Abstract:
An information transmission system includes: an information sending device including a light emitting section that emits light in a plurality of colors, a modulating section that modulates information to be transmitted into signals composed of changes in color, and a light emission control section that controls the light emitting section to emit light while changing color temporally based on the signals generated by the modulating section; and a receiving device including a camera that captures an image having color, and a control and communication section that detects a temporal color change of the light emitting section emitting light by light emission control by the information transmitting device, from images consecutively captured by the camera, decodes the detected color change into information, and outputs the generated information to a display section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Divisional of U.S. application Ser. No. 13/528,403, filed Jun. 20, 2012, which is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2011-139213 and No. 2011-139233, both filed Jun. 23, 2011, the entire contents of all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an information transmission system, an information sending device, an information receiving device, an information transmission method, an information sending method, an information receiving method, and a program product using a spatial optical transmission technology. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, so-called digital signage is gaining attention as an information transmission system using a spatial optical transmission technology. The digital signage refers to a system for transmitting information in a location other than home, such as outdoors, transportation facilities, storefronts, and public facilities, using a display device connected to a network. 
         [0006]      FIG. 1  is a diagram showing the use of the digital signage. In  FIG. 1 , an outdoor scene  100  is shown in the center, which includes pedestrians  101  and vehicles  102 , as well as buildings  103  to  105  located in the background. In particular, the building  104  in the center has a large-scale display terminal  106  mounted on a wall surface thereof. 
         [0007]    The display terminal  106  is a display device for digital signage that visualizes and displays information  107  transmitted from a server (not shown). This information  107  is, for example, information related to a certain product. In the example shown in  FIG. 1 , an image of a wristwatch is displayed as the product. 
         [0008]    In order to sell this product, the price, the sales period, the sales location, etc. need to be announced. 
         [0009]    In the example shown in  FIG. 1 , light modulation areas  1061  to  1064  are provided for the delivery of the above-described information. These modulation areas  1061  to  1064  are provided in portions (the four corners in  FIG. 1 ) of the screen of the display terminal  106 , and the required information is transmitted by time-serial changes of the light thereof. 
         [0010]    As a result, when people on the street catch sight of the display on the display terminal  106  and capture an image of the advertisement using his or her mobile electronic unit  108 , they can know detailed information related to the product, such as the price, the sales period and the sales location. 
         [0011]    In the case of the example shown in  FIG. 1 , a picture  110  of the product and a words balloon  111  containing detailed information on the product (information on discounts, such as 50% OFF, the discount period, such as from 11:00 to 15:00, and the like) are displayed on the screen  109  of the mobile electronic unit  108 . 
         [0012]    As types of spatial “optical” transmission technology, for example, the following are known. 
         [0013]    In U.S. Pat. No. 6,933,956, a technology for a spatial optical transmission system composed of a light transmitting unit and a light receiving unit is described. 
         [0014]    An overview of the technology is basically as follows: A light emitting unit logically determines a bit sequence that structures information to be transmitted; alternatively selects a bit pattern sequence from two pre-prepared bit pattern sequences having a low correlation with each other, based on the determination result; modulates the light in accordance with the selection result; and transmits the modulated light. A light-receiving unit receives the light and generates a binarized signal based on the intensity of the light; generates a logic signal 1 or a logic signal 0, when the bit pattern sequence included in the binarized signal corresponds to either one of the two bit pattern sequences; and reproduces the information included in the light. 
         [0015]    In Japanese Patent Application Laid-Open (Kokai) Publication No. 2005-267169, a technology is described which actualizes pointing by using flashing signals that are colored and have the same hue value. 
         [0016]    In Japanese Patent Application Laid-Open (Kokai) Publication No. 2006-072778, a technology is described in which four states are transmitted and received using prescribed changes in hue difference. 
         [0017]    In Japanese Patent Application Laid-Open (Kokai) Publication No. 2010-287820, a technology for actualizing high-speed communication is described in which, in addition to color changes, one of the colors is flashed at high speed, the light intensity is detected by a photodiode other than that of the image sensor being added, and thereby another signal is superimposed. 
         [0018]    In Japanese Patent Application Laid-Open (Kokai) Publication No. 2009-186203, a technology is described in which transmission is performed by a combination of light-emitting bodies in three colors. 
         [0019]    However, the technology described in U.S. Pat. No. 6,933,956 is merely a transmission technology based on the blinking of light which performs optical transmission using the logical signal 1 and the logical signal 0. Therefore, there is a problem in that, when signals (binary modulation signals) generated by binary blinking of light are received by a popularized camera having a common frame rate (about 30 fps) and information is reproduced, a considerable amount of time is required (about two seconds, described in detail hereafter). 
         [0020]    Although modulation of multivalued light using a combination of the colors red (R), green (G), and blue (B) as in the other known technologies can be performed to solve this problem, simply performing the value multiplexing increases processing load on the light receiving device. 
       SUMMARY OF THE INVENTION 
       [0021]    An object of the present invention is to enable the decoding of multivalued optical transmission information without increasing processing load. 
