternatively, when the power switch of the transmitter  8334  is turned on, the error reporting unit  8343  reports the error by blinking, at a frequency perceivable by humans, a light source that changes in luminance to transmit a signal such as an ID, for a predetermined period (e.g. 10 seconds). 
     Thus, whether or not the ID stored in the ID storage unit  8336  and the frequency calculated from the ID are correct is checked, with it being possible to prevent erroneous ID transmission and luminance change at an erroneous frequency. 
       FIG. 449  is a block diagram illustrating a structure of a receiver in Embodiment 17. 
     A receiver  8344  has the same function as the receiver in any of Embodiments 1 to 16 described above, and includes a light receiving unit  8345 , a frequency detection unit  8346 , an ID detection unit  8347 , a frequency comparison unit  3848 , and a frequency calculation unit  8349 . 
     The light receiving unit  8345  includes an image sensor as an example, and captures (visible light imaging) a transmitter that changes in luminance to obtain an image including a bright line pattern. The ID detection unit  8347  detects the ID of the transmitter from the image. That is, the ID detection unit  8347  obtains the ID of the transmitter, by demodulating data specified by the bright line pattern included in the image. The frequency detection unit  8346  detects the luminance change frequency of the transmitter, from the image. That is, the frequency detection unit  8346  specifies the frequency of the transmitter from the bright line pattern included in the image, as in the example described with reference to  FIG. 443 . 
     The frequency calculation unit  8349  calculates the frequency of the transmitter from the ID detected by the ID detection unit  8347 , for example by dividing the ID as mentioned above. The frequency comparison unit  8348  compares the frequency detected by the frequency detection unit  8346  and the frequency calculated by the frequency calculation unit  8349 . In the case where these frequencies are different, the frequency comparison unit  8348  determines that the detected ID is an error, and causes the ID detection unit  8347  to detect the ID again. Obtainment of an erroneous ID can be prevented in this way. 
       FIG. 450  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     The transmitter may transmit each of the symbols “00, 01, 10, 10” separately, by making the luminance change position in a predetermined time unit different. 
     For example, when transmitting the symbol “00”, the transmitter transmits the symbol “00” by changing in luminance only for a first section which is the first section in the time unit. When transmitting the symbol “01”, the transmitter transmits the symbol “01” by changing in luminance only for a second section which is the second section in the time unit. Likewise, when transmitting the symbol “10”, the transmitter transmits the symbol “10” by changing in luminance only for a third section which is the third section in the time unit. When transmitting the symbol “11”, the transmitter transmits the symbol “11” by changing in luminance only for a fourth section which is the fourth section in the time unit. 
     Thus, in this embodiment, the luminance changes in one section regardless of which symbol is transmitted, so that flicker can be suppressed as compared with the above-mentioned transmitter that causes one entire section (slot) to be low in luminance. 
       FIG. 451  is a diagram illustrating an example of a transmitter in Embodiment 17. 
     The transmitter may transmit each of the symbols “0, 1” separately, by making whether or not the luminance changes in a predetermined time unit different. For example, when transmitting the symbol “0”, the transmitter transmits the symbol “0” by not changing in luminance in the time unit. When transmitting the symbol “1”, the transmitter transmits the symbol “1” by changing in luminance in the time unit. 
       FIG. 452  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     The transmitter may transmit each of the symbols “00, 01, 10, 10” separately, by making the luminance change frequency in a predetermined time unit different. For example, when transmitting the symbol “00”, the transmitter transmits the symbol “00” by not changing in luminance in the time unit. When transmitting the symbol “01”, the transmitter transmits the symbol “01” by changing in luminance (changing in luminance at a low frequency) in the time unit. When transmitting the symbol “10”, the transmitter transmits the symbol “10” by changing in luminance sharply (changing in luminance at a high frequency) in the time unit. When transmitting the symbol “11”, the transmitter transmits the symbol “11” by changing in luminance more sharply (changing in luminance at a higher frequency) in the time unit. 
       FIG. 453  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     The transmitter may transmit each of the symbols “0, 1” separately, by making the phase of the luminance change in a predetermined time unit different. For example, when transmitting the symbol “0”, the transmitter transmits the symbol “0” by changing in luminance in a predetermined phase in the time unit. When transmitting the symbol “1”, the transmitter transmits the symbol “1” by changing in luminance in the reverse phase of the above-mentioned phase in the time unit. 
       FIG. 454  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     When transmitting a signal such as an ID, the transmitter changes in luminance according to color such as red, green and blue. The transmitter can therefore transmit a signal of a larger amount of information, to a receiver capable of recognizing the luminance change according to color. The luminance change of any of the colors may be used for clock synchronization. For example, the luminance change of red color may be used for clock synchronization. In this case, the luminance change of red color serves as a header. Since there is no need to use a header for the luminance change of each color (green and blue) other than red, redundant data transmission can be avoided. 
       FIG. 455  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     The transmitter may express the luminance of synthetic color (e.g. white) by synthesizing a plurality of colors such as red, green, and blue. In other words, the transmitter expresses the luminance change of synthetic color, by changing in luminance according to color such as red, green, and blue. A signal is transmitted using this luminance change of synthetic color, as in the above-mentioned visible light communication. Here, the luminance of one or more colors of red, green, and blue may be used for adjustment when expressing predetermined luminance of synthetic color. This enables the signal to be transmitted using the luminance change of synthetic color, and also enables the signal to be transmitted using the luminance change of any two colors of red, green, and blue. The transmitter can therefore transmit a signal even to a receiver capable of recognizing only the luminance change of the above-mentioned synthetic color (e.g. white), and also transmit more signals as ancillary information to a receiver capable of recognizing each color such as red, green, and blue. 
       FIG. 456  is a diagram illustrating an example of operation of a transmitter in Embodiment 17. 
     The transmitter includes four light sources. The four light sources (e.g. LED lights) emit light of the colors expressed by different positions  8351   a ,  8351   b ,  8352   a , and  8352   b  in a CIExy chromaticity diagram illustrated in  FIG. 456 . 
     The transmitter transmits each signal by switching between first lighting transmission and second lighting transmission. The first lighting transmission is a process of transmitting the signal “0” by turning on the light source for emitting light of the color of the position  8351   a  and the light source for emitting the light of the color of the position  8351   b  from among the four light sources. The second lighting transmission is a process of transmitting the signal “1” by turning on the light source for emitting light of the color of the position  8352   a  and the light source for emitting the light of the color of the position  8352   b . The image sensor in the receiver can identify the color expressed by each of the positions  8351   a ,  8351   b ,  8352   a , and  8352   b , and so the receiver can appropriately receive the signal “0” and the signal “1”. 
     During the first lighting transmission, the color expressed by the intermediate position between the positions  8351   a  and  8351   b  in the CIExy chromaticity diagram is seen by the human eye. Likewise, during the second lighting transmission, the color expressed by the intermediate position between the positions  8352   a  and  8352   b  in the CIExy chromaticity diagram is seen by the human eye. Therefore, by appropriately adjusting the color and luminance of each of the four light sources, it is possible to match the intermediate position between the positions  8351   a  and  8351   b  and the intermediate position between the positions  8352   a  and  8352   b  to each other (to a position  8353 ). As a result, even when the transmitter switches between the first lighting transmission and the second lighting transmission, to the human eye the light emission color of the transmitter appears to be fixed. Flicker perceived by humans can thus be suppressed. 
       FIG. 457  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
     The transmitter includes an ID storage unit  8361 , a random number generation unit  8362 , an addition unit  8363 , an encryption unit  8364 , and a transmission unit  8365 . The ID storage unit  8361  stores the ID of the transmitter. The random number generation unit  8362  generates a different random number at regular time intervals. The addition unit  8363  combines the ID stored in the ID storage unit  8361  with the latest random number generated by the random number generation unit  8362 , and outputs the result as an edited ID. The encryption unit  8364  encrypts the edited ID to generate an encrypted edited ID. The transmission unit  8365  transmits the encrypted edited ID to the receiver by changing in luminance. 
     The receiver includes a reception unit  8366 , a decryption unit  8367 , and an ID obtainment unit  8368 . The reception unit  8366  receives the encrypted edited ID from the transmitter, by capturing the transmitter (visible light imaging). The decryption unit  8367  decrypts the received encrypted edited ID to restore the edited ID. The ID obtainment unit  8368  extracts the ID from the edited ID, thus obtaining the ID. 
     For instance, the ID storage unit  8361  stores the ID “100”, and the random number generation unit  8362  generates a new random number “817” (example 1). In this case, the addition unit  8363  combines the ID “100” with the random number “817” to generate the edited ID “100817”, and outputs it. The encryption unit  8364  encrypts the edited ID “100817” to generate the encrypted edited ID “abced”. The decryption unit  8367  in the receiver decrypts the encrypted edited ID “abced” to restore the edited ID “100817”. The ID obtainment unit  8368  extracts the ID “100” from the restored edited ID “100817”. In other words, the ID obtainment unit  8368  obtains the ID “100” by deleting the last three digits of the edited ID. 
     Next, the random number generation unit  8362  generates a new random number “619” (example 2). In this case, the addition unit  8363  combines the ID “100” with the random number “619” to generate the edited ID “100619”, and outputs it. The encryption unit  8364  encrypts the edited ID “100619” to generate the encrypted edited ID “difia”. The decryption unit  8367  in the receiver decrypts the encrypted edited ID “difia” to restore the edited ID “100619”. The ID obtainment unit  8368  extracts the ID “100” from the restored edited ID “100619”. In other words, the ID obtainment unit  8368  obtains the ID “100” by deleting the last three digits of the edited ID. 
     Thus, the transmitter does not simply encrypt the ID but encrypts its combination with the random number changed at regular time intervals, with it being possible to prevent the ID from being easily cracked from the signal transmitted from the transmission unit  8365 . That is, in the case where the simply encrypted ID is transmitted from the transmitter to the receiver a plurality of times, even though the ID is encrypted, the signal transmitted from the transmitter to the receiver is the same if the ID is the same, so that there is a possibility of the ID being cracked. In the example illustrated in  FIG. 457 , however, the ID is combined with the random number changed at regular time intervals, and the ID combined with the random number is encrypted. Therefore, even in the case where the same ID is transmitted to the receiver a plurality of times, if the time of transmitting the ID is different, the signal transmitted from the transmitter to the receiver is different. This protects the ID from being cracked easily. 
       FIG. 458  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
     The transmitter includes an ID storage unit  8371 , a timer unit  8372 , an addition unit  8373 , an encryption unit  8374 , and a transmission unit  8375 . The ID storage unit  8371  stores the ID of the transmitter. The timer unit  8372  counts time, and outputs the current date and time (the current year, month, day, and time). The addition unit  8373  combines the ID stored in the ID storage unit  8371  with the current date and time output from the timer unit  8372  as a transmission date and time, and outputs the result as an edited ID. The encryption unit  8374  encrypts the edited ID to generate an encrypted edited ID. The transmission unit  8375  transmits the encrypted edited ID to the receiver by changing in luminance. 
     The receiver includes a reception unit  8376 , a decryption unit  8377 , a validity determination unit  8378 , and a timer unit  8379 . The reception unit  8376  receives the encrypted edited ID from the transmitter, by capturing the transmitter (visible light imaging). The decryption unit  8377  decrypts the received encrypted edited ID to restore the edited ID. The timer unit  8379  counts time, and outputs the current date and time (the current year, month, day, and time). The validity determination unit  8378  extracts the ID from the restored edited ID, thus obtaining the ID. The validity determination unit  8378  also extracts the transmission date and time from the restored edited ID, and compares the transmission date and time with the current date and time output from the timer unit  8379  to determine the validity of the ID. For example, in the case where the difference between the transmission date and time and the current date and time is longer than a predetermined time or in the case where the transmission date and time is later than the current date and time, the validity determination unit  8378  determines that the ID is invalid. 
     For instance, the ID storage unit  8371  stores the ID “100”, and the timer unit  8372  outputs the current date and time “201305011200” (2013 May 1 12:00) as the transmission date and time (example 1). In this case, the addition unit  8373  combines the ID “100” with the transmission date and time “201305011200” to generate the edited ID “100201305011200”, and outputs it. The encryption unit  8374  encrypts the edited ID “100201305011200” to generate the encrypted edited ID “ei39ks”. The decryption unit  8377  in the receiver decrypts the encrypted edited ID “ei39ks” to restore the edited ID “100201305011200”. The validity determination unit  8378  extracts the ID “100” from the restored edited ID “100201305011200”. In other words, the validity determination unit  8378  obtains the ID “100” by deleting the last 12 digits of the edited ID. The validity determination unit  8378  also extracts the transmission date and time “201305011200” from the restored edited ID “100201305011200”. If the transmission date and time “201305011200” is earlier than the current date and time output from the timer unit  8379  and the difference between the transmission date and time and the current date and time is within, for example, 10 minutes, the validity determination unit  8378  determines that the ID “100” is valid. 
     On the other hand, the ID storage unit  8371  stores the ID “100”, and the timer unit  8372  outputs the current date and time “201401011730” (2014 Jan. 1 17:30) as the transmission date and time (example 2). In this case, the addition unit  8373  combines the ID “100” with the transmission date and time “201401011730” to generate the edited ID “100201401011730”, and outputs it. The encryption unit  8374  encrypts the edited ID “100201401011730” to generate the encrypted edited ID “002jflk”. The decryption unit  8377  in the receiver decrypts the encrypted edited ID “002jflk” to restore the edited ID “100201401011730”. The validity determination unit  8378  extracts the ID “100” from the restored edited ID “100201401011730”. In other words, the validity determination unit  8378  obtains the ID “100” by deleting the last 12 digits of the edited ID. The validity determination unit  8378  also extracts the transmission date and time “201401011730” from the restored edited ID “100201401011730”. If the transmission date and time “201401011730” is later than the current date and time output from the timer unit  8379 , the validity determination unit  8378  determines that the ID “100” is invalid. 
     Thus, the transmitter does not simply encrypt the ID but encrypts its combination with the current date and time changed at regular time intervals, with it being possible to prevent the ID from being easily cracked from the signal transmitted from the transmission unit  8375 . That is, in the case where the simply encrypted ID is transmitted from the transmitter to the receiver a plurality of times, even though the ID is encrypted, the signal transmitted from the transmitter to the receiver is the same if the ID is the same, so that there is a possibility of the ID being cracked. In the example illustrated in  FIG. 458 , however, the ID is combined with the current date and time changed at regular time intervals, and the ID combined with the current date and time is encrypted. Therefore, even in the case where the same ID is transmitted to the receiver a plurality of times, if the time of transmitting the ID is different, the signal transmitted from the transmitter to the receiver is different. This protects the ID from being cracked easily. 
     Moreover, whether or not the obtained ID is valid is determined by comparing the transmission date and time of the encrypted edited ID and the current date and time. Thus, the validity of the ID can be managed based on the transmission/reception time. 
     Note that the receiver illustrated in each of  FIGS. 457 and 458  may, upon obtaining the encrypted edited ID, transmit the encrypted edited ID to the server, and obtain the ID from the server. 
     (Station Guide) 
       FIG. 459  is a diagram illustrating an example of use according to the present disclosure on a train platform. A user points a mobile terminal at an electronic display board or a lighting, and obtains information displayed on the electronic display board or train information or station information of a station where the electronic display board is installed, by visible light communication. Here, the information displayed on the electronic display board may be directly transmitted to the mobile terminal by visible light communication, or ID information corresponding to the electronic display board may be transmitted to the mobile terminal so that the mobile terminal inquires of a server using the obtained ID information to obtain the information displayed on the electronic display board. In the case where the ID information is transmitted from the mobile terminal, the server transmits the information displayed on the electronic display board to the mobile terminal, based on the ID information. Train ticket information stored in a memory of the mobile terminal is compared with the information displayed on the electronic display board and, in the case where ticket information corresponding to the ticket of the user is displayed on the electronic display board, an arrow indicating the way to the platform at which the train the user is going to ride arrives is displayed on a display of the mobile terminal. An exit or a path to a train car near a transfer route may be displayed when the user gets off a train. When a seat is reserved, a path to the seat may be displayed. When displaying the arrow, the same color as the train line in a map or train guide information may be used to display the arrow, to facilitate understanding. Reservation information (platform number, car number, departure time, seat number) of the user may be displayed together with the arrow. A recognition error can be prevented by also displaying the reservation information of the user. In the case where the ticket is stored in a server, the mobile terminal inquires of the server to obtain the ticket information and compares it with the information displayed on the electronic display board, or the server compares the ticket information with the information displayed on the electronic display board. Information relating to the ticket information can be obtained in this way. The intended train line may be estimated from a history of transfer search made by the user, to display the route. Not only the information displayed on the electronic display board but also the train information or station information of the station where the electronic display board is installed may be obtained and used for comparison. Information relating to the user in the electronic display board displayed on the display may be highlighted or modified. In the case where the train ride schedule of the user is unknown, a guide arrow to each train line platform may be displayed. When the station information is obtained, a guide arrow to souvenir shops and toilets may be displayed on the display. The behavior characteristics of the user may be managed in the server so that, in the case where the user frequently goes to souvenir shops or toilets in a train station, the guide arrow to souvenir shops and toilets is displayed on the display. By displaying the guide arrow to souvenir shops and toilets only to each user having the behavior characteristics of going to souvenir shops or toilets while not displaying the guide arrow to other users, it is possible to reduce processing. The guide arrow to souvenir shops and toilets may be displayed in a different color from the guide arrow to the platform. When displaying both arrows simultaneously, a recognition error can be prevented by displaying them in different colors. Though a train example is illustrated in  FIG. 459 , the same structure is applicable to display for planes, buses, and so on. 
     (Guide Sign Translation) 
       FIG. 460  is a diagram illustrating an example of obtaining information from an electronic guidance display board installed in an airport, a train station, a hospital, or the like by visible light communication. Information displayed on the electronic guidance display board is obtained by visible light communication and, after the displayed information is translated into language information set in a mobile terminal, the information is displayed on a display of the mobile terminal. Since the displayed information has been translated into the language of the user, the user can easily understand the information. The language translation may be performed in the mobile terminal or in a server. In the case of performing the translation in the server, the mobile terminal may transmit the displayed information obtained by visible light communication and the language information of the mobile terminal to the server. The server then performs the translation and transmits the translated information to the mobile terminal, and the mobile terminal displays the information on the display. In the case of obtaining ID information from the electronic guidance display board, the mobile terminal may transmit ID information to the server, and obtain display information corresponding to the ID information from the server. Furthermore, a guide arrow indicating where the user should go next may be displayed based on nationality information, ticket information, or baggage check information stored in the mobile terminal. 
     (Coupon Popup) 
       FIG. 461  is a diagram illustrating an example of displaying, on a display of a mobile terminal, coupon information obtained by visible light communication or a popup when a user comes close to a store. The user obtains the coupon information of the store from an electronic display board or the like by visible light communication, using his or her mobile terminal. After this, when the user enters a predetermined range from the store, the coupon information of the store or a popup is displayed. Whether or not the user enters the predetermined range from the store is determined using GPS information of the mobile terminal and store information included in the coupon information. The information is not limited to coupon information, and may be ticket information. Since the user is automatically alerted when coming close to a store where a coupon or a ticket can be used, the user can use the coupon or the ticket effectively. 
       FIG. 462  is a diagram illustrating an example of displaying coupon information, ticket information, or a popup on a display of a mobile terminal at a cash register, a ticket gate, or the like. Position information is obtained from a lighting installed at the cash register or the ticket gate, by visible light communication. In the case where the obtained position information matches information included in the coupon information or the ticket information, the display is performed. A barcode reader may include a light emitting unit so that the position information is obtained by performing visible light communication with the light emitting unit. Alternatively, the position information may be obtained from the GPS of the mobile terminal. A transmitter may be installed near the cash register so that, when the user points the receiver at the transmitter, the coupon or payment information is displayed on the display of the receiver. The receiver may also perform the payment process by communicating with the server. The coupon information or the ticket information may include Wi-Fi information installed in a store or the like so that, in the case where the mobile terminal of the user obtains the same information as the W-Fi information included in the coupon information or the ticket information, the display is performed. 
     (Start of Operation Application) 
       FIG. 463  is a diagram illustrating an example where a user obtains information from a home appliance by visible light communication using a mobile terminal. In the case where ID information or information related to the home appliance is obtained from the home appliance by visible light communication, an application for operating the home appliance starts automatically.  FIG. 463  illustrates an example of using a TV. Thus, merely pointing the mobile terminal at the home appliance enables the application for operating the home appliance to start. 
     (Stopping Transmission During Operation of Barcode Reader) 
       FIG. 464  is a diagram illustrating an example of stopping, when a barcode reader  8405   a  reads a barcode of a product, data communication for visible light communication is stopped near the barcode reader  8405   a . By stopping visible light communication during barcode read, the barcode reader  8405   a  can be kept from erroneously recognizing the barcode. When a barcode read button is pressed, the barcode reader  8405   a  transmits a transmission stop signal to a visible light signal transmitter  8405   b . When the finger is released from the button or when a predetermined time has elapsed after the release, the barcode reader  8405   a  transmits a transmission restart signal to the visible light signal transmitter  8405   b . The transmission stop signal or the transmission restart signal is transmitted by wired/wireless communication, infrared communication, or sound wave communication. The barcode reader  8405   a  may transmit the transmission stop signal upon estimating that the barcode reader  8405   a  is moved, and transmit the transmission restart signal upon estimating that the barcode reader  8405   a  is not moved for a predetermined time, based on the measurement of an accelerometer included in the barcode reader  8405   a . The barcode reader  8405   a  may transmit the transmission stop signal upon estimating that the barcode reader  8405   a  is grasped, and transmit the transmission restart signal upon estimating that the hand is released from the barcode reader  8405   a , based on the measurement of an electrostatic sensor or an illuminance sensor included in the barcode reader  8405   a . The barcode reader  8405   a  may transmit the transmission stop signal upon detecting that the barcode reader  8405   a  is lifted on the ground that a switch on the supporting surface of the barcode reader  8405   a  is released form the pressed state, and transmit the transmission restart signal upon detecting that the barcode reader  8405   a  is placed on the ground that the button is pressed. The barcode reader  8405   a  may transmit the transmission stop signal upon detecting that the barcode reader  8405   a  is lifted, and transmit the transmission restart signal upon detecting that the barcode reader  8405   a  is placed again, based on the measurement of a switch or an infrared sensor of a barcode reader receptacle. A cash register  8405   c  may transmit the transmission stop signal when operation is started, and transmit the transmission restart signal when settlement is completed. 
     Upon receiving the transmission stop signal, the transmitter  8405   b  such as a lighting stops signal transmission, or operates so that the ripple (luminance change) from 100 Hz to 100 kHz is smaller. As an alternative, the transmitter  8405   b  continues signal transmission while reducing the luminance change of the signal pattern. As another alternative, the transmitter  8405   b  makes the carrier wave period longer than the barcode read time of the barcode reader  8405   a , or makes the carrier wave period shorter than the exposure time of the barcode reader  8405   a . Malfunction of the barcode reader  8405   b  can be prevented in this way. 
     As illustrated in  FIG. 465 , a transmitter  8406   b  such as a lighting detects, by a motion sensor or a camera, that there is a person near a barcode reader  8406   a , and stops signal transmission. As an alternative, the transmitter  8406   b  performs the same operation as the transmitter  8405   b  when receiving the transmission stop signal. The transmitter  8406   b  restarts signal transmission, upon detecting that no one is present near the barcode reader  8406   a  any longer. The transmitter  8406   b  may detect the operation sound of the barcode reader  8406   a , and stop signal transmission for a predetermined time. 
     (Information Transmission from Personal Computer) 
       FIG. 466  is a diagram illustrating an example of use according to the present disclosure. 
     A transmitter  8407   a  such as a personal computer transmits a visible light signal, through a display device such as a display included in the transmitter  8407   a , a display connected to the transmitter  8407   a , or a projector. The transmitter  8407   a  transmits an URL of a website displayed by a browser, information of a clipboard, or information defined by a focused application. For example, the transmitter  8407   a  transmits coupon information obtained in a website. 
     (Database) 
       FIG. 467  is a diagram illustrating an example of a structure of a database held in a server that manages an ID transmitted from a transmitter. 
     The database includes an ID-data table holding data provided in response to an inquiry using an ID as a key, and an access log table holding each record of inquiry using an ID as a key. The ID-data table includes an ID transmitted from a transmitter, data provided in response to an inquiry using the ID as a key, a data provision condition, the number of times access is made using the ID as a key, and the number of times the data is provided as a result of clearing the condition. Examples of the data provision condition include the date and time, the number of accesses, the number of successful accesses, terminal information of the inquirer (terminal model, application making inquiry, current position of terminal, etc.), and user information of the inquirer (age, sex, occupation, nationality, language, religion, etc.). By using the number of successful accesses as the condition, a method of providing such a service that “1 yen per access, though no data is returned after 100 yen as upper limit” is possible. When access is made using an ID as a key, the log table records the ID, the user ID of the requester, the time, other ancillary information, whether or not data is provided as a result of clearing the condition, and the provided data. 
     (Reception Start Gesture) 
       FIG. 468  is a diagram illustrating an example of gesture operation for starting reception by the present communication scheme. 
     A user sticks out a receiver such as a smartphone and turns his or her wrist right and left, to start reception. The receiver detects these operations from the measurement of a 9-axis sensor, and starts reception. The receiver may start reception in the case of detecting at least one of these operations. The operation of sticking out the receiver has the effect of enhancing the reception speed and accuracy, because the receiver comes closer to a transmitter and so captures the transmitter in a larger size. The operation of turning the wrist right and left has the effect of stabilizing reception, because the angle dependence of the scheme is resolved by changing the angle of the receiver. 
     Note that these operations may be performed only when the receiver&#39;s home screen is in the foreground. This can prevent the communication from being launched despite the user&#39;s intension while the user is using another application. 
     The following modification is also possible: an image sensor is activated upon detection of the operation of sticking out the receiver and, if the operation of turning the wrist right and left is not conducted, the reception is canceled. Since activating the image sensor takes about several hundred milliseconds to 2 seconds, the responsiveness can be enhanced in this way. 
     (Control of Transmitter by Power Line) 
       FIG. 469  is a diagram illustrating an example of a transmitter according to the present disclosure. 
     A signal control unit  8410   g  controls the transmission state (the contents of a transmission signal, whether or not to transmit the signal, the intensity of luminance change used for transmission, etc.) of a transmitter  8410   a . The signal control unit  8410   g  transmits the details of control of the transmitter  8410   a , to a power distribution control unit  8410   f . The power distribution control unit  8410   f  changes the voltage or current supplied to a power supply unit  8410   b  of the transmitter  8410   a  or its frequency, thereby notifying the details of control in the form of the magnitude of the change or the time of the change. The power supply unit  8410   b  produces constant output, without being affected by a slight change in voltage, current, or frequency. Accordingly, the signal is transmitted by being expressed by such a change that exceeds the stabilizing ability of the power supply unit  8410   b , e.g. a timing or duration that cuts power supply. A luminance control unit  8410   d  receives the signal transmitted from the power distribution control unit  8410   f  while taking into account the conversion by the power supply unit  8410   b , and changes the luminance change pattern of a light emitting unit. 
     (Coding Scheme) 
       FIG. 470  is a diagram illustrating a coding scheme for a visible light communication image. 
     This coding scheme has the advantage that flicker is unlikely to be perceived by humans, because black and white are substantially equal in proportion and so the normal phase image and the reverse phase image are substantially equal in average luminance. 
     (Coding Scheme Capable of Light Reception Even in the Case of Capturing Image from Diagonal Direction) 
       FIG. 471  is a diagram illustrating a coding scheme for a visible light communication image. 
     An image  1001   a  is an image displayed with black and white lines of uniform width. In an image  1001   b  obtained by capturing the image  1001   a  from a diagonal direction, left lines appear thinner and right lines appear thicker. In an image  1001   i  obtained by capturing the image  1001   a  in a manner of projecting the image  1001   a  on a curved surface, lines that differ in thickness appear. 
     In view of this, a visible light communication image is generated by the following coding scheme. A visible light communication image  1001   c  is made up of a white line, a black line whose thickness is three times that of the white line, and a white line whose thickness is ⅓ that of the black line, from left. A preamble is coded as such an image in which a line whose thickness is three times that of its left adjacent line is followed by a line whose thickness is ⅓ that of its left adjacent line. As in visible light communication images  1001   d  and  1001   e , a line whose thickness is equal to that of its left adjacent line is coded as “0”. As in visible light communication images  1001   f  and  1001   g , a line whose thickness is twice that of its left adjacent line or ½ that of its left adjacent line is coded as “1”. That is, a line whose thickness is different from that of its left adjacent line is coded as “1”. As an example using this coding scheme, a signal including “010110001011” following the preamble is expressed by an image such as a visible light communication image  1001   h . Though the line whose thickness is equal to that of its left adjacent line is coded as “0” and the line whose thickness is different from that of its left adjacent line is coded as “1” in this example, the line whose thickness is equal to that of its left adjacent line may be coded as “1” and the line whose thickness is different from that of its left adjacent line as “0”. Moreover, the reference thickness is not limited to the thickness of the left adjacent line, and may be the thickness of the right adjacent line. In detail, “1” or “0” may be coded depending on whether the thickness of the line to be coded is equal to or different from the thickness of its right adjacent line. Thus, a transmitter codes “0” by setting the line to be coded to be equal in thickness to the line that is different in color from and adjacent to the line to be coded, and codes “1” by setting the line to be coded to be different in thickness from the line that is different in color from and adjacent to the line to be coded. 
     A receiver captures the visible light communication image, and detects the thickness of the white or black line in the captured visible light communication image. The receiver compares the thickness of the line to be decoded, with the thickness of the line that is different in color from and adjacent (left adjacent or right adjacent) to the line to be decoded. The line is decoded as “0” in the case where the thicknesses are equal, and “1” in the case where the thicknesses are different. Alternatively, the line may be decoded as “1” in the case where the thicknesses are equal, and “0” in the case where the thicknesses are different. The receiver lastly decodes the data based on the decoded data sequence of 1 and 0. 
     This coding scheme employs the local line thickness relation. Since the thickness ratio between neighboring lines does not change significantly as seen in the images  1001   b  and  1001   i , the visible light communication image generated by this coding scheme can be properly decoded even in the case of being captured from a diagonal direction or being projected on a curved surface. 
     This coding scheme has the advantage that flicker is unlikely to be perceived by humans, because black and white are substantially equal in proportion and so the normal phase image and the reverse phase image are substantially equal in average luminance. This coding scheme also has the advantage that the visible light communication images of both the normal phase signal and the reverse phase signal are decodable by the same algorithm, because the coding scheme does not depend on the distinction between black and white. 
     This coding scheme further has the advantage that a code can be added easily. As an example, a visible light communication image  1001   j  is a combination of a line whose thickness is four times that of its left adjacent line and a line whose thickness is ¼ that of its left adjacent line. Like this, many unique patterns such as “five times that of its left adjacent line and ⅕ that of its left adjacent line” and “three times that of its left adjacent line and ⅔ that of its left adjacent line” are available, enabling definition as a signal having a special meaning. For instance, given that one set of data can be expressed by a plurality of visible light communication images, the visible light communication image  1001   j  may be used as a cancel signal indicating that, since the transmission data is changed, part of the previously received data is no longer valid. Note that the colors are not limited to black and white, and any colors may be used so long as they are different. For instance, complementary colors may be used. 
     (Coding Scheme that Differs in Information Amount Depending on Distance) 
       FIGS. 472 and 473  are diagrams illustrating a coding scheme for a visible light communication image. 
     As in (a- 1 ) in  FIG. 472 , when a 2-bit signal is expressed in a form that one part of an image divided by four is black and the other parts are white, the average luminance of the image is 75%, where white is 100% and black is 0%. As in (a- 2 ) in  FIG. 472 , when black and white are reversed, the average luminance is 25%. 
     An image  1003   a  is a visible light communication image in which the white part of the visible light communication image generated by the coding scheme in  FIG. 471  is expressed by the image in (a- 1 ) in  FIG. 472  and the black part is expressed by the image in (a- 2 ) in  FIG. 472 . This visible light communication image represents signal A coded by the coding scheme in  FIG. 471  and signal B coded by (a- 1 ) and (a- 2 ) in  FIG. 472 . When a nearby receiver  1003   b  captures the visible light communication image  1003   a , a fine image  1003   d  is obtained and both of signals A and B can be received. When a distant receiver  1003   c  captures the visible light communication image  1003   a , a small image  1003   e  is obtained. In the image  1003   e , the details are not recognizable, and the part corresponding to (a- 1 ) in  FIG. 472  is white and the part corresponding to (a- 2 ) in  FIG. 472  is black, so that only signal A can be received. Thus, more information can be transmitted when the distance between the visible light communication image and the receiver is shorter. The scheme for coding signal B may be the combination of (b- 1 ) and (b- 2 ) or the combination of (c- 1 ) and (c- 2 ) in  FIG. 472 . 
     The use of signals A and B enables basic important information to be expressed by signal A and additional information to be expressed by signal B. In the case where the receiver transmits signals A and B to a server as ID information and the server transmits information corresponding to the ID information to the receiver, the information transmitted from the server may be varied depending on whether or not signal B is present. 
     (Coding Scheme with Data Division) 
       FIG. 474  is a diagram illustrating a coding scheme for a visible light communication image. 
     A transmission signal  1005   a  is divided into a plurality of data segments  1005   b ,  1005   c , and  1005   d . Frame data  1005   e ,  1005   f , and  1005   g  are generated by adding, to each data segment, an address indicating the position of the data segment, a preamble, an error detection/correction code, a frame type description, and the like. The frame data are coded to generate visible light communication images  1005   h ,  1005   i , and  1005   j , and the visible light communication images  1005   h ,  1005   i , and  1005   j  are displayed. In the case where the display area is sufficiently large, a visible light communication image  1005   k  obtained by concatenating the plurality of visible light communication images is displayed. 
     (Effect of Inserting Reverse Phase Image) 
       FIGS. 475 and 476  are diagrams illustrating a coding scheme for a visible light communication image. 
     As in ( 1006   a ) in  FIG. 475 , a transmitter inserts a black image between video and a visible light communication image (normal phase image). An image obtained by capturing this by a receiver is as illustrated in ( 1006   b ) in  FIG. 475 . Since it is easy to search for a part where a simultaneously exposed pixel line is all black, the receiver can easily specify the position where the visible light communication image is captured, as the pixel position exposed at the next timing. 
     As in ( 1006   a ) in  FIG. 475 , after displaying a visible light communication image (normal phase image), the transmitter displays a visible light communication image of reverse phase with black and white being inverted. The receiver calculates the difference in pixel value between the normal phase image and the reverse phase image, thus attaining an SN ratio that is twice as compared with the case of using only the normal phase image. Conversely, when ensuring the same SN ratio, the luminance difference between black and white can be reduced to half, with it being possible to suppress flicker perceived by humans. As in ( 1007   a ) and ( 1007   b ) in  FIG. 476 , the moving average of the expected value of the luminance difference between the video and the visible light communication image is canceled out by the normal phase image and the reverse phase image. Since the temporal resolution of human vision is about 1/60 second, by setting the time for displaying the visible light communication image to less than or equal to this, it is possible to make humans perceive as if the visible light communication image is not being displayed. 
     As in ( 1006   c ) in  FIG. 475 , the transmitter may further insert a black image between the normal phase image and the reverse phase image. In this case, an image illustrated in ( 1006   d ) in  FIG. 475  is obtained as a result of image capture by the receiver. In the image illustrated in ( 1006   b ) in  FIG. 475 , the pattern of the normal phase image and the pattern of the reverse phase image are adjacent to each other, which might cause averaging of pixel values at the boundary. In the image illustrated in ( 1006   d ) in  FIG. 475 , no such problem occurs. 
     (Superresolution) 
       FIG. 477  is a diagram illustrating a coding scheme for a visible light communication image. 
     In (a) in  FIG. 477 , in the case where video data and signal data transmitted by visible light communication are separated, a superresolution process is performed on the video data, and the visible light communication image is superimposed on the obtained superresolution image. That is, the superresolution process is not performed on the visible light communication image. In (b) in  FIG. 477 , in the case where a visible light communication image is already superimposed on video data, the superresolution process is performed so that (1) the edges (parts indicating data by the difference between colors such as black and white) of the visible light communication image are maintained sharp and (2) the average image of the normal phase image and the reverse phase image of the visible light communication image is of uniform luminance. By changing the process for the visible light communication image depending on whether or not the visible light communication image is superimposed on the video data in this way, visible light communication can be performed more appropriately (with reduced error rate). 
     (Display of Support for Visible Light Communication) 
       FIG. 478  is a diagram illustrating operation of a transmitter. 
     A transmitter  8500   a  displays information indicating that the transmitter  8500   a  is capable of visible light communication, by superimposing the information on a projected image. The information is displayed, for example, only for a predetermined time after the transmitter  8500   a  is activated. 
     The transmitter  8500   a  transmits the information indicating that the transmitter  8500   a  is capable of visible light communication, to a connected device  8500   c . The device  8500   c  displays that the transmitter  8500   a  is capable of visible light communication. As an example, the device  8500   c  displays that the transmitter  8500   a  is capable of visible light communication, on a display of the device  8500   c . In the case where the connected transmitter  8500   a  is capable of visible light communication, the device  8500   c  transmits visible light communication data to the transmitter  8500   a . The information that the transmitter  8500   a  is capable of visible light communication may be displayed when the device  8500   c  is connected to the transmitter  8500   a  or when the visible light communication data is transmitted from the device  8500   c  to the transmitter  8500   a . In the case of displaying the information when the visible light communication data is transmitted from the device  8500   c , the transmitter  8500   a  may obtain identification information indicating visible light communication from the data and, if the identification information indicates that the visible light communication data is included in the data, display that the transmitter  8500   a  is capable of visible light communication. 
     By displaying that the transmitter (lighting, projector, video display device, etc.) is capable of visible light communication or whether or not the transmitter is capable of visible light communication on the projection screen or the display of the device in this way, the user can easily recognize whether or not the transmitter is capable of visible light communication. This prevents a failure of visible light communication even though visible light communication data is transmitted from the device to the transmitter. 
     (Information Obtainment Using Visible Light Communication Signal) 
       FIG. 479  is a diagram illustrating an example of application of visible light communication. 
     A transmitter  8501   a  receives video data and signal data from a device  8501   c , and displays a visible light communication image  8501   b . A receiver  8501   d  captures the visible light communication image  8501   b , to receive a signal included in the visible light communication image. The receiver  8501   d  communicates with the device  8501   c  based on information (address, password, etc.) included in the received signal, and receives the video displayed by the transmitter  8501   a  and its ancillary information (video ID, URL, password, SSID, translation data, audio data, hash tag, product information, purchase information, coupon, availability information, etc.). The device  8501   c  may transmit, to a server  8501   e , the status of transmission to the transmitter  8501   a  so that the receiver  8501   d  may obtain the information from the server  8501   e.    
     (Data Format) 
       FIG. 480  is a diagram illustrating a format of visible light communication data. 
     Data illustrated in (a) in  FIG. 480  has a video address table indicating the position of video data in a storage area, and a position address table indicating the position of signal data transmitted by visible light communication. A video display device not capable of visible light communication refers only to the video address table, and therefore video display is not affected even when the signal address table and signal data are included in the input. Backward compatibility with the video display device not capable of visible light communication is maintained in this manner. 
     In a data format illustrated in (b) in  FIG. 480 , an identifier indicating that data which follows is video data is positioned before video data, and an identifier indicating that data which follows is signal data is positioned before signal data. Since the identifier is inserted in the data only when there is video data or signal data, the total amount of code can be reduced. Alternatively, identification information indicating whether data is video data or signal data may be provided. Moreover, program information may include identification information indicating whether or not the program information includes visible light communication data. The inclusion of the identification information indicating whether or not the program information includes visible light communication data allows the user to determine, upon program search, whether or not visible light communication is possible. The program information may include an identifier indicating that the program information includes visible light communication data. Furthermore, adding an identifier or identification information on a data basis makes it possible to switch the luminance or switch the process such as superresolution on a data basis, which contributes to a lower error rate in visible light communication. 
     The data format illustrated in (a) in  FIG. 480  is suitable for a situation of reading data from a storage medium such a an optical disc, and the data format illustrated in (b) in  FIG. 480  is suitable for streaming data such as television broadcasting. Note that the signal data includes information such as the signal value transmitted by visible light communication, the transmission start time, the transmission end time, the area used for transmission on a display or a projection surface, the luminance of the visible light communication image, the direction of barcode of the visible light communication image, and so on. 
     (Estimation of Stereoscopic Shape and Reception) 
       FIGS. 481 and 482  are diagrams illustrating an example of application of visible light communication. 
     As illustrated in  FIG. 481 , a transmitter  8503   a  such as a projector projects not only video and a visible light communication image but also a distance measurement image. A dot pattern indicated by the distance measurement image is a dot pattern in which the position relation between a predetermined number of dots near an arbitrary dot is different from the position relation between other arbitrary combination of dots. A receiver captures the distance measurement image to specify a local dot pattern, with it being possible to estimate the stereoscopic shape of a projection surface  8503   b . The receiver restores the visible light communication image distorted due to the stereoscopic shape of the projection surface to a 2D image, thereby receiving a signal. The distance measurement image and the visible light communication image may be projected by infrared which is not perceivable by humans. 
     As illustrated in  FIG. 482 , a transmitter  8504   a  such as a projector includes an infrared projection device  8504   b  for projecting a distance measurement image by infrared. A receiver estimates the stereoscopic shape of a projection surface  8504   c , and restores a distorted visible light communication image to receive a signal. The transmitter  8504   a  may project video by visible light, and a visible light communication image by infrared. The infrared projection device  8403   b  may project a visible light communication image by infrared. 
     (Stereoscopic Projection) 
       FIGS. 483 and 484  are diagrams illustrating a visible light communication image display method. 
     In the case of performing stereoscopic projection or in the case of displaying a visible light communication image on a cylindrical display surface, displaying visible light communication images  8505   a  to  8505   f  as illustrated in  FIG. 483  enables reception from a wide angle. Displaying the visible light communication images  8505   a  and  8505   b  enables reception from a horizontally wide angle. By combining the visible light communication images  8505   a  and  8505   b , reception is possible even when a receiver is tilted. The visible light communication images  8505   a  and  8505   b  may be displayed alternately, or the visible light communication image  8505   f  obtained by synthesizing these images may be displayed. Moreover, adding the visible light communication images  8505   c  and  8505   d  enables reception from a vertically wide angle. The visible light communication image boundary may be expressed by providing a part projected in an intermediate color or an unprojected part, as in the visible light communication image  8505   e . Rotating the visible light communication images  8505   a  to  8505   f  enables reception from a wider angle. Though the visible light communication image is displayed on the cylindrical display surface in  FIG. 483 , the visible light communication image may be displayed on a columnar display surface. 
     In the case of performing stereoscopic projection or in the case of displaying a visible light communication image on a spherical display surface, displaying visible light communication images  8506   a  to  8506   d  as illustrated in  FIG. 484  enables reception from a wide angle. In the visible light communication image  8506   a , the receivable area in the horizontal direction is wide, but the receivable area in the vertical direction is narrow. Hence, the visible light communication image  8506   a  is combined with the visible light communication image  8506   b  having the opposite property. The visible light communication images  8506   a  and  8506   b  may be displayed alternately, or the visible light communication image  8506   c  obtained by synthesizing these images may be displayed. The part where barcodes concentrate as in the upper part of the visible light communication image  8506   a  is fine in display, and there is a high possibility of a signal reception error. Such a reception error can be prevented by displaying this part in an intermediate color as in the visible light communication image  8506   d  or by not projecting any image in this part. 
     (Communication Protocol Different According to Zone) 
       FIG. 485  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
     A receiver  8420   a  receives zone information form a base station  8420   h , recognizes in which position the receiver  8420   a  is located, and selects a reception protocol. The base station  8420   h  is, for example, a mobile phone communication base station, a W-Fi access point, an IMES transmitter, a speaker, or a wireless transmitter (Bluetooth®, ZigBee, specified low power radio station, etc.). The receiver  8420   a  may specify the zone based on position information obtained from GPS or the like. As an example, it is assumed that communication is performed at a signal frequency of 9.6 kHz in zone A, and communication is performed at a signal frequency of 15 kHz by a ceiling light and at a signal frequency of 4.8 kHz by a signage in zone B. At a position  8420   j , the receiver  8420   a  recognizes that the current position is zone A from information from the base station  8420   h , and performs reception at the signal frequency of 9.6 kHz, thus receiving signals transmitted from transmitters  8420   b  and  8420   c . At a position  84201 , the receiver  8420   a  recognizes that the current position is zone B from information from a base station  84201 , and also estimates that a signal from a ceiling light is to be received from the movement of directing the in camera upward. The receiver  8420   a  performs reception at the signal frequency of 15 kHz, thus receiving signals transmitted from transmitters  8420   e  and  8420   f . At a position  8420   m , the receiver  8420   a  recognizes that the current position is zone B from information from the base station  8420   i , and also estimates that a signal transmitted from a signage is to be received from the movement of sticking out the out camera. The receiver  8420   a  performs reception at the signal frequency of 4.8 kHz, thus receiving a signal transmitted from a transmitter  8420   g . At a position  8420   k , the receiver  8420   a  receives signals from both of the base stations  8420   h  and  8420   i  and cannot determine whether the current position is zone A or zone B. The receiver  8420   a  accordingly performs reception at both 9.6 kHz and 15 kHz. The part of the protocol different according to zone is not limited to the frequency, and may be the transmission signal modulation scheme, the signal format, or the server inquired using an ID. The base station  8420   h  or  8420   i  may transmit the protocol in the zone to the receiver, or transmit only the ID indicating the zone to the receiver so that the receiver obtains protocol information from a server using the zone ID as a key. 
     Transmitters  8420   b  to  8420   f  each receive the zone ID or protocol information from the base station  8420   h  or  8420   i , and determine the signal transmission protocol. The transmitter  8420   d  that can receive the signals from both the base stations  8420   h  and  8420   i  uses the protocol of the zone of the base station with a higher signal strength, or alternately use both protocols. 
     (Recognition of Zone and Service for Each Zone) 
       FIG. 486  is a diagram illustrating an example of operation of a transmitter and a receiver in Embodiment 17. 
     A receiver  8421   a  recognizes a zone to which the position of the receiver  8421   a  belongs, from a received signal. The receiver  8421   a  provides a service (coupon distribution, point assignment, route guidance, etc.) determined for each zone. As an example, the receiver  8421   a  receives a signal transmitted from the left of a transmitter  8421   b , and recognizes that the receiver  8421   a  is located in zone A. Here, the transmitter  8421   b  may transmit a different signal depending on the transmission direction. Moreover, the transmitter  8421   b  may, through the use of a signal of the light emission pattern such as  2217   a , transmit a signal so that a different signal is received depending on the distance to the receiver. The receiver  8421   a  may recognize the position relation with the transmitter  8421   b  from the direction and size in which the transmitter  8421   b  is captured, and recognize the zone in which the receiver  8421   a  is located. 
     Signals indicating the same zone may have a common part. For example, the first half of an ID indicating zone A, which is transmitted from each of the transmitters  8421   b  and  8421   c , is common. This enables the receiver  8421   a  to recognize the zone where the receiver  8421   a  is located, merely by receiving the first half of the signal. 
     Conclusion of this Embodiment 
     An information communication method in this embodiment is an information communication method of transmitting a signal using a change in luminance, the information communication method including: determining a plurality of patterns of the change in luminance, by modulating each of a plurality of signals to be transmitted; and transmitting, by each of a plurality of light emitters changing in luminance according to any one of the plurality of determined patterns of the change in luminance, a signal corresponding to the pattern, wherein in the transmitting, each of two or more light emitters of the plurality of light emitters changes in luminance at a different frequency so that light of one of two types of light different in luminance is output per a time unit determined for the light emitter beforehand and that the time unit determined for each of the two or more light emitters is different. 
     In this way, two or more light emitters (e.g. transmitters as lighting devices) each change in luminance at a different frequency, as in the operation described with reference to  FIG. 441 . Therefore, a receiver that receives signals (e.g. light emitter IDs) from these light emitters can easily obtain the signals separately from each other. 
     For example, in the transmitting, each of the plurality of light emitters may change in luminance at any one of at least four types of frequencies, and the two or more light emitters of the plurality of transmitters may change in luminance at the same frequency. For example, in the transmitting, the plurality of light emitters each change in luminance so that a luminance change frequency is different between all light emitters which, in the case where the plurality of light emitters are projected on a light receiving surface of an image sensor for receiving the plurality of signals, are adjacent to each other on the light receiving surface. 
     In this way, as long as there are at least four types of frequencies used for luminance changes, even in the case where two or more light emitters change in luminance at the same frequency, i.e. in the case where the number of types of frequencies is smaller than the number of light emitters, it can be ensured that the luminance change frequency is different between all light emitters adjacent to each other on the light receiving surface of the image sensor based on the four color problem or the four color theorem, as in the operation described with reference to  FIG. 442 . As a result, the receiver can easily obtain the signals transmitted from the plurality of light emitters, separately from each other. 
     For example, in the transmitting, each of the plurality of light emitters may transmit the signal, by changing in luminance at a frequency specified by a hash value of the signal. 
     In this way, each of the plurality of light emitters changes in luminance at the frequency specified by the hash value of the signal (e.g. light emitter ID), as in the operation described with reference to  FIG. 441 . Accordingly, upon receiving the signal, the receiver can determine whether or not the frequency specified from the actual change in luminance and the frequency specified by the hash value match. That is, the receiver can determine whether or not the received signal (e.g. light emitter ID) has an error. 
     For example, the information communication method may further include: calculating, from a signal to be transmitted which is stored in a signal storage unit, a frequency corresponding to the signal according to a predetermined function, as a first frequency; determining whether or not a second frequency stored in a frequency storage unit and the calculated first frequency match; and in the case of determining that the first frequency and the second frequency do not match, reporting an error, wherein in the case of determining that the first frequency and the second frequency match, in the determining, a pattern of the change in luminance is determined by modulating the signal stored in the signal storage unit, and in the transmitting, the signal stored in the signal storage unit is transmitted by any one of the plurality of light emitters changing in luminance at the first frequency according to the determined pattern. 
     In this way, whether or not the frequency stored in the frequency storage unit and the frequency calculated from the signal stored in the signal storage unit (ID storage unit) match is determined and, in the case of determining that the frequencies do not match, an error is reported, as in the operation described with reference to  FIG. 448 . This eases abnormality detection on the signal transmission function of the light emitter. 
     For example, the information communication method may further include: calculating a first check value from a signal to be transmitted which is stored in a signal storage unit, according to a predetermined function; determining whether or not a second check value stored in a check value storage unit and the calculated first check value match; and in the case of determining that the first check value and the second check value do not match, reporting an error, wherein in the case of determining that the first check value and the second check value match, in the determining, a pattern of the change in luminance is determined by modulating the signal stored in the signal storage unit, and in the transmitting, the signal stored in the signal storage unit is transmitted by any one of the plurality of light emitters changing in luminance at the first frequency according to the determined pattern. 
     In this way, whether or not the check value stored in the check value storage unit and the check value calculated from the signal stored in the signal storage unit (ID storage unit) match is determined and, in the case of determining that the check values do not match, an error is reported, as in the operation described with reference to  FIG. 448 . This eases abnormality detection on the signal transmission function of the light emitter. 
     An information communication method in this embodiment is an information communication method of obtaining information from a subject, the information communication method including: setting an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a plurality of bright lines corresponding to a plurality of exposure lines included in the image sensor appear according to a change in luminance of the subject; obtaining a bright line image including the plurality of bright lines, by capturing the subject that changes in luminance by the image sensor with the set exposure time; obtaining the information by demodulating data specified by a pattern of the plurality of bright lines included in the obtained image; and specifying a luminance change frequency of the subject, based on the pattern of the plurality of bright lines included in the obtained bright line image. For example, in the specifying, a plurality of header patterns that are included in the pattern of the plurality of bright lines and are a plurality of patterns each determined beforehand to indicate a header are specified, and a frequency corresponding to the number of pixels between the plurality of header patterns is specified as the luminance change frequency of the subject. 
     In this way, the luminance change frequency of the subject is specified, as in the operation described with reference to  FIG. 443 . In the case where a plurality of subjects that differ in luminance change frequency are captured, information from these subjects can be easily obtained separately from each other. 
     For example, in the obtaining of a bright line image, the bright line image including a plurality of patterns represented respectively by the plurality of bright lines may be obtained by capturing a plurality of subjects each of which changes in luminance, and in the obtaining of the information, in the case where the plurality of patterns included in the obtained bright line image overlap each other in a part, the information may be obtained from each of the plurality of patterns by demodulating the data specified by a part of each of the plurality of patterns other than the part. 
     In this way, data is not demodulated from the overlapping part of the plurality of patterns (the plurality of bright line patterns), as in the operation described with reference to  FIG. 445 . Obtainment of wrong information can thus be prevented. 
     For example, in the obtaining of a bright line image, a plurality of bright line images may be obtained by capturing the plurality of subjects a plurality of times at different timings from each other, in the specifying, for each bright line image, a frequency corresponding to each of the plurality of patterns included in the bright line image may be specified, and in the obtaining of the information, the plurality of bright line images may be searched for a plurality of patterns for which the same frequency is specified, the plurality of patterns searched for may be combined, and the information may be obtained by demodulating the data specified by the combined plurality of patterns. 
     In this way, the plurality of bright line images are searched for the plurality of patterns (the plurality of bright line patterns) for which the same frequency is specified, the plurality of patterns searched for are combined, and the information is obtained from the combined plurality of patterns. Hence, even in the case where the plurality of subjects are moving, information from the plurality of subjects can be easily obtained separately from each other. 
     For example, the information communication method may further include: transmitting identification information of the subject included in the obtained information and specified frequency information indicating the specified frequency, to a server in which a frequency is registered for each set of identification information; and obtaining related information associated with the identification information and the frequency indicated by the specified frequency information, from the server. 
     In this way, the related information associated with the identification information (ID) obtained based on the luminance change of the subject (transmitter) and the frequency of the luminance change is obtained, as in the operation described with reference to  FIG. 447 . By changing the luminance change frequency of the subject and updating the frequency registered in the server with the changed frequency, a receiver that has obtained the identification information before the change of the frequency is prevented from obtaining the related information from the server. That is, by changing the frequency registered in the server according to the change of the luminance change frequency of the subject, it is possible to prevent a situation where a receiver that has previously obtained the identification information of the subject can obtain the related information from the server for an indefinite period of time. 
     For example, the information communication method may further include: obtaining identification information of the subject, by extracting a part from the obtained information; and specifying a number indicated by the obtained information other than the part, as a luminance change frequency set for the subject. 
     In this way, the identification information of the subject and the luminance change frequency set for the subject can be included independently of each other in the information obtained from the pattern of the plurality of bright lines, as in the operation described with reference to  FIG. 444 . This contributes to a higher degree of freedom of the identification information and the set frequency. 
     Embodiment 18 
     This embodiment describes each example of application using a receiver such as a smartphone and a transmitter for transmitting information as an LED blink pattern in Embodiments 1 to 17 described above. 
       FIG. 487  is a diagram illustrating an example of a transmission signal in Embodiment 18. 
     A transmission signal D is divided into data segments Dx (e.g. Dx=D 1 , D 2 , D 3 ) of a predetermined size, and a header Hdr and an error detection/correction frame check sequence FCS calculated from each data segment are added to the data segment. A header Hdr 2  and an error detection/correction frame check sequence FCS 2  calculated from the original data are added, too. Data made up of Hdr, Dx, and FCS is a structure for reception by an image sensor. Since the image sensor is suitable for reception of continuous data in a short time, Hdr, Dx, and FCS are transmitted continuously. Data made up of Hdr 2 , Dx, and FCS 2  is a structure for reception by an illuminance sensor. While Hdr and FCS received by the image sensor are desirably short, Hdr 2  and FCS 2  received by the illuminance sensor may each be a longer signal sequence. The use of a longer signal sequence for Hdr 2  enhances the header detection accuracy. When FCS 2  is longer, a code capable of detecting and correcting many bit errors can be employed, which leads to improved error detection/correction performance. Note that, instead of transmitting Hdr 2  and FCS 2 , Hdr and FCS may be received by the illuminance sensor. The illuminance sensor may receive both Hdr and Hdr 2  or both FCS and FCS 2 . 
       FIG. 488  is a diagram illustrating an example of a transmission signal in Embodiment 18. 
     FCS 2  is a long signal. Frequently inserting such FCS 2  causes a decrease in reception efficiency of the image sensor. In view of this, the insertion frequency of FCS 2  is reduced, and a signal PoFCS 2  indicating the location of FCS 2  is inserted instead. For example, in the case of using 4-value PPM having 2-bit information per unit time for signal representation, 16 transmission time units are necessary when CRC32 is used for FCS 2 , whereas PoFCS 2  with a range of 0 to 3 can be transmitted in one time unit. Since the transmission time is shortened as compared with the case of inserting only FCS 2 , the reception efficiency of the image sensor can be improved. The illuminance sensor receives PoFCS 2  following the transmission signal D, specifies the transmission time of FCS 2  from PoFCS 2 , and receives FCS 2 . The illuminance sensor further receives PoFCS 2  following FCS 2 , specifies the transmission time of the next FCS 2 , and receives the next FCS 2 . If FCS 2  received first and FCS 2  received next are the same, the receiver estimates that the same signal is being received. 
       FIGS. 489A to 489C  are each a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
     In the captured image illustrated in  FIG. 489A , a transmitter is shown small and so the number of bright lines is small. Only a small amount of data can be received at one time from this captured image. The captured image illustrated in  FIG. 489B  is an image captured using zoom, where the transmitter is shown large and so the number of bright lines is large. Thus, a large amount of data can be received at one time by using zoom. In addition, data can be received from far away, and a signal of a small transmitter can be received. Optical zoom or Ex zoom is employed as the zoom method. Optical zoom is realized by increasing the focal length of a lens. Ex zoom is a zoom method in which, in the case of performing imaging with a lower resolution than the imaging element capacity, not all but only a part of the imaging elements is used to thereby enlarge a part of the captured image. The captured image illustrated in  FIG. 489C  is an image captured using electronic zoom (image enlargement). Though the transmitter is shown large, bright lines are thicker in the enlargement by electronic zoom, and the number of bright lines is unchanged from pre-zoom. Hence, the reception characteristics are unchanged from pre-zoom. 
       FIGS. 490A and 490B  are each a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
     The captured image illustrated in  FIG. 490A  is an image captured with focus on a subject. The captured image illustrated in  FIG. 490B  is an image captured out of focus. In the captured image illustrated in  FIG. 490B , bright lines can be observed even in the surroundings of the actual transmitter because the image is captured out of focus, so that more bright lines can be observed. Thus, more data can be received at one time and also data can be received farther away, by out-of-focus imaging. Imaging in macro mode can produce the same image as the captured image illustrated in  FIG. 490B . 
       FIGS. 491A to 491C  are each a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. 
     The image illustrated in  FIG. 491A  is obtained by setting the exposure time to be longer than that in the visible light communication mode and shorter than that in the normal imaging mode. The imaging mode for obtaining such an image is referred to as “bright line detection mode” (intermediate mode). In the image illustrated in  FIG. 491A , bright lines of a transmitter are observed at the center left, while a darker normal captured image appears in the other part. When this image is displayed on the receiver, the user can easily point the receiver at the intended transmitter and capture the transmitter. In the bright line detection mode, an image is captured darker than in the normal imaging mode. Accordingly, imaging is performed in a high sensitivity mode to capture an image having brightness easily visible by humans, i.e. an image similar to that in the normal imaging mode. Since excessively high sensitivity causes the darker parts of the bright lines to become brighter, the sensitivity is set to such a level that allows the bright lines to be observed. The receiver switches to the visible light communication mode, and receives the transmission signal of the transmitter captured in the part designated by, for example, the user touching the image. The receiver may automatically switch to the visible light communication mode and receive the signal in the case where any bright line (transmission signal) is found in the captured image. 
     The receiver detects the transmission signal from the bright lines in the captured image, and highlights the detected part as illustrated in  FIG. 491B . The receiver can thus present the signal transmission part clearly to the user. The bright lines may be observed with regard to not only the transmission signal but also the pattern of the subject. Therefore, instead of determining whether or not there is the transmission signal from the bright lines in one image, it may be determined that there is the transmission signal in the case where the positions of the bright lines change in a plurality of images. 
     The image captured in the bright line detection mode is darker than the image captured in the normal imaging mode, and is not easily visible. Hence, the image with visibility increased by image processing may be displayed. The image illustrated in  FIG. 491C  is an example of an image in which the edges are extracted and the boundary of the imaging object is enhanced. 
       FIG. 492  is a diagram illustrating an example of an image (bright line image) captured by a receiver in Embodiment 18. In detail,  FIG. 492  illustrates an image obtained by capturing a transmitter whose signal transmission period is 1/9600 second, with the ratio of exposure time indicated in the lower part of the drawing. When the exposure time is shorter than the transmission period of 1/9600 second, the captured image is roughly the same, and clear bright lines can be captured. When the exposure time is longer, the bright line contours are blurred. In this signal representation example, however, the bright line pattern is observable and the signal can be received as long as the exposure time is up to about 1.5 times the transmission period. Moreover, in this signal representation example, the bright lines are observable as long as the exposure time is up to about 20 times the transmission period. The exposure time of this range is available as the exposure time in the bright line detection mode. 
     The upper limit of the exposure time that enables signal reception differs depending on the method of signal representation. The use of such a signal representation rule in which the number of bright lines is smaller and the interval between the bright lines is longer enables signal reception with a longer exposure time and also enables observation of bright lines with a longer exposure time, though the transmission efficiency is lower. 
     (Exposure Time in Intermediate Imaging Mode) 
     As illustrated in  FIG. 492 , clear bright lines are observable when the exposure time is up to about 3 times the modulation period. Since the modulation frequency is greater than or equal to 480 Hz, the exposure time in the intermediate imaging mode (intermediate mode) is desirably less than or equal to 1/160 second. 
     If the exposure time is less than or equal to 1/10000 second, an object not emitting light is hard to be seen under illumination light even when captured in the high sensitivity mode. Accordingly, the exposure time in the intermediate imaging mode is desirably greater than or equal to 1/10000 second. This limitation is, however, expected to be eased by future improvement in sensitivity of imaging elements. 
       FIG. 493  is a diagram illustrating an example of a transmission signal in Embodiment 18. 
     A receiver receives a series of signals by combining a plurality of received data segments. Therefore, if a transmission signal is abruptly changed, data segments before and after the change are mixed with each other, making it impossible to accurately combine the signals. In view of this, upon changing the transmission signal, a transmitter performs normal illumination for a predetermined time as a buffer zone while transmitting no signal, as in (a) in  FIG. 493 . In the case where no signal can be received for a predetermined time T 2  shorter than the above-mentioned predetermined time T 1 , the receiver abandons previously received data segments, thus avoiding mixture of data segments before and after the change. As an alternative, upon changing the transmission signal, the transmitter repeatedly transmits a signal X for notifying the change of the transmission signal, as in (b) in  FIG. 493 . Such repeated transmission prevents a failure to receive the transmission signal change notification X. As another alternative, upon changing the transmission signal, the transmitter repeatedly transmits a preamble, as in (c) in  FIG. 493 . In the case of receiving the preamble in a shorter period than the period in which the preamble appears in the normal signal, the receiver abandons previously received data segments. 
       FIG. 494  is a diagram illustrating an example of operation of a receiver in Embodiment 18. 
     An image illustrated in (a) in  FIG. 494  is an image obtained by capturing a transmitter in just focus. By out-of-focus imaging, a receiver can capture an image illustrated in (b) in  FIG. 494 . Further out of focus leads to a captured image illustrated in (c) in  FIG. 494 . In (c) in  FIG. 494 , bright lines of a plurality of transmitters overlap each other, and the receiver cannot perform signal reception. Hence, the receiver adjusts the focus so that the bright lines of the plurality of transmitters do not overlap each other. In the case where only one transmitter is present in the imaging range, the receiver adjusts the focus so that the size of the transmitter is maximum in the captured image. 
     The receiver may compress the captured image in the direction parallel to the bright lines, but do not perform image compression in the direction perpendicular to the bright lines. Alternatively, the receiver reduces the degree of compression in the perpendicular direction. This prevents a reception error caused by the bright lines being blurred by compression. 
       FIGS. 495 and 496  are each a diagram illustrating an example of an instruction to a user displayed on a screen of a receiver in Embodiment 18. 
     By capturing a plurality of transmitters, a receiver can estimate the position of the receiver using triangulation from position information of each transmitter and the position, size, and angle of each transmitter in the captured image. Accordingly, in the case where only one transmitter is captured in a receivable state, the receiver instructs the imaging direction or the moving direction by displaying an image including an arrow or the like, to cause the user to change the direction of the receiver or move backward so as to capture a plurality of transmitters. (a) in  FIG. 495  illustrates a display example of an instruction to turn the receiver to the right to capture a transmitter on the right side. (b) in  FIG. 495  illustrates a display example of an instruction to move backward to capture a transmitter in front.  FIG. 496  illustrates a display example of an instruction to shake the receiver or the like to capture another transmitter, because the position of another transmitter is unknown to the receiver. Though it is desirable to capture a plurality of transmitters in one image, the position relation between transmitters in a plurality of images may be estimated using image processing or the sensor value of the 9-axis sensor. The receiver may inquire of a server about position information of nearby transmitters using an ID received from one transmitter, and instruct the user to capture a transmitter that is easiest to capture. 
     The receiver detects that the user is moving the receiver from the sensor value of the 9-axis sensor and, after a predetermined time from the end of the movement, displays a screen based on the last received signal. This prevents a situation where, when the user points the receiver to the intended transmitter, a signal of another transmitter is received during the movement of the receiver and as a result a process based on the transmission signal of the unintended transmitter is accidentally performed. 
     The receiver may continue the reception process during the movement, and perform a process based on the received signal, e.g. Information obtainment from the server using the received signal as a key. In this case, after the process the receiver still continues the reception process, and performs a process based on the last received signal as a final process. 
     The receiver may process a signal received a predetermined number of times, or notify the signal received the predetermined number of times to the user. The receiver may process a signal received a largest number of times during the movement. 
     The receiver may include notification means for notifying the user when signal reception is successful or when a signal is detected in a captured image. The notification means performs notification by sound, vibration, display update (e.g. popup display), or the like. This enables the user to recognize the presence of a transmitter. 
       FIG. 497  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
     A plurality of transmitters such as displays are arranged adjacent to each other. In the case of transmitting the same signal, the plurality of transmitters synchronize the signal transmission timing, and transmit the signal from the entire surface as in (a) in  FIG. 497 . This allows a receiver to observe the plurality of displays as one large transmitter, so that the receiver can receive the signal faster or from a longer distance. In the case where the plurality of transmitters transmit different signals, the plurality of transmitters transmit the signals while providing a buffer zone (non-transmission area) where no signal is transmitted, as in (b) in  FIG. 497 . This allows the receiver to recognize the plurality of transmitters as separate transmitters with the buffer zone in between, so that the receiver can receive the signals separately. 
       FIG. 498  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
     As illustrated in (a) in  FIG. 498 , a liquid crystal display provides a backlight off period, and changes the liquid crystal state during backlight off to make the image in the state change invisible, thus enhancing dynamic resolution. On the liquid crystal display performing such backlight control, a signal is superimposed according to the backlight on period as illustrated in (b) in  FIG. 498 . Continuously transmitting the set of data (Hdr, Data, FCS) contributes to higher reception efficiency. The light emitting unit is in a bright state (Hi) in the first and last parts of the backlight on period. This is because, if the dark state (Lo) of the light emitting unit is continuous with the backlight off period, the receiver cannot determine whether Lo is transmitted as a signal or the light emitting unit is in a dark state due to the backlight off period. 
     A signal decreased in average luminance may be superimposed in the backlight off period. 
     Signal superimposition causes the average luminance to change as compared with the case where no signal is superimposed. Hence, adjustment such as increasing/decreasing the backlight off period or increasing/decreasing the luminance during backlight on is performed so that the average luminance is equal. 
       FIG. 499  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
     A liquid crystal display can reduce the luminance change of the entire screen, by performing backlight control at a different timing depending on position. This is called backlight scan. Backlight scan is typically performed so that the backlight is turned on sequentially from the end, as in (a) in  FIG. 499 . A captured image  8802   a  is obtained as a result. In the captured image  8802   a , however, the part including the bright lines is divided, and there is a possibility that the entire screen of the display cannot be estimated as one transmitter. The backlight scan order is accordingly set so that all light emitting parts (signal superimposition parts) are connected when the vertical axis is the spatial axis in the backlight scan division direction and the horizontal axis is the time axis, as in (b) in  FIG. 499 . A captured image  8802   b  is obtained as a result. In the captured image  8802   b , all bright line parts are connected, facilitating estimation that this is a transmission signal from one transmitter. Besides, since the number of continuously receivable bright lines increases, faster or longer-distance signal reception is possible. Moreover, the size of the transmitter is easily estimated, and therefore the position of the receiver can be accurately estimated from the position, size, and angle of the transmitter in the captured image. 
       FIG. 500  is a diagram illustrating an example of a signal transmission method in Embodiment 18. 
     In time-division backlight scan, in the case where the backlight on period is short and the light emitting parts (signal superimposition parts) cannot be connected on the graph in which the vertical axis is the spatial axis in the backlight scan division direction and the horizontal axis is the time axis, signal superimposition is performed in each light emitting part according to the backlight illumination timing, in the same way as in  FIG. 498 . Here, by controlling the backlight so that the distance from another backlight on part on the graph is maximum, it is possible to prevent mixture of bright lines in adjacent parts. 
       FIG. 501  is a diagram for describing a use case in Embodiment 18. A system in this embodiment includes a lighting fixture  100  that performs visible light communication, a wearable device  101  having a visible light communication function, a smartphone  102 , and a server  103 . 
     This embodiment is intended to save, through the use of visible light communication, the user&#39;s trouble when shopping in a store, thereby reducing the time for shopping. Conventionally, when the user buys a product in a store, the user needs to search for the site of the store and obtain coupon information beforehand. There is also a problem that it takes time to search the store for the product for which the coupon is available. 
     As illustrated in  FIG. 501 , the lighting fixture  100  periodically transmits lighting ID information of the lighting fixture  100  using visible light communication, in front of the store (an electronics retail store is assumed as an example). The wearable device  101  of the user receives the lighting ID information, and transmits the lighting ID information to the smartphone  102  using near field communication. The smartphone  102  transmits information of the user and the lighting ID information to the server  103  using a mobile line or the like. The smartphone  102  receives point information, coupon information, and the like of the store in front of the user, from the server  103 . The user views the information received from the server  103 , on the wearable device  101  or the smartphone  102 . Thus, the user can buy displayed product information of the store on the spot, or be guided to an exhibit in the store. This is described in detail below, with reference to drawings. 
       FIG. 502  is a diagram illustrating an information table transmitted from the smartphone  102  to the server  103 . The smartphone  102  transmits not only the membership number, the store ID information, the transmission time, and the position information of the store held in the smartphone  102 , but also the user preference information, biological information, search history, and behavior history information held in the smartphone  102 . 
       FIG. 503  is a block diagram of the server  103 . A transmission and reception unit  201  receives the information from the smartphone  102 . A control unit  202  performs overall control. A membership information DB  203  holds each membership number and the name, date of birth, point information, purchase history, and the like of the user of the membership number. A store DB  204  holds each store ID and in-store information such as product information sold in the store, display information of the store, and map information of the store. A notification information generation unit  205  generates coupon information or recommended product information according to user preference. 
       FIG. 504  is a flowchart illustrating an overall process of the system. The wearable device  102  receives the lighting ID from the lighting  100  (Step S 301 ). The wearable device  101  then transmits the lighting ID to the smartphone  102 , for example using proximity wireless communication such as Bluetooth® (Step S 302 ). The smartphone  102  transmits the user history information and the membership number held in the smartphone  102  illustrated in  FIG. 502  and the lighting ID, to the server  103  (Step S 303 ). When the server  103  receives the data, the data is first sent to the control unit  202  (Step S 304 ). The control unit  202  refers to the membership DB  203  with the membership number, and obtains membership information (Step S 305 ). The control unit  202  also refers to the store DB  204  with the lighting ID, and obtains store information (Step S 306 ). The store information includes product information in stock in the store, product information which the store wants to promote, coupon information, in-store map information, and the like. The control unit  202  sends the membership information and the store information to the notification information generation unit (Step S 307 ). The notification information generation unit  205  generates advertisement information suitable for the user from the membership information and the store information, and sends the advertisement information to the control unit  202  (Step S 308 ). The control unit  202  sends the membership information and the advertisement information to the transmission and reception unit  201  (Step S 309 ). The membership information includes point information, expiration date information, and the like of the user. The transmission and reception unit  201  transmits the membership information and the advertisement information to the smartphone  102  (Step S 310 ). The smartphone  102  displays the received information on the display screen (Step S 311 ). 
     The smartphone  102  further transfers the information received from the server  103 , to the wearable device  101  (Step S 312 ). If the notification setting of the wearable device  101  is ON, the wearable device  101  displays the information (Step S 314 ). When the wearable device displays the information, it is desirable to alert the user by vibration or the like, for the following reason. Since the user does not always enter the store, even when the coupon information or the like is transmitted, the user might be unaware of it. 
       FIG. 505  is a diagram illustrating an information table transmitted from the server  103  to the smartphone  102 . A store map DB is in-store guide information indicating which product is displayed in which position in the store. Store product information is product information in stock in the store, product price information, and the like. User membership information is point information, membership card expiration date information, and the like of the user. 
       FIG. 506  is a diagram illustrating flow of screen displayed on the wearable device  101  from when the user receives the information from the server  103  in front of the store to when the user actually buys a product. In front of the store, the points provided when the user visits the store and the coupon information are displayed. 
     When the user taps the coupon information, the information according to the user preference transmitted from the server  103  is displayed. For example when the user taps “TV”, recommended TV information is displayed. When the user presses the buy button, a receiving method selection screen is displayed to enable the user to select the delivery to the home or the reception in the store. In this embodiment, in which store the user is present is known, and so there is an advantage that the user can receive the product in the store. When the user selects “guide to sales floor” in flow  403 , the wearable device  101  switches to a guide mode. This is a mode of guiding the user to a specific location using an arrow and the like, and the user can be guided to the location where the selected product is actually on display. After the user is guided to the store shelf, the wearable device  101  switches to a screen inquiring whether or not to buy the product. The user can determine whether or not to buy the product, after checking the size, the color, the usability and the like with the actual product. 
     Visible light communication in the present disclosure allows the position of the user to be specified accurately. Therefore, for example in the case where the user is likely to enter a dangerous area in a factory as in  FIG. 507 , a warning can be issued to the user. Whether or not to issue a warning may be determined by the wearable device. It is thus possible to create such a warning system with a high degree of freedom that warns children of a specific age or below. 
     Embodiment 19 
       FIG. 508  is a diagram illustrating a service provision system using the reception method described in any of the foregoing embodiments. 
     First, a company A ex 8000  managing a server ex 8002  is requested to distribute information to a mobile terminal, by another company B or individual ex 8001 . For example, the distribution of detailed advertisement information, coupon information, map information, or the like to the mobile terminal that performs visible light communication with a signage is requested. The company A ex 8000  managing the server manages information distributed to the mobile terminal in association with arbitrary ID information. A mobile terminal ex 8003  obtains ID information from a subject ex 8004  by visible light communication, and transmits the obtained ID information to the server ex 8002 . The server ex 8002  transmits the information corresponding to the ID information to the mobile terminal, and counts the number of times the information corresponding to the ID information is transmitted. The company A ex 8000  managing the server charges the fee corresponding to the count, to the requesting company B or individual ex 8001 . For example, a larger fee is charged when the count is larger. 
       FIG. 509  is a flowchart illustrating service provision flow. 
     In Step ex 8000 , the company A managing the server receives the request for information distribution from another company B. In Step ex 8001 , the information requested to be distributed is managed in association with the specific ID information in the server managed by the company A. In Step ex 8002 , the mobile terminal receives the specific ID information from the subject by visible light communication, and transmits it to the server managed by the company A. The visible light communication method has already been described in detail in the other embodiments, and so its description is omitted here. The server transmits the information corresponding to the specific ID information received from the mobile terminal, to the mobile terminal. In Step ex 8003 , the number of times the information is distributed is counted in the server. Lastly, in Step ex 8004 , the fee corresponding to the information distribution count is charged to the company B. By such charging according to the count, the appropriate fee corresponding to the advertising effect of the information distribution can be charged to the company B. 
       FIG. 510  is a flowchart illustrating service provision in another example. The description of the same steps as those in  FIG. 509  is omitted here. 
     In Step ex 8008 , whether or not a predetermined time has elapsed from the start of the information distribution is determined. 
     In the case of determining that the predetermined time has not elapsed, no fee is charged to the company B in Step ex 8011 . In the case of determining that the predetermined time has elapsed, the number of times the information is distributed is counted in Step ex 8009 . In Step ex 8010 , the fee corresponding to the information distribution count is charged to the company B. Since the information distribution is performed free of charge within the predetermined time, the company B can receive the accounting service after checking the advertising effect and the like. 
       FIG. 511  is a flowchart illustrating service provision in another example. The description of the same steps as those in  FIG. 510  is omitted here. 
     In Step ex 8014 , the number of times the information is distributed is counted. In the case of determining that the predetermined time has not elapsed from the start of the information distribution in Step ex 8015 , no fee is charged in Step ex 8016 . In the case of determining that the predetermined time has elapsed, on the other hand, whether or not the number of times the information is distributed is greater than or equal to a predetermined number is determined in Step ex 8017 . In the case where the number of times the information is distributed is less than the predetermined number, the count is reset, and the number of times the information is distributed is counted again. In this case, no fee is charged to the company B regarding the predetermined time during which the number of times the information is distributed is less than the predetermined number. In the case where the count is greater than or equal to the predetermined number in Step ex 8017 , the count is reset and started again in Step ex 8018 . In Step ex 8019 , the fee corresponding to the count is charged to the company B. Thus, in the case where the count during the free distribution time is small, the free distribution time is provided again. This enables the company B to receive the accounting service at an appropriate time. Moreover, in the case where the count is small, the company A can analyze the information and, for example when the information is out of season, suggest the change of the information to the company B. In the case where the free distribution time is provided again, the time may be shorter than the predetermined time provided first. The shorter time than the predetermined time provided first reduces the burden on the company A. Further, the free distribution time may be provided again after a fixed time period. For instance, if the information is influenced by seasonality, the free distribution time is provided again after the fixed time period until the new season begins. 
     Note that the charge fee may be changed according to the amount of data, regardless of the number of times the information is distributed. Distribution of a predetermined amount of data or more may be charged, while distribution is free of charge within the predetermined amount of data. The charge fee may be increased with the increase of the amount of data. Moreover, when managing the information in association with the specific ID information, a management fee may be charged. By charging the management fee, it is possible to determine the fee upon requesting the information distribution. 
     Embodiment 20 
     (Modulation Scheme that Facilitates Reception) 
       FIGS. 512 and 513  are diagrams illustrating an example of signal coding in Embodiment 20. A transmission signal is made up of a header (H) and a body (Body). The header includes a unique signal pattern. A receiver finds this unique pattern from a received signal, recognizes which parts of the received signal represent the header and the body based on the position of the unique pattern, and receives data. 
     In the case where the transmission signal is modulated in a pattern (a), the receiver can receive data when successively receiving the header and the body that follows the header. The duration in which the receiver can continuously receive the signal depends on the size of a transmitter in a captured image. In the case where the transmitter is small or the transmitter is captured from a distance, the duration in which the receiver can continuously receive the signal is short. In the case where the duration in which the receiver can continuously receive the signal is the same as the time taken for transmitting the header and the body, data reception is possible only when the transmission start time and the reception start time of the header are the same. (a) corresponds to the case where the reception duration is a little longer than the transmission time for the header and the body. Each arrow indicates the reception duration. The receiver can receive data when receiving the signal at the timings indicated by the thick arrows, but cannot receive data when receiving the signal at the timings indicated by the thin arrows because the header and the body are not completely contained in the received signal. 
     In the case where the transmission signal is modulated in a pattern (b), data reception is possible at more reception timings. The transmitter transmits the signal modulated with “body, header, body” as one set. The bodies in the same set represent the same signal. The receiver does not need to continuously receive the body, and can restore the body by concatenating the bodies before and after the header. Hence, data reception is possible so long as the receiver can continuously receive the header. In  FIG. 512 , the reception timings at which data can be received are indicated by the thick lines. As illustrated in  FIG. 512 , data reception is possible at more reception timings in the case of (b) than in the case of (a). 
     In the modulation scheme (b), the receiver can restore the body in the case where the body signal length is fixed. The receiver can also restore the body in the case where information of the body signal length is included in the header. Even in the case where the body signal length is variable, if the modulation scheme is defined so that the body modulated by the same transmitter has the same signal length, the receiver can restore the body by estimating the body signal length from the signal length between two headers. In this case, in the modulation scheme (b), a signal corresponding to two headers and two bodies needs to be received at one time. In a modulation scheme (c), on the other hand, merely receiving a signal corresponding to two headers and one body enables the body signal length to be estimated. (c) is the modulation scheme in which “body, header, body, header 2” constitute one set, where data reception is possible so long as the receiver can continuously receive the header. 
     (Communication Using Bright Lines and Image Recognition) 
       FIG. 514  is a diagram illustrating an example of a captured image in Embodiment 20. 
     A receiver can not only read a signal from bright lines in the captured image, but also analyze a part other than the bright lines by image processing. For instance, the receiver receives a signal from a transmitter such as a digital signage. Even in the case where the receiver receives the same signal, the receiver can display a different advertisement depending on an image displayed on a screen of the transmitter. 
     Since the bright lines are noise in image processing, image processing may be performed after interpolating pixel values in the bright line part from pixels right and left of the bright lines. Alternatively, image processing may be performed on an image except the bright line part. 
     (Imaging Element Use Method Suitable for Visible Light Signal Reception) 
       FIG. 515  is a diagram illustrating an example of a receiver in Embodiment 20. 
     The receiver includes an imaging element  8910   a . The imaging element includes effective pixels which constitute a part for capturing an image, optical black for measuring noise such as dark current, and an invalid area  8910   b . The optical black includes VOB for measuring vertical noise and HOB for measuring horizontal noise. Since bright lines appear in a direction  8910   c , during exposure of the VOB or the invalid area  8910   b , bright lines are not obtained and signal reception is impossible. The time during which signal reception is possible can be increased by switching, upon visible light communication, to such an imaging mode that does not use the VOB and the invalid area  8910   b  or minimally uses the VOB and the invalid area  8910   b.    
     The time during which signal reception is possible can be further increased by switching, upon visible light communication, to such an imaging mode that does not reduce the number of vertical pixels by a process such as demosaicing or clipping. 
     When an image is captured in such a mode that does not use the VOB and the invalid area  8910   b  and does not reduce the number of vertical pixels, the timing of exposing the bottom edge of the captured image and the timing of exposing the top edge of the captured image at the next frame are continuous, so that continuous signal reception is possible. Even in the case where the VOB and the like cannot be completely disabled, by modulating the transmission signal by an error correctable scheme, continuous signal reception is possible. 
     In  FIG. 515 , photodiodes in the horizontal direction are exposed simultaneously, as a result of which horizontal bright lines appear. In visible light communication, this exposure mode and an exposure mode of exposing photodiodes in the vertical direction simultaneously are alternately applied to obtain horizontal bright lines and vertical bright lines. Thus, the signal can be stably received regardless of the shape of the transmitter. 
     (Captured Image Size Suitable for Visible Light Signal Reception) 
       FIGS. 516 and 517  are diagrams illustrating an example of a reception method in Embodiment 20. 
     In the case where an effective pixel area of an imaging element is 4:3, top and bottom parts are clipped if an image is captured at 16:9. When horizontal bright lines appear, bright lines are lost due to this clipping, and the time during which signal reception is possible is shortened. Likewise, in the case where the effective pixel area of the imaging element is 16:9, right and left parts are clipped if an image is captured at 4:3. When vertical bright lines appear, the time during which signal reception is possible is shortened. In view of this, an aspect ratio that involves no clipping, i.e. 4:3 in  FIG. 516  and 16:9 in  FIG. 517 , is set as an aspect ratio for imaging in the visible light communication mode. This contributes to a longer time during which reception is possible. 
     (Visible Light Signal Reception Using Zoom) 
       FIG. 518  is a diagram illustrating an example of a reception method in Embodiment 20. 
     A receiver finds an area where bright lines are present in a captured image  8913   a , and performs zoom so that as many bright lines as possible appear. The number of bright lines can be maximized by enlarging the bright line area in the direction perpendicular to the bright line direction until the bright line area lies over the top and bottom edges of the screen as in a captured image  8913   b.    
     The receiver may find an area where bright lines are displayed clearly, and perform zoom so that the area is shown in a large size as in a captured image  8913   c.    
     In the case where a plurality of bright line areas are present in a captured image, the above-mentioned process may be performed for each of the bright line areas, or performed for a bright line area designated by a user from the captured image. 
     (Image Data Size Reduction Method Suitable for Visible Light Signal Reception) 
       FIG. 519  is a diagram illustrating an example of a reception method in Embodiment 20. 
     In the case where the image data size needs to be reduced when sending a captured image (a) from an imaging unit to an image processing unit or from an imaging terminal to a server, reduction or pixel omission in the direction parallel to bright lines as in (c) enables the data size to be reduced without decreasing the amount of information of bright lines. When reduction or pixel omission is performed as in (b) or (d), on the other hand, the number of bright lines decreases or it becomes difficult to recognize bright lines. Upon image compression, too, a decrease in reception efficiency can be prevented by not performing compression in the direction perpendicular to bright lines or by setting the compression rate in the perpendicular direction lower than that in the parallel direction. Note that a moving average filter is applicable to any of the parallel and perpendicular directions, and is effective in both data size reduction and noise reduction. 
     (Modulation Scheme with High Reception Error Detection Accuracy) 
       FIG. 520  is a diagram illustrating an example of a signal modulation method in Embodiment 20. 
     Error detection by a parity bit detects a 1-bit reception error, and so cannot detect a mix-up between “01” and “10” and a mix-up between “00” and “11”. In a modulation scheme (a), “01” and “10” tend to be mixed up because the L position differs only by one between “01” and “10”. In a modulation scheme (b), on the other hand, the L position differs by two between “01” and “10” and between “00” and “11”. Hence, a reception error can be detected with high accuracy through the use of the modulation scheme (b). The same applies to the modulation schemes in  FIGS. 404 to 406 . 
     (Change of Operation of Receiver According to Situation) 
       FIG. 521  is a diagram illustrating an example of operation of a receiver in Embodiment 20. 
     A receiver  8920   a  operates differently according to a situation in which reception starts. For instance, in the case of being activated in Japan, the receiver  8920   a  receives a signal modulated at 60 kHz, and downloads data from a server  8920   d  using the received ID as a key. In the case of being activated in the US, the receiver  8920   a  receives a signal modulated at 50 kHz, and downloads data from a server  8920   e  using the received ID as a key. The situation according to which the operation of the receiver changes includes a location (country or building) where the receiver  8920   a  is present, a base station or a wireless access point (Wi-Fi, Bluetooth, IMES, etc.) in communication with the receiver  8920   a , a time of day, and so on. 
     (Notification of Visible Light Communication to Humans) 
       FIG. 522  is a diagram illustrating an example of operation of a transmitter in Embodiment 20. 
     A light emitting unit in a transmitter  8921   a  repeatedly performs blinking visually recognizable by humans and visible light communication. Blinking visually recognizable by humans can notify humans that visible light communication is possible. Upon seeing that the transmitter  8921   a  is blinking, a user notices that visible light communication is possible. The user accordingly points a receiver  8921   b  at the transmitter  8921   a  to perform visible light communication, and conducts user registration of the transmitter  8921   b.    
     The transmitter may include a visible light communication unit and a blinking unit separately, as illustrated in (b). 
     The transmitter may operate as illustrated in (c) using the modulation scheme in  FIG. 405 or 406 , thereby making the light emitting unit appear blinking to humans while performing visible light communication. As an example, by operating as illustrated in (c) when an abnormal condition or the like occurs in the transmitter and the transmitter is transmitting a signal different from normal, the transmitter can alert the user without stopping visible light communication. 
     (Expansion in Reception Range by Diffusion Plate) 
       FIG. 523  is a diagram illustrating an example of a receiver in Embodiment 20. 
     A receiver  8922   a  is in a normal mode in (a), and in a visible light communication mode in (b). The receiver  8922   a  includes a diffusion plate  8922   b  in front of an imaging unit. In the visible light communication mode, the receiver  8922   a  moves the diffusion plate  8922   b  to be in front of the imaging unit so that a light source is captured wider. Here, the position of the diffusion plate  8922   b  is adjusted to prevent light from a plurality of light sources from overlapping each other. A macro lens or a zoom lens may be used instead of the diffusion plate  8922   b . This enables signal reception from a distant transmitter or a small transmitter. 
     The imaging direction of the imaging unit may be moved instead of moving the diffusion plate  8922   b . An area of an image sensor where the diffusion plate  8922   b  is shown may be used only in the visible light communication mode and not in the normal imaging mode. In this way, the above-mentioned advantageous effect can be achieved without moving the diffusion plate  8922   b  or the imaging unit. 
     (Method of Synchronizing Signal Transmission from a Plurality of Transmitters) 
       FIGS. 524 and 525  are diagrams illustrating an example of a transmission system in Embodiment 20. 
     In the case of using a plurality of projectors for projection mapping or the like, for projection onto one part, there is a need to transmit a signal only from one projector or synchronize the signal transmission timings of the plurality of projectors, in order to avoid interference.  FIG. 524  illustrates a mechanism for synchronization of transmission. 
     Projectors A and B that project onto the same projection surface transmit signals as illustrated in the drawing. A receiver captures the projection surface for signal reception, calculates the time difference between signals a and b, and adjusts the signal transmission timing of each projector. 
     Since the projectors A and B are not synchronous at the operation start, a time (total pause time) during which both the projectors A and B transmit no signal is provided to prevent the signals a and b from overlapping and being unable to be received. The signal transmitted from each projector may be changed as the timing adjustment for the projector progresses. For example, efficient timing adjustment can be made by taking a longer total pause time at the operation start and shortening the total pause time as the timing adjustment progresses. 
     For accurate timing adjustment, it is desirable that the signals a and b are contained in one captured image. The imaging frame rate of the receiver tends to be 60 fps to 7.5 fps. By setting the signal transmission period to less than or equal to 1/7.5 second, the signals a and b can be contained in an image captured at 7.5 fps. By setting the signal transmission period to less than or equal to 1/60 second, the signals a and b can be reliably contained in an image captured at 30 fps. 
       FIG. 525  illustrates synchronization of a plurality of transmitters as displays. The displays to be synchronized are captured so as to be contained within one image, to perform timing adjustment. 
     (Visible Light Signal Reception by Illuminance Sensor and Image Sensor) 
       FIG. 526  is a diagram illustrating an example of operation of a receiver in Embodiment 20. 
     An image sensor consumes more power than an illuminance sensor. Accordingly, when a signal is detected by an illuminance sensor  8940   c , a receiver  8940   a  activates an image sensor  8940   b  to receive the signal. The receiver  8940   a  receives a signal transmitted from a transmitter  8940   d , by the illuminance sensor  8940   c . After this, the receiver  8940   a  activates the image sensor  8940   b , receives the transmission signal of the transmitter  8940   d  by the image sensor, and also recognizes the position of the transmitter  8940   d . At the time when the image sensor  8940   b  receives a part of the signal, if the part is the same as the signal received by the illuminance sensor  8940   c , the receiver  8940   a  provisionally determines that the same signal is received, and performs a subsequent process such as displaying the current position. The determination is completed once the image sensor  8940   b  has successfully received the whole signal. 
     Upon the provisional determination, information that the determination is not completed may be displayed. For instance, the current position is displayed semi-transparently, or a position error is displayed. 
     The part of the signal may be, for example, 20% of the total signal length or an error detection code portion. 
     In a situation as illustrated in (b), the receiver  8940   a  cannot receive signals by the illuminance sensor  8940   c  due to interference, but can recognize the presence of signals. For example, the receiver  8940   a  can estimate that signals are present, in the case where a peak appears in transmission signal modulation frequency when the sensor value of the illuminance sensor  8940   c  is Fourier transformed. Upon estimating that signals are present from the sensor value of the illuminance sensor  8940   c , the receiver  8940   a  activates the image sensor  8940   b  and receives signals from transmitters  8940   e  and  8940   f.    
     (Reception Start Trigger) 
       FIG. 527  is a diagram illustrating an example of operation of a receiver in Embodiment 20. 
     Power is consumed while an image sensor or an illuminance sensor (hereafter referred to as “light receiving sensor”) is on. Stopping the light receiving sensor when not needed and activating it when needed contributes to improved power consumption efficiency. Here, since the illuminance sensor consumes less power than the image sensor, only the image sensor may be controlled while the illuminance sensor is always on. 
     In (a), a receiver  8941   a  detects movement from a sensor value of a 9-axis sensor, and activates a light receiving sensor to start reception. 
     In (b), the receiver  8941   a  detects an operation of tilting the receiver horizontally from the sensor value of the 9-axis sensor, and activates a light receiving sensor pointed upward to start reception. 
     In (c), the receiver  8941   a  detects an operation of sticking the receiver out from the sensor value of the 9-axis sensor, and activates a light receiving sensor in the stick out direction to start reception. 
     In (d), the receiver  8941   a  detects an operation of directing the receiver upward or shaking the receiver from the sensor value of the 9-axis sensor, and activates a light receiving sensor pointed upward to start reception. 
     (Reception Start Gesture) 
       FIG. 528  is a diagram illustrating an example of gesture operation for starting reception by the present communication scheme. 
     A receiver  8942   a  such as a smartphone detects an operation of setting the receiver upright and sliding the receiver in the horizontal direction or repeatedly sliding the receiver in the horizontal direction, from a sensor value of a 9-axis sensor. The receiver  8942   a  then starts reception, and obtains the position of each transmitter  8942   b  based on the received ID. The receiver  8942   a  obtains the position of the receiver, from the relative position relations between the receiver and the plurality of transmitters  8942   b . The receiver  8942   b  can stably capture the plurality of transmitters by being slid, and estimate the position of the receiver with high accuracy by triangulation. 
     This operation may be performed only when the receiver&#39;s home screen is in the foreground. This can prevent the communication from being launched despite the user&#39;s intension while the user is using another application. 
     (Example of Application to Car Navigation System) 
       FIGS. 529 and 530  are diagrams illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A transmitter  8950   b  such as a car navigation system transmits information for wirelessly connecting to the transmitter  8950   b , such as Bluetooth pairing information, Wi-Fi SSID and password, or an IP address. A receiver  8950   a  such as a smartphone establishes wireless connection with the transmitter  8950   b  based on the received information, and performs subsequent communication via the wireless connection. 
     As an example, a user inputs a destination, store information to be searched for, or the like to the smartphone  8950   a . The smartphone  8950   a  transmits the input information to the car navigation system  8950   b  via the wireless connection, and the car navigation system  8950   b  displays route information. As another example, the smartphone  8950   a  is operated as a controller of the car navigation system  8950   b , to control music or video reproduced in the car navigation system  8950   b . As another example, music or video held in the smartphone  8950   a  is reproduced in the car navigation system  8950   b . As another example, the car navigation system  8950   b  obtains nearby store information or road congestion information, and has the smartphone  8950   a  display the information. As another example, upon receiving a call, the smartphone  8950   a  uses a microphone and a speaker of the wirelessly connected car navigation system  8950   b  for conversation. The smartphone  8950   a  may establish wireless connection and performs the above-mentioned operation upon receiving a call. 
     In the case where the car navigation system  8950   b  is set in an automatic connection mode for wireless connection, the car navigation system  8950   b  is wirelessly connected to a registered terminal automatically. In the case where the car navigation system  8950   b  is not in the automatic connection mode, the car navigation system  8950   b  transmits connection information using visible light communication, and waits for connection. The car navigation system  8950   b  may transmit connection information using visible light communication and wait for connection, even in the automatic connection mode. In the case where the car navigation system is manually connected, the automatic connection mode may be cleared, and a terminal automatically connected to the car navigation system may be disconnected. 
     (Example of Application to Content Protection) 
       FIG. 531  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A transmitter  8951   b  such as a television transmits content protection information held in the transmitter  8951   b  or a device  8951   c  connected to the transmitter  8951   b . A receiver  8951   a  such as a smartphone receives the content protection information, and performs content protection for a predetermined time afterward so that content protected by the content protection information in the transmitter  8951   b  or the device  8951   c  can be reproduced. Thus, content held in another device possessed by the user can be reproduced in the receiver. 
     The transmitter  8951   b  may hold the content protection information in a server, and the receiver  8951   a  may obtain the content protection information from the server using a received ID of the transmitter  8951   b  as a key. 
     The receiver  8951   a  may transmit the obtained content protection information to another device. 
     (Example of Application to Electronic Lock) 
       FIG. 532  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8952   a  receives an ID transmitted from a transmitter  8952   b , and transmits the ID to a server  8952   c . When receiving the ID of the transmitter  8952   b  from the receiver  8952   a , the server  8952   c  unlocks a door  8952   d , opens an automatic door, or calls an elevator for moving to a floor registered in the receiver  8952   a  to a floor on which the receiver  8952   a  is present. The receiver  8952   a  thus functions as a key, allowing the user to unlock the door  8952   d  before reaching the door  8952   d  as an example. 
     To prevent malicious operation, the server  8952   c  may verify that the device in communication is the receiver  8952   a , through the use of security protection such as a secure element of the receiver  8952   a . Moreover, to make sure that the receiver  8952   a  is near the transmitter  8952   b , the server  8952   c  may, upon receiving the ID of the transmitter  8952   b , issue an instruction to transmit a different signal to the transmitter  8952   b  and, in the case where the signal is transmitted from the receiver  8952   a , unlock the door  8952   d.    
     (Example of Application to Store Visit Information Transmission) 
       FIG. 533  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8953   a  transmits an ID transmitted from a transmitter  8953   b , to a server  8953   c . The server  8953   c  notifies a store staff  8953   d  of order information associated with the receiver  8953   a . The store staff  8953   d  prepares a product or the like, based on the order information. Since the order has already been processed when the user enters the store, the user can promptly receive the product or the like. 
     (Example of Application to Location-Dependent Order Control) 
       FIG. 534  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8954   a  displays a screen allowing an order only when a transmission signal of a transmitter  8954   b  is received. In this way, a store can avoid taking an order from a customer who is not nearby. 
     Alternatively, the receiver  8954   a  places an order by transmitting an ID of the transmitter  8954   b  in addition to order information. This enables the store to recognize the position of the orderer, and recognize the position to which a product is to be delivered or estimate the time by which the orderer is likely to arrive at the store. The receiver  8954   a  may add the travel time to the store calculated from the moving speed, to the order information. Regarding suspicious purchase based on the current position (e.g. purchase of a ticket of a train departing from a station other than the current position), the receiver. 
     (Example of Application to Route Guidance) 
       FIG. 535  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8955   a  receives a transmission ID of a transmitter  8955   b  such as a guide sign, obtains data of a map displayed on the guide sign from a server, and displays the map data. Here, the server may transmit an advertisement suitable for the user of the receiver  8955   a , so that the receiver  8955   a  displays the advertisement information, too. The receiver  8955   a  displays the route from the current position to the location designated by the user. 
     (Example of Application to Location Notification) 
       FIG. 536  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8956   a  receives an ID transmitted from a transmitter  8956   b  such as a home or school lighting, and transmits position information obtained using the ID as a key, to a terminal  8956   c . A parent having the terminal  8956   c  can thus be notified that his or her child having the receiver  8956   a  has got back home or arrived at the school. As another example, a supervisor having the terminal  8956   c  can recognize the current position of a worker having the receiver  8956   a.    
     (Example of Application to Use Log Storage and Analysis) 
       FIG. 537  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8957   a  receives an ID transmitted from a transmitter  8957   b  such as a sign, obtains coupon information from a server, and displays the coupon information. The receiver  8957   a  stores the subsequent behavior of the user such as saving the coupon, moving to a store displayed in the coupon, shopping in the store, or leaving without saving the coupon, in the server  8957   c . In this way, the subsequent behavior of the user who has obtained information from the sign  8957   b  can be analyzed to estimate the advertisement value of the sign  8957   b.    
     (Example of Application to Screen Sharing) 
       FIGS. 538 and 539  are diagrams illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A transmitter  8960   b  such as a projector or a display transmits information (an SSID, a password for wireless connection, an IP address, a password for operating the transmitter) for wirelessly connecting to the transmitter  8960   b , or transmits an ID which serves as a key for accessing such information. A receiver  8960   a  such as a smartphone, a tablet, a notebook computer, or a camera receives the signal transmitted from the transmitter  8960   b  to obtain the information, and establishes wireless connection with the transmitter  8960   b . The wireless connection may be made via a router, or directly made by Wi-Fi Direct, Bluetooth, Wireless Home Digital Interface, or the like. The receiver  8960   a  transmits a screen to be displayed on the transmitter  8960   b . Thus, an image on the receiver can be easily displayed on the transmitter. 
     When connected with the receiver  8960   a , the transmitter  8960   b  may notify the receiver  8960   a  that not only the information transmitted from the transmitter but also a password is needed for screen display, and refrain from displaying the transmitted screen if a correct password is not obtained. In this case, the receiver  8960   a  displays a password input screen  8960   d  or the like, and prompts the user to input the password. 
       FIG. 539  illustrates a situation where a screen of a transmitter  8961   c  is displayed on the transmitter  8960   b  via the receiver  8960   a . The terminal  8961   c  such as a notebook computer transmits information for connecting to the terminal  8961   c , or an ID associated with the information. The receiver  8960   a  receives the signal transmitted from the transmitter  8960   b  and the signal transmitted from the transmitter  8961   c , establishes connection with each of the transmitters, and causes the transmitter  8961   c  to transmit an image to be displayed on the transmitter  8960   b . The transmitters  8960   b  and  8961   c  may communicate directly, or communicate via the receiver  8960   a  or a router. Hence, even in the case where the transmitter  8961   c  cannot receive the signal transmitted from the transmitter  8960   b , an image on the transmitter  8961   c  can be easily displayed on the transmitter  8960   b.    
     The above-mentioned operation may be performed only in the case where the difference between the time at which the receiver  8960   a  receives the signal transmitted from the transmitter  8960   b  and the time at which the receiver  8960   a  receives the signal transmitted from the transmitter  8961   c  is within a predetermined time. 
     The transmitter  8961   c  may transmit the image to the transmitter  8960   b  only in the case where the transmitter  8961   c  receives a correct password from the receiver  8960   a.    
     (Example of Application to Position Estimation Using Wireless Access Point) 
       FIG. 540  is a diagram illustrating an example of application of a transmission and reception system in Embodiment 20. 
     A receiver  8963   a  such as a smartphone receives an ID transmitted from a transmitter  8963   b . The receiver  8963   a  obtains position information of the transmitter  8963   b  using the received ID as a key, and estimates the position of the receiver  8963   a  based on the position and direction of the transmitter  8963   b  in the captured image. The receiver  8963   a  also receives a signal from a radio wave transmitter  8963   c  such as a Wi-Fi access point. The receiver  8963   a  estimates the position of the receiver  8963   a , based on position information and radio wave transmission direction information of the radio wave transmitter  8963   c  included in the signal. The receiver  8963   a  estimates the position of the receiver  8963   a  by a plurality of means in this manner, and so can estimate its position with high accuracy. 
     A method of estimating the position of the receiver  8963   a  using the information of the radio transmitter  8963   c  is described below. The radio transmitter  8963   c  transmits synchronous signals in different directions, from a plurality of antennas. The radio transmitter  8963   c  also changes the signal transmission direction in sequence. The receiver  8963   a  estimates that a radio wave transmission direction in which the radio field intensity is highest is the direction from the radio transmitter  8963   c  to the receiver  8963   a . Moreover, the receiver  8963   a  calculates path differences from the differences in arrival time of radio waves transmitted from the different antennas and respectively passing through paths  8963   d ,  8963   e , and  8963   f , and calculates the distance between the radio transmitter  8963   c  and the receiver  8963   a  from radio wave transmission angle differences θ 12 , θ 13 , and θ 23 . By further using surrounding electric field information and radio wave reflector information, the receiver  8963   a  can estimate its position with higher accuracy. 
     (Position Estimation by Visible Light Communication and Wireless Communication) 
       FIG. 541  is a diagram illustrating a structure for performing position estimation by visible light communication and wireless communication. In other words,  FIG. 541  illustrates a structure for performing terminal position estimation using visible light communication and wireless communication. 
     A mobile terminal performs visible light communication with a light emitting unit, to obtain an ID of the light emitting unit. The mobile terminal inquires of a server using the obtained ID, and obtains position information of the light emitting unit. An actual distance L 1  can be obtained as a result. Moreover, since a tilt θ 1  of the mobile terminal is detectable using a gyroscope or the like as already described in other embodiments, L 3  can be calculated. The use of L 1  and L 3  enables calculation of the value of x1 of the mobile terminal. 
     Regarding the value of y1, position estimation is performed using wireless communication. In the case where beamforming is performed from an MIMO access point toward the mobile terminal, a beamforming angle θ2 is set by the MIMO access point and is a known value. Accordingly, by obtaining the beamforming angle θ2 by wireless communication or the like, the mobile terminal can calculate the value of y1 from x1 and θ2. MIMO is capable of forming a plurality of beams, and so a plurality of beamformings may be used for position estimation of higher accuracy. 
     As described above, according to this embodiment, the position estimation accuracy can be enhanced by employing both the position estimation by visible light communication and the position estimation by wireless communication. 
     Though the information communication method according to one or more aspects has been described by way of the embodiments above, the present disclosure is not limited to these embodiments. Modifications obtained by applying various changes conceivable by those skilled in the art to the embodiments and any combinations of structural elements in different embodiments are also included in the scope of one or more aspects without departing from the scope of the present disclosure. 
       FIG. 542A  is a flowchart of an information communication method according to an aspect of the present disclosure. 
     An information communication method according to an aspect of the present disclosure is an information communication method of obtaining information from a subject, and includes steps SK 91  to SK 93 . 
     In detail, the information communication method includes: a first exposure time setting step SK 91  of setting a first exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a plurality of bright lines corresponding to a plurality of exposure lines included in the image sensor appear according to a change in luminance of the subject; a first image obtainment step SK 92  of obtaining a bright line image including the plurality of bright lines, by capturing the subject changing in luminance by the image sensor with the set first exposure time; and an information obtainment step SK 93  of obtaining the information by demodulating data specified by a pattern of the plurality of bright lines included in the obtained bright line image, wherein in the first image obtainment step SK 92 , exposure starts sequentially for the plurality of exposure lines each at a different time, and exposure of each of the plurality of exposure lines starts after a predetermined blank time elapses from when exposure of an adjacent exposure line adjacent to the exposure line ends. 
       FIG. 542B  is a block diagram of an information communication device according to an aspect of the present disclosure. 
     An information communication device K 90  according to an aspect of the present disclosure is an information communication device that obtains information from a subject, and includes structural elements K 91  to K 93 . 
     In detail, the information communication device K 90  includes: an exposure time setting unit K 91  that sets an exposure time of an image sensor so that, in an image obtained by capturing the subject by the image sensor, a plurality of bright lines corresponding to a plurality of exposure lines included in the image sensor appear according to a change in luminance of the subject; an image obtainment unit K 92  that includes the image sensor, and obtains a bright line image including the plurality of bright lines by capturing the subject changing in luminance with the set exposure time; and an information obtainment unit K 93  that obtains the information by demodulating data specified by a pattern of the plurality of bright lines included in the obtained bright line image, wherein exposure starts sequentially for the plurality of exposure lines each at a different time, and exposure of each of the plurality of exposure lines starts after a predetermined blank time elapses from when exposure of an adjacent exposure line adjacent to the exposure line ends. 
     In the information communication method and the information communication device K 90  illustrated in  FIGS. 542A and 542B , the exposure of each of the plurality of exposure lines starts a predetermined blank time after the exposure of the adjacent exposure line adjacent to the exposure line ends, for instance as illustrated in  FIG. 24D . This eases the recognition of the change in luminance of the subject. As a result, the information can be appropriately obtained from the subject. 
     It should be noted that in the above embodiments, each of the constituent elements may be constituted by dedicated hardware, or may be obtained by executing a software program suitable for the constituent element. Each constituent element may be achieved by a program execution unit such as a CPU or a processor reading and executing a software program stored in a recording medium such as a hard disk or semiconductor memory. For example, the program causes a computer to execute the information communication method illustrated in the flowchart of  FIG. 542A . 
     An information communication method according to an aspect of the present disclosure is also applicable as in the following example. 
       FIG. 543  is a diagram illustrating a watch including light sensors. 
     A collecting lens is placed on the top surface of each sensor, as illustrated in the cross sectional view. In  FIG. 543 , the collecting lens has a predetermined tilt. The shape of the collecting lens is not limited to this, and may be any other shape capable of collecting light. With this structure, the light sensor can collect and receive light from a light source in the external world, by the lens. Even a small light sensor as included in a watch can thus perform visible light communication. In  FIG. 543 , the watch is divided into 12 areas and 12 light sensors are arranged in the areas, with the collecting lens being placed on the top surface of each light sensor. By dividing the inside of the watch into a plurality of areas and arranging a plurality of light sensors in this way, it is possible to obtain information from a plurality of light sources. For example, in  FIG. 543 , a first light sensor can receive light from a light source  1 , and a second light sensor can receive light from a light source  2 . A solar cell may be used as a light sensor. The use of a solar cell as a light sensor enables solar power to be generated and also visible light communication to be performed by a single sensor, which contributes to lower cost and a more compact shape. Moreover, in the case where a plurality of light sensors are arranged, information from a plurality of light sources can be obtained simultaneously, with it being possible to improve the position estimation accuracy. Though this embodiment describes a structure of providing light sensors in a watch, this is not a limit for the present disclosure, and any movable device such as a mobile phone or a mobile terminal is available. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to an information communication device and the like, and in particular to an information communication device and the like used for a method of communication between a mobile terminal such as a smartphone, a tablet terminal, a mobile phone, a smartwatch, or a head-mounted display and a home electric appliance such as an air conditioner, a lighting device, a rice cooker, a television, a recorder, or a projector.