Patent Publication Number: US-2023141877-A1

Title: Image display method of display device, image display method of display system, and display device

Description:
The present application is based on, and claims priority from JP Application Serial No. 2021-181874, filed Nov. 8, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an image display method of a display device, an image display method of a display system, and the display device. 
     2. Related Art 
     There has been known a technique for enabling a display device and an interface device to be attached and detached. For example, a projection system disclosed in JP-A-2006-208832 (Patent Literature 1) includes a projector attachable to and detachable from a pedestal device. The pedestal device includes a tuner that transmits an image signal and a voice signal and a connecting unit that electrically connects the projector and the tuner. The pedestal device transmits the image signal and the voice signal to the projector. 
     In a configuration in which the display device is attachable and detachable as described in Patent Literature 1, the transmission of the image signal is discontinued by detaching the display device. In this case, since display based on the image signal is interrupted, operation of a user is required in order to resume the display, which is time-consuming. 
     SUMMARY 
     An aspect of the present disclosure is directed to an image display method of a display device, the image display method including: displaying a first image based on a first image signal received by wired communication; and, when detecting a state in which the first image signal by the wired communication cannot be received, starting displaying a second image based on a second image signal received by wireless communication. 
     Another aspect of the present disclosure is directed to an image display method of a display system, the image display method including: when an interface device is wire-connected to a display device, transmitting a first image signal from the interface device to the display device by wired communication; displaying, with the display device, a first image based on the first image signal received by the wired communication; and, when the display device detects a state in which the first image signal by the wired communication cannot be received, starting displaying a second image based on a second image signal received by wireless communication. 
     Still another aspect of the present disclosure is directed to a display device including a display unit, the display device executing: displaying a first image based on a first image signal received by wired communication; and, when detecting a state in which the first image signal by the wired communication cannot be received, starting displaying a second image based on a second image signal received by wireless communication. 
     Still another aspect of the present disclosure is directed to a display system including: a display device including: a display unit; a first connecting unit including a connection terminal and configured to receive a first image signal by wired communication through the connection terminal; a second connecting unit configured to receive a second image signal by wireless communication; and a display control unit; and an interface device including: a signal input unit to which a third image signal is input; a first transmitting unit connected to the connection terminal of the display device and configured to transmit the first image signal by the wired communication through the connection terminal; a second transmitting unit configured to execute wireless communication with the second connecting unit of the display device and transmit the second image signal by the wireless communication; and a transmission control unit. The transmission control unit executes at least one of an operation for transmitting the first image signal from the first transmitting unit based on the third image signal input to the signal input unit and an operation for transmitting the second image signal from the second transmitting unit based on the third image signal input to the signal input unit. The display control unit causes the display unit to display a first image based on the first image signal received by the first connecting unit and, when detecting a state in which the first image signal cannot be received by the first connecting unit, causes the display unit to start displaying a second image based on the second image signal received by the second connecting unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an exterior view of a projector and an interface device. 
         FIG.  2    is a block diagram showing a configuration example of a control system of a projection system. 
         FIG.  3    is a sequence chart showing an operation of the projection system. 
         FIG.  4    is a sequence chart showing an operation of the projection system. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     1. Configurations of a Projector and an Interface Device 
       FIG.  1    is an exterior view of a projector  1  and an interface device  2  according to a first embodiment. The projector  1  and the interface device  2  are coupled to each other and configure a projection system  100 . The projection system  100  corresponds to an example of the display system. 
     The projector  1  projects image light PL toward a projection target and forms an image on the projection target. The projector  1  corresponds to an example of the display device. The projector  1  projecting the image light PL is equivalent to displaying an image on the projection target. This operation is referred to as display in the following explanation. The image includes a video and a still image. 
     The projector  1  is attachable to and detachable from the interface device  2 . The projector  1  can display an image in a state in which the projector  1  is coupled to the interface device  2 . The projector  1  can display an image in a state in which the projector  1  is separated from the interface device  2 . 
     The interface device  2  is set on the upper surface of a desk or a cabinet. The projector  1  is placed on an upper surface  21  of the interface device  2  in the state in which the projector  1  is coupled to the interface device  2 . A protrusion  22  is provided on the upper surface  21 . A connection terminal  23  is disposed in the protrusion  22 . 