         [0022]    In order to achieve the above-described object, in accordance with one aspect of the present invention, there is provided an information transmission system comprising: an information sending device including a light emitting section which emits light in a plurality of colors, a modulating section which modulates information to be transmitted into signals composed of changes in color, and a light emission control section which controls the light emitting section to emit light while changing color temporally based on the signals generated by the modulating section; and an information receiving device including an imaging section which captures an image having color, a detecting section which detects a temporal color change of the light emitting section emitting light by light emission control by the light emission control section from images consecutively captured by the imaging section, a decoding section which decodes the color change detected by the detecting section into information, and an information output section which outputs the information generated by the decoding section. 
         [0023]    In accordance with another aspect of the present invention, there is provided an information sending device comprising: an image display section which has a light emitting section which emits light in a plurality of colors in pixel units; a modulating section which modulates information to be transmitted into signals composed of changes in color; and a light emission control section which controls a pixel area of the image display section to emit light while changing color temporally based on the signals generated by the modulating section. 
         [0024]    In accordance with another aspect of the present invention, there is provided an information receiving device comprising: an imaging section which captures an image having color; a detecting section which detects a pixel area whose color changes temporally from images consecutively captured by the imaging section; a decoding section which decodes color change detected by the detecting section into information; and an information output section which outputs the information generated by the decoding section. 
         [0025]    In accordance with another aspect of the present invention, there is provided an information transmission method comprising: a modulating step of modulating information to be transmitted into signals composed of changes in color; a light emission control step of controlling a light emitting section which emits light in a plurality of colors so that the light emitting section emits light while changing color temporally based on the signals generated in the modulating step; a detecting step of detecting a temporal color change of the light emitting section emitting light by light emission control in the light emission control step, from images consecutively captured by an imaging section which captures images having color; a decoding step of decoding the color change detected in the detecting step into information; and an information output step of outputting the information generated in the decoding step. 
         [0026]    In accordance with another aspect of the present invention, there is provided an information sending method comprising: a modulating step of modulating information to be transmitted into signals composed of changes in color; and a light emission control step of controlling a pixel area of an image display section having a light emitting section which emits light in a plurality of colors in pixel units, so as to emit light while changing color temporally based on the signals generated in the modulating step. 
         [0027]    In accordance with another aspect of the present invention, there is provided an information receiving method comprising: a detecting step of detecting a pixel area whose color changes temporally from images consecutively captured by an imaging section which captures an image having color; a decoding step of decoding color change detected in the detecting step into information; and an information output step of outputting the information generated in the decoding step. 
         [0028]    In accordance with another aspect of the present invention, there is provided a non-transitory computer-readable storage medium having stored thereon a program that is executable by a computer controlling an image display device having a light emitting section which emits light in a plurality of colors in pixel units, the program being executable by the computer to perform functions comprising: modulation processing for modulating information to be transmitted into signals composed of changes in color; and light emission control processing for controlling a pixel area of the image display device to emit light while changing color temporally based on the signals generated by the modulation processing. 
         [0029]    In accordance with another aspect of the present invention, there is provided a non-transitory computer-readable storage medium having stored thereon a program that is executable by a computer having an imaging section which captures an image having color, the program being executable by the computer to perform functions comprising: detection processing for detecting a pixel area whose color changes temporally from images consecutively captured by the imaging section; decode processing for decoding color change detected by the detection processing into information; and information output processing for outputting the information generated by the decode processing. 
         [0030]    The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a diagram showing the use of digital signage; 
           [0032]      FIG. 2  is a block diagram of an information transmission system according to an embodiment; 
           [0033]      FIG. 3A  is a diagram of modulation areas (light emitting section  5  [ 1061  to  1064 ]) in a lighted state; 
           [0034]      FIG. 3B  is a diagram of the modulation areas (light emitting section  5  [ 1061  to  1064 ]) in an unlighted state; 
           [0035]      FIG. 4  is a diagram of a signal format for optical communication according to the embodiment; 
           [0036]      FIG. 5  is a diagram of color separation characteristics in a color filter; 
           [0037]      FIG. 6  is a diagram in which the results in  FIG. 5  are converted to HSV space; 
           [0038]      FIG. 7  is a diagram of an encoding table: 
           [0039]      FIG. 8  is a flowchart of internal processing by a light receiving device  3 ; 
           [0040]      FIG. 9  is a sub-flowchart of Step S 3  in  FIG. 8 ; 
           [0041]      FIG. 10  is a sub-flowchart of Step S 4  in  FIG. 8 ; 
           [0042]      FIG. 11A  is a diagram showing an instance where the shape evaluation of a modulation area is performed by aspect ratio, in which the modulation area in the shape of a square is circumscribed within a square; 
           [0043]      FIG. 11B  is a diagram showing an instance where the shape evaluation of a modulation area is performed by aspect ratio, in which the modulation area having an irregular shape is circumscribed within a square; 
           [0044]      FIG. 11C  is a diagram showing an instance where the shape evaluation of a modulation area is performed by area filling ratio, in which the shape of the modulation area is substantially oval; 
           [0045]      FIG. 11D  is a diagram showing an instance where the shape evaluation of a modulation area is performed by area filling ratio, in which the shape of the modulation area is elongated oval; 
           [0046]      FIG. 12  is a diagram showing a buffering state of a buffer memory provided in a RAM  123 ; 
           [0047]      FIG. 13  is a diagram showing an example of a candidate area table; 
           [0048]      FIG. 14  is a sub-flowchart of Step S 7  in  FIG. 8 ; 
           [0049]      FIG. 15  is a sub-flowchart of Step S 72  in  FIG. 14 ; 
           [0050]      FIG. 16  is a diagram showing an image of the linking of area tables; 
           [0051]      FIG. 17  is a diagram showing a simplified image of the successively linked areas; 
           [0052]      FIG. 18  is a diagram showing an example of hue data extraction; 
           [0053]      FIG. 19  is an explanatory diagram of threshold setting; and 
           [0054]      FIG. 20  is a diagram showing an example of changes in hue value. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0055]    An embodiment of the present invention will be described with reference to the drawings. 
         [0056]      FIG. 2  is a block diagram of an information transmission system used in  FIG. 1 . In  FIG. 2 , the information transmission system  1  includes a light emitting device  2 , a light receiving device  3  and a service server  4 . 
         [0057]    The light emitting device  2  includes a light emitting section  5 , a storing section  6  that stores information such as tag identification (ID), and a modulating section  7  for modulation-driving the light emitting section  5  (equivalent to  1061  to  1064  in  FIG. 1 ) using information stored in the storing section  6 , and is provided in a system for transmitting information by a display terminal  106 , in locations such as outdoors, transportation facilities, storefronts, and public facilities. 
         [0058]    The light emitting section  5  transmits required information (such as tag ID) based on the manner of light emission by the light emitting section  5  (temporal color change of emitted light and color intensity). 
         [0059]    The light receiving device  3  is equivalent to a mobile electronic unit  108  in  FIG. 1 . This light receiving device  3  ( 108 ) is constituted by an optical system  8  including an imaging lens and the like, a camera  9 , an input sensor  10 , a display section  11  such as a liquid crystal display, a control and communication section  12 , etc. 
         [0060]    The service server  4  is, for example, a server that operates an information providing site or a product sales site (so-called online shop) on the Internet which is correlated to information transmitted by digital signage. 
         [0061]    The camera  9  is composed of a two-dimensional imaging device mounted with a color filter, such as a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). The camera  9  consecutively captures images within a predetermined viewing angle at a cycle of several tens of frames per second, and outputs the captured images to the control and communication section  12 . In this embodiment, the image-capturing cycle of the camera  9  is 30 frames per second (30 fps), taking the example of atypical (and also general-purpose) two-dimensional imaging device. The modulation frequency of the modulating section  7  of the light emitting device  2  is half of the image-capturing cycle, or in other words, 15 Hz. 
         [0062]    The input sensor  10  is, for example, a sensor for detecting various information inputted by user operation. Specifically, the input sensor  10  is a QWERTY keyboard including a numeric keypad or a touch panel. 
         [0063]    The display section  11  is a high-definition display device, such as a liquid crystal display. This display section  11  visualizes random information outputted accordingly from the control and communication section  12 , and outputs and displays the visualized information. 
         [0064]    The control and communication section  11  includes a communication interface that interfaces with the service server  4 , a computer or a microcomputer (hereinafter, referred to as a central processing unit [CPU])  121 , a read-only semiconductor memory (hereinafter, referred to as a read-only memory [ROM])  122 , and a writable/readable semiconductor memory (hereinafter, referred to as a random access memory [RAM])  123 . 
         [0065]    The control and communication section  12  is a control element for a program control system including peripheral circuits (not shown). This control and communication section  12  loads control programs prestored in the ROM  122  into the RAM  123 , and executes them by the CPU  121 . 
       [Modulation Method and Physical Format] 
       [0066]      FIG. 3A  and  FIG. 3B  are diagrams of modulation areas (light emitting section  5  [ 1601  to  1604 ]) provided in portions of the display terminal  106  for digital signage. As shown in  FIG. 3A , the light emitting section  5  ( 1601  to  1604 ) is expressed as a group composed of several pixels in a predetermined portion of the display terminal  106  (such as a corner of the terminal) for digital signage. 
         [0067]    The periphery of the light emitting section  5  ( 1601  to  1604 ) composed of 2×2 pixels is surrounded by a pixel frame (in this instance, a frame composed of 12 pixels labeled Bk) that enables the receiving device  3  ( 108 ) to differentiate the light emitting section  5  ( 1601  to  1604 ) from an image for digital signage. This pixel frame is composed of black pixels that are in an unlighted state at all times. 
         [0068]    For example, when all the pixels of the light emitting section  5  ( 1601  to  1604 ) are lit in red (R), the light emitting section  5  ( 1601  to  1604 ) enters the state shown in  FIG. 3A . When all the pixels of the light emitting section  5  ( 1601  to  1604 ) are unlit, the light emitting section  5  ( 1601  to  1604 ) is black (Bk) as shown in  FIG. 3B . 
         [0069]    Note that the shape and the number of pixels of the frame section are not limited to this example. 
         [0070]      FIG. 4  is a diagram of a signal format according to the present embodiment. 
         [0071]    In  FIG. 4 , the signal format  13  is constituted by a header section  131  composed of one non-luminous pulse (black), and a data section  132  composed of the subsequent nine pulses in which any one of the three colors red (R), blue (B), and green (G) is lit. Since the number of colors (three colors) of the data section  132  is three-valued (R, G, B) in contrast to the binary of black (unlighted) and white (lighted) described earlier, three-value modulation, so to speak, is performed in this example. 
         [0072]    The reason for using the single pulse in “black” in the header is that the luminance value of “black” is clearly and significantly different compared to other chromatic colors and therefore black is easier to separate without being affected by color mixing. 
         [0073]    Note that, although the three-value modulation using three colors including red, blue, and green is performed in  FIG. 4 , the present invention is not limited thereto and, for example, other three colors including cyan, magenta, and yellow may be used. Alternatively, seven colors in which white is added to these colors may be used. That is, multiple values exceeding three values may be used. 
         [0074]    The selection of color configuration (the number of values) to be used is mostly a matter of workshop modification. 
         [0075]    For example, a color configuration considered to be suitable based on the color separation characteristics, auto white balance (AWB) characteristics, or the like of the camera  9  may be used. 
         [0076]      FIG. 5  is a diagram of color separation characteristics of the light emitting section  5  ( 1601  to  1604 ) and the color filter of the camera  9 . 
         [0077]    As shown in  FIG. 5 , in actuality, slight amounts of the green wavelength component and the blue wavelength component are included even when only red is lighted. 
         [0078]    Therefore, in the present embodiment, the three primary colors, which are red, blue, and green and relatively separable, are used. 
         [0079]      FIG. 6  is a diagram in which the color space in  FIG. 5  is converted to hue, saturation, and value (HSV). 
         [0080]      FIG. 6  indicates that red, green, blue, and the like that are chromatic colors have a certain saturation or more and, even when the luminance decreases, they can be easily separated and distinguished from black (unlighted). 
         [0081]    Accordingly, with the use of color modulation such as that according to the present embodiment, the following advantageous effect can be acquired. For example, when data amounting to 9 bits in the data section  132  is to be outputted, the rational number expression for this data section  132  is “3̂9” (i.e., 3 9 ) in three-color modulation. This “3̂9” is “19,683” in decimal notation, and this “19,683” is “100110011100011” in binary notation, or in other words, 15-bit numerical sequence. Therefore, 14 bits or more can be expressed by at least nine pulses. 
         [0082]      FIG. 7  is a diagram showing an encoding chart for converting data values to a light-emission signal sequence. 
         [0083]    This encoding chart is stored in advance in the ROM  122  of the control and communication section  12 . 
         [0084]    Encoding signals “1”, “2”, and “3” in the chart indicate “red”, “blue”, and “green”, respectively. 
         [0085]    Accordingly, “123” indicates that light is emitted in the order of “red to blue to green”. 
         [0086]    When an encoding signal is “132”, or in other words, when light is emitted in the order of “red to green to blue”, four types of encoding results are acquired. 
         [0087]    For example, in the encoding chart in  FIG. 7 , a first encoding result having no redundancy is “8”, and a second encoding result having low redundancy is “7”. A third encoding result having medium redundancy is “7”, and a fourth encoding result having high redundancy is “2”. 
         [0088]    Here, the first encoding having no redundancy is provided with 27 values, from 1 to 27. 
         [0089]    The second encoding having low redundancy is provided with 24 values, from 1 to 24. 
         [0090]    The third encoding having medium redundancy is provided with 8 values, from 1 to 8. 
         [0091]    The fourth encoding having high redundancy is provided with 6 values, from 1 to 6. 
         [0092]    The first encoding can transmit more information at a significantly higher speed than conventional binary information transmission. However, when the control and communication section  12  receives this information (captures an image) by the camera  9 , a pixel area where the same color continues for a certain amount of time may be erroneously recognized as a part of a background image having no changes. 
         [0093]    The second encoding eliminates a state in which the light emission of the same color continues for a certain amount of time (in other words, only “111”, “222”, and “333”). 
         [0094]    In the third encoding, an initially identified color is used as a reference, the next color is far in distance from the hue of the initially identified color. 
         [0095]    In the fourth encoding, the colors of three consecutive pulses are different at all times, whereby noise of color existing in nature can be eliminated. 
         [0096]    Note that the selection of encoding is made based on the environment and characteristics of equipment in which the light emitting device  2  is arranged. 
         [0097]    Next, operations of the light receiving device  3  will be described. 
         [0098]      FIG. 8  is a diagram of internal processing performed by the overall light receiving device  3 . 
         [0099]    In the processing, first, the light receiving device  3  resets a frame counter in the RAM  123  (Step S 1 ), and stores a frame captured by the camera  9  in the RAM  123  (Step S 2 ). 
         [0100]    Next, the light receiving device  3  generates a binary image of the stored frame (Step S 3 ), and after creating a candidate area table in the RAM  123  (Step S 4 ), registers it in a list (Step S 5 ). 
         [0101]    Then, the light receiving device  3  judges whether or not the frame counter is a predetermined value n (Step S 6 ). When judged that the frame counter is not the predetermined value n, the light receiving device  3  returns to Step S 2 . When judged that the frame counter is the predetermined value n, the light receiving device  3  performs decode processing (Step S 7 ), and after performing information display processing (Step S 8 ), repeats Step S 1  and the subsequent steps. 
         [0102]    More specifically, at Step S 3 , the following processing is performed. 
         [0000]    [Candidate Area Detection Per Frame and Registration into Candidate Area Table] 
         [0103]    (a) Color Enhancement Correction Processing: 
         [0104]    As processing preceding HSV color space processing, color separation from RGB to R′G′B′ is performed on modulated light of the light emitting section  5  ( 1061  to  1064 ) by digital signage, using a conversion matrix such as that in the following expression (1). 
         [0105]    As a result of this processing, color having high saturation is further emphasized, and the separation is facilitated. 
         [0000]    
       
         
           
             
               
                 
                   
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         [0106]    The components a, b, and c in the matrix in expression (1) are, for example, values such as those in the following expression (2). In terms of vector space, the processing brings the values within the color space closer to the respective RGB axes. 
         [0000]        a =( a 11, a 22, a 33)=(−1.7,−0.65,−0.1)
 
         [0000]        b =( b 11, b 22, b 33)=(−0.9,1.9,−0.1)
 
         [0000]        c =( c 11, c 22, c 33)=(−0.1,−0.1,1.1)  (2)
 
         [0107]    (b) Conversion to HSV Color Space 
         [0108]    The saturation of the captured image is unaffected by the surrounding environment and is mostly unchanged. Conversely, the value of each color vector on which RGB decomposition has been performed has a characteristic of being affected by the surrounding environment. In order to address such characteristics in conventional luminance-based search, search is performed by conversion to an HSV color specification system, rather than expression in RGB. 
         [0109]    In the instance of the color modulation method and the color modulation indicated by the above-described physical format, the imaging results of the pulses in the data section have high saturation (S) values at all times, regardless of the color of the emitted light, even when the hue slightly fluctuates. 
         [0110]      FIG. 9  is a detailed diagram of the processing at Step S 3  in  FIG. 8 . 
         [0111]    As shown in  FIG. 9 , in the processing at Step S 3 , the light receiving device  3  converts the captured image in the RGB color space to an image in the HSV color space (Step S 31 ). Next, the light receiving device  3  sets a suitable threshold value for each pixel of an image expressed by the S (saturation) parameter (hereinafter, referred to as an S image), and an image expressed by the V (brightness: also referred to as I [intensity]) parameter (hereinafter, referred to as a V image) in the converted image expressed in the HSV color space, and binarizes them (Step S 32 ). 
         [0112]    The S image and the V image acquired thereby and a logical product thereof are set as a black and white binary image expressing a candidate for a communication area (Step S 33 ). 
         [0113]    [Labeling Processing] 
         [0114]    Next, labeling processing that is one of the characteristic features of the present embodiment will be described. 
         [0115]    In this processing, an image of an area where a light-modulated area excluding the header section  131  is included at all times and color characteristics coincidentally match is acquired as a black and white binary image. As a result, for example, an image is acquired in which an area having a high likelihood of color characteristics is white against a black background. 
         [0116]      FIG. 10  is a detailed diagram of the processing at Step S 4  in  FIG. 8 . 
         [0117]    As shown in  FIG. 10 , first, the light receiving device  3  performs a so-called labeling processing in which a continuous area and a basic shape parameter are identified (Step S 41 ). 
         [0118]    More specifically, the light receiving device  3  performs processing for identifying each continuous white area in the above-described candidate image and determining the shape information thereof. 
         [0119]    Note that, in the present embodiment, the gravity center of the area, the area (pixel area) thereof, and the coordinates of the four corners of the circumscribed quadrangle area thereof are acquired. 
         [0120]    In the subsequent processing, the light receiving device  3  extracts one of the acquired continuous areas (Step S 42 ) and performs filtering based on shape-related conditions. First, the light receiving device  3  eliminates areas that are too small (such as a 2×2-pixel square or smaller) in terms of area (area size) as noise (Step S 43 ). 
         [0121]    Next, the light receiving device  3  evaluates the shape of an area detected as a result of the labeling processing at Step S 41 . In the present embodiment, for simplification of the processing, the light receiving device  3  performs the evaluation based on the shape likelihood using the aspect ratio (Step S 44 ). 
         [0122]      FIG. 11A  to  FIG. 11D  are diagrams for explaining the shape evaluation of the modulation area. 
         [0123]      FIG. 11A  and  FIG. 11B  are diagrams showing the aspect ratio of the shape (white portion) of the modulation area. H is the long-side length of the circumscribed quadrangle of the shape of the modulation area, and W is the short-side length of the circumscribed quadrangle of the shape of the modulation area.  FIG. 11C  and  FIG. 11D  are diagrams showing the area filling ratio of the shape of the modulation area in relation to a predetermined area P (10×10 pixels in  FIG. 11C  and  FIG. 11D ). This area filling ratio is acquired by a value that is the area A of the shape (white portion) of the modulation area divided by the predetermined area P (10×10 pixels). 
         [0124]    As described above, conditions under which an area is considered to be a modulation area are set in advance regarding the aspect ratio and the area filling ratio, whereby areas that do not meet the conditions are not considered to be modulation areas (Step S 45 ). 
         [0125]    An area that has not been eliminated has a high possibility of being a modulation area, and therefore the light receiving device  3  registers it in the candidate area table (Step S 46 ). Subsequently, until it is judged that the processing has been completed on all candidate areas that may possibly be a modulation area (YES at Step S 47 ), the light receiving device  3  repeats the above-described Steps S 42  to S 45 . 
         [0126]    As a result, list entries for a required number of frames are acquired from Step S 1  to Step S 6 , and registered as a table list. 
         [0127]    However, because the phase relationship is indefinite, sampling by frames is twice the pulse cycle, or in other words, 30 fps in relation to 15 Hz-pulse-based modulation. Accordingly, since the number of pulses constituting a block is 10 pulses as described above, the list entries are n=2×10=20 and a buffering state is such as that shown in  FIG. 12  described hereafter. 
         [0128]    As described above, in the present embodiment, filtering based on shape-related conditions is performed for a modulation area, whereby shapes that are, for example, clearly different or clearly too small are eliminated in advance. Therefore, processing load related to the searching of an information light source area by the light receiving device  3  can be reduced. 
         [0129]    In the actual implementation thereof, when frame analysis is performed, and the current image-capturing condition (the surrounding environment, the state of camera shake, and the like) is clearly unsuitable for communication during the process of creating a candidate area table and adding to a table list, such as when the number of detected candidate areas is consecutively zero for a certain number of times, the processing can be reset during the process. 
         [0130]    [Filtering Processing for Decode Processing Candidate] 
         [0131]      FIG. 12  is a diagram showing a buffering state of a buffer memory provided in the RAM  123 . 
         [0132]    F0 to Fn in the upper portion are frames, and the tables in the lower portion indicate the buffering state of a candidate area table for each frame F0 to Fn. 
         [0133]    Note that a number of candidate area tables amounting to the n-number of frames (n is a natural number) are provided. When a predetermined number of frames is reached, the content is rewritten. 
         [0134]    The reason for providing a candidate area table for each frame is to significantly reduce the amount of calculation through use of compressed information as a candidate area table, rather than processing a large number of images in a time direction at a pixel data level, when processing time-series images. 
         [0135]    Here, an example of the candidate area table which is generated for each captured (imaged) frame will be described. 
         [0136]      FIG. 13  is a diagram showing an example of a candidate area table for frame number Fn=0. 
         [0137]    In  FIG. 13 , gravity center coordinates (cx, xy), area (size), and hue value (hue) are shown for each area No. (A). 
         [0138]    For example, gravity center coordinates (10,50), an area (70), and a hue value (80) are shown for area No. 0. 
         [0139]    Also, gravity center coordinates (111,321), an area (23), and a hue value (200) are shown for area No. 1. 
         [0140]    As described above, in the present embodiment, the gravity center coordinates (cx,xy) of an area subjected to labeling processing, the area (size) thereof, and the hue value (hue) thereof are successively stored in a candidate area table. 
         [0141]    Note that, in the description below, the identification of an individual candidate area is expressed as Fn:Am, and the identification of its internal parameter is expressed as Fn:Am:(cx,cy). 
         [0142]    Also, in the present embodiment, the distance between two area gravity centers (x1,y1) and (x2,y2) is determined using area information. 
         [0143]    However, because the area is already a dimension that is the square of the coordinates, consideration is given to enable addition as an evaluation measure of the same dimension. 
         [0000]      √( x 2− x 1)̂2+( y 2− y 1)̂2+(√Size2−√Size1)̂2)  (3)
 
         [0144]    Expression (3) indicates that, after square root calculation is performed on the area, the distance calculation of ordinary vectors in three dimensions is performed. 
         [0145]    In actuality, expression (3) is operated within a range of relatively small threshold values (such as 0 to 10). Therefore, to obtain a similar evaluation value while reducing the calculation amount, such as squaring the entirety, expression (3) may be modified as the following expression (4). 
         [0000]      ( x 2− x 1)+( y 2− y 1)+√(Size2−Size1)  (4)
 
         [0146]    As a result of the calculation, it can be considered that “small evaluation value=same area” in similarity evaluation between modulation areas. 
         [0147]      FIG. 14  is a flowchart showing the details of the processing at Step S 7  in  FIG. 8 . 
         [0148]    In the flowchart, the light receiving device  3  inputs a candidate frame point of a processing target frame and a candidate frame point of a frame previously acquired for one to three frames into the above-described expression (4), and calculates the evaluation value. Next, the light receiving device  3  creates a link list of the candidate frame point of the processing target frame and the candidate frame point of the frame previously acquired for one to three frames, using the evaluation value (Step S 71 ). 
         [0149]    Next, the light receiving device  3  successively links the link list between the two frames, while interpolating frames in which a coordinate point is not present due to being black (non-light-emitting) as black data within a permitted range (two frames in this instance), and determines a chain of coordinate point groups running 18 frames (Step S 72 ). 
         [0150]    Next, the light receiving device  3  eliminates discontinuous link elements in which three frames have passed without the presence of a candidate point, and rearranges a collection of coordinate point groups amounting to 18 frames such that the beginning of the like is black (Step S 73 ). 
         [0151]    Next, the light receiving device  3  extracts a complete link area constituted by related coordinate point groups amounting to 18 frames (Step S 74 ). Then, the light receiving device  3  performs decode processing on a hue value (optical signal sequence) corresponding to each coordinate point (Step S 75 ), and judges whether or not a valid decoding result (decoding value) has been acquired (Step S 76 ). 
         [0152]    When judged that a valid decoding result has been acquired, the light receiving device  3  performs request queuing for coordinates and data to display system processing so that the word balloon  111  and the like are displayed (Step S 77 ). Next, the light receiving device  3  judges whether or not the processing has been completed for all candidate point groups amounting to 18 frames (Step S 78 ). Even when a valid decoding result is not acquired, the light receiving device  3  judges whether or not the processing has been completed for all candidate point groups amounting to 18 frames. In either case, when judged that the processing has not been completed for all candidate point groups amounting to 18 frames, the light receiving device  3  repeats Step S 74  and the subsequent steps. 
         [0153]      FIG. 15  is a flowchart showing the details of the processing at Step S 72 . 
         [0154]    In the flowchart, first, the light receiving device  3  defines a processing target frame Fx, and advances the processing target frame Fx by one in the forward direction in terms of time (Step S 721 ). Next, the light receiving device  3  extracts one area candidate Ax from the processing target frame Fx (Step S 722 ) and defines the processing target frame Fx as Fd=Fn+1 (Step S 723 ). 
         [0155]    Next, the light receiving device  3  calculates an evaluation value of the area candidate Ax and each element of the processing target frame Fd using the above-described expression (4) (Step S 724 ), and determines a smallest link combination based on the evaluation value (Step S 725 ). 
         [0156]    Next, the light receiving device  3  judges whether or not the evaluation value of the determined smallest link combination is equal to or less than a threshold set in advance (Step S 726 ). When judged that the evaluation value is not equal to or less than the threshold, the light receiving device  3  judges whether or not the current processing target frame Fd is the fn+3rd frame (Step S 728 ). When judged that the current processing target frame Fd is the fn+3rd frame, the light receiving device  3  judges that a linking area has not been found (Step S 729 ), and repeats Step S 722  and the subsequent steps. 
         [0157]    At Step S 728 , when judged that the current processing target frame Fd is not the fn+3rd frame, the light receiving device  3  inserts dummy data (“skip”) and advances the processing target frame Fd by one in the forward direction in terms of time (Step S 730 ). Then, the light receiving device  3  repeats Step S 724  and the subsequent steps. 
         [0158]    At Step S 726 , when judged that the evaluation value of the smallest link combination is equal to or less than the threshold set in advance, the light receiving device  3  registers the current list in the link list as an adjacent list (Step S 727 ), and judges whether or not the processing has been completed for all areas of the processing target frame (Step S 731 ). When judged that the processing has not been completed, the light receiving device  3  repeats the processing at Step S 722  and the subsequent steps. When judged that the processing has been completed, the light receiving device  3  judges whether or not evaluation of all frames has been completed (Step S 732 ). When judged that the evaluation has not been completed, the light receiving device  3  returns to Step S 721 . When judged that the evaluation has been completed, the light receiving device  3  ends the processing. 
         [0159]    Note that, in expression (4) of the present embodiment, an evaluation value of 30 or less is “considered the same”. 
         [0160]    In the physical format according to the present embodiment, when saturation and brightness are high, linking is performed. However, because a header (black) is included at all times, the linking of area tables per frame when the processing at  FIG. 15  is performed is as shown in  FIG. 16 . 
         [0161]      FIG. 16  is a link image of area tables. 
         [0162]    In this image, sections connected by solid lines indicate the linking status of each candidate area where visible optical communication is performed. 
         [0163]    On the other hand, the dotted lines indicate a status in which, although whether or not communication is being performed is not clearly determined, linking on an evaluation value level is judged to have been made. 
         [0164]    At Step S 73 , the determined link is evaluated. In an area where a modulation signal is present at this time, a path (a connection of decoding results) that is linked over all 20 frames is present at all times. Therefore, other areas are eliminated. 
         [0165]      FIG. 17  is a diagram showing a simplified image of areas judged to be successively linked. Images that have skipped the link are considered black (non-illuminated), and interpolated as having a saturation of 0. The hue data of area Am of other images are extracted, respectively. 
         [0166]      FIG. 18  is a diagram showing an example of hue data extraction when a hue value has a range of 0 to 360. In  FIG. 18 , only a hue value held in each candidate area element data (individual F0:A0 and the like) are arrayed, corresponding to the result rearranged as the final link candidates in  FIG. 17 . 
         [0167]    In this way, a candidate as a time-based link is determined from the color and shape candidates of a single frame. The optical signal value held by the link area in  FIG. 17  (when changed to hue value link, in the case of the present embodiment) becomes that shown in  FIG. 18 , if the hue value is considered to have a range of 0 to 360 as in typical definition. Areas judged to be in an unlighted state and skipped are considered to have a value that is clearly out of the hue value range (such as −1). 
         [0168]    Returning to the flowchart in  FIG. 14 , first, the CPU  121  eliminates link areas that cannot be present as modulation areas. These areas are candidate areas meeting a condition “the header section  131  (−1 state) is not present”. 
         [0169]    When 19 frames are sampled in the above-described physical format, a signal area always has one or two unlighted periods (due to phase relationship between signal pulse and frame capture timing). Therefore, an area where “one or two consecutive −1 does not occur only once” is eliminated (an area where −1 is still present after other values are removed from −1 is not considered to be a signal). 
         [0170]    The value sequence of an area meeting this condition is selected. For example, in the case of the example in  FIG. 18 , area No. 1 is eliminated because unlighted timing is not present. 
         [0171]    Next, the hue value sequence is cyclically shifted to start from one or two consecutive −1. 
         [0172]    The processing up to this point is the processing at Step S 73 . 
         [0173]    At Step S 74  and Step S 75 , the CPU  121  checks validity regarding modulation of each link result, selects a phase, and performs demodulation. 
         [0174]    [Threshold Setting] 
         [0175]      FIG. 19  is an explanatory diagram of threshold setting. 
         [0176]    As shown in  FIG. 19 , the threshold of a possible range of a color emitting pulse of a modulation signal is set on a hue axis, taking into consideration color characteristics on the camera side (including the effect of dynamic AWB control) and light source on the transmitting side. For example, the threshold of R is near 0 (or 360), the threshold of G is near 120, and the threshold of B is near 240. 
         [0177]    Note that, although the threshold is fixed in the present embodiment, the threshold may be dynamically optimized by being set in accordance with an environment matching the characteristics of the camera  9  or set in a valley between peaks in hue distribution. 
         [0178]    In addition, it is preferable that these threshold values are optimized for each light-emitting point, whereby a more stable reception can be performed even when receiving a plurality of light-emission signals having different color characteristics. 
         [0179]    As described above, a color that changes at 15 Hz (pulse cycle of 66 ms) is sampled at 30 fps by the camera  9 . Therefore, the 18 sample sequences can be considered to be constituted by two phases A and B. 
         [0180]    An example of change in hue value in which a peak considered to be an unlighted state comes at the beginning as described above is as follows. 
         [0181]      FIG. 20  is a diagram showing an example of change in hue value, in which the vertical axis is a hue value, the horizontal axis is a frame number, and phase A and phase B are arrayed along the horizontal axis. As shown in  FIG. 20 , the pattern of change in hue value varies. In this instance, phase A is comparatively an optimal phase, and the color changes at phase B at all times. 
         [0182]    Regarding a phase relationship with the light source, a value within the thresholds may be acquired in phase A and phase B. For example, in transition from R near zero to B, the intermediate value is near 300 between B and R, rather than G. Conversely, in transition from R near 340 to G, the intermediate value is near 60 of Y, rather than phase B. 
         [0183]    In either case, when the area candidate is a modulation signal, either of the phase A sequence and the phase B sequence is within the value range thresholds at all times. 
         [0184]    By the above-described processing, the area where the communication is being made has been determined, and the change in optical signals at an observation value level has been expressed by a color information row that can be applied to a decoding table. Next, when the color information row is collated with the decoder table in  FIG. 7 , transmission bit data is acquired. 
         [0185]    A noise area where saturation, spatial shape, time-based linking and the like coincidentally match is, of course, eliminated based on the rule in  FIG. 7  regarding redundancy. Therefore, it is highly unlikely that changes in nature are coincidentally taken as data. 
         [0186]    In the processing of the present embodiment, changes in nature may coincidentally match. Accordingly, it is preferable that reception error is prevented by error detection, correction, and the like for the higher-order layers. 
         [0187]    As a result, the following effects can be achieved by the present embodiment. 
         [0188]    A. Since the optical transmission method is used in which color modulation is performed by at least three-values, and 3 9  is equal to or greater than 14 bits in, for example, three-color modulation, 14 bits or more can be expressed in nine pulses, whereby transmitting time can be shortened. 
         [0189]    B. In the decoding processing for image sensor communication, table-based time-direction processing of frames is performed. Therefore, the amount of processing to be handled can be significantly reduced. 
         [0190]    C. Time-based change in an area is made by the center of gravity and size change. Therefore, link judgment having a high degree of relevance can be performed. 
         [0191]    D. The transmitting side performs repeated transmissions of a fixed length. Therefore, rather than finding a header and starting sampling for communication, data amounting to a data block length is stored and a header is retrieved from the stored data. As a result, response time for communication acquisition can be minimized. 
         [0192]    E. The detection of a modulation area is performed after filtering based on shape conditions, such as the elimination of shapes that are clearly different or too small, being performed. Therefore, processing load on the light receiving device  3  related to the searching of an information light source can be reduced. 
         [0193]    While the present invention has been described with reference to the preferred embodiments, it is intended that the invention be not limited by any of the details of the description therein but includes all the embodiments which fall within the scope of the appended claims.