     A recess  45  is formed on the bottom surface of the projector  1 . The recess  45  fits with the protrusion  22  in a state in which the projector  1  is placed on the upper surface  21 . The protrusion  22  having a prism shape shown in  FIG.  1    is an example. A shape and a size of the protrusion  22  can be optionally changed. A shape and a size of the recess  45  only have to be a shape and a size with which a space capable of housing the protrusion  22  can be formed. 
     A connection terminal  46  is disposed in the recess  45 . The connection terminal  46  is in contact with the connection terminal  23  in a state in which the projector  1  is set on the upper surface  21  of the interface device  2 . The connection terminal  23  and the connection terminal  46  are electric contacts made of metal or another conductor. The connection terminal  23  and the connection terminal  46  come into contact with each other to thereby electrically connect the projector  1  and the interface device  2 . The projector  1  and the interface device  2  transmit image signals via the connection terminal  23  and the connection terminal  46  as explained below. 
     An image source  3  is connected to the interface device  2 . The image source  3  is a device that outputs an image signal. The image source  3  may be an image output device such as a media player or a digital camera. Examples of the image source  3  include information processing terminals such as a personal computer, a smartphone, and a tablet terminal. 
     The interface device  2  includes a connector  24 . A connector  5  formed at the distal end of a cable  4  for electrically connecting the interface device  2  and the image source  3  can be connected to the connector  24 . 
     The connector  24  and the connector  5  are connectors conforming to a standard concerning image signal transmission. Examples of the standard concerning image signal transmission include HDMI (High-Definition Multimedia Interface), USB (Universal Serial Bus)-Type C, DisplayPort, HDBaseT, and DVI (Digital Visual Interface). However, the standard concerning image signal transmission may be other standards. HDMI, DisplayPort, and HDBaseT are respectively registered trademarks. 
     The connector  24  and the connector  5  maybe a terminal for inputting and outputting an analog image signal such as an RCA terminal, a VGA terminal, an S terminal, and a D terminal. The interface device  2  may include a plurality of connectors  24 . In this case, types and standards of the plurality of connectors  24  may be different. 
     The interface device  2 , the image source  3 , and the cable  4  are preferably capable of transmitting and receiving a control signal between the interface device  2  and the image source  3 . The control signal is, for example, a signal for the interface device  2  to instruct the image source  3  to temporarily stop and resume an image output. In this embodiment, an example is explained in which the cable  4  is an HDMI cable and the connector  24  and the connector  5  conform to the HDMI standard. In this configuration, the interface device  2  and the image source  3  can transmit and receive the control signal with a CEC (Consumer Electronics Control) link. 
     2. Configuration of a Control System of the Projection System 
       FIG.  2    is a block diagram showing a configuration example of a control system of the projection system  100 . As explained above, the projection system  100  includes the projector  1  and the interface device  2 . In  FIG.  2   , a screen SC is shown as a projection target of the projector  1 . However, a direction in which the projector  1  projects the image light PL and the projection target are not limited. 
     The projector  1  includes a projection device  10  that projects the image light PL and a driving circuit  15  that drives the projection device  10 . The projection device  10  includes a light source  11 , a light modulation device  12 , and a projection optical system.  13 . The driving circuit  15  includes a light source driving circuit  16  and a light modulation device driving circuit  17 . 
     The light source  11  is a lamp light source such as a halogen lamp, a Xenon lamp, or an ultrahigh-pressure mercury lamp or a solid-state light source such as an LED (light Emitting Diode) or a laser light source. The light source driving circuit  16  lights and extinguishes the light source  11  according to control of a control device  50 . The light source driving circuit  16  adjusts luminance of the light source  11  according to the control of the control device  50 . 
     The light modulation device  12  includes a not-shown light modulation element. The light modulation element included in the light modulation device  12  includes, for example, a transmission-type liquid crystal panel. The light modulation element included in the light modulation device  12  may be a reflection-type liquid crystal panel or may be a digital micromirror device (DMD). 
     Light emitted by the light source  11  is separated into three color lights of red light, green light, and blue light by a not-shown optical element disposed on an optical path between the light source  11  and the light modulation device  12  and is made incident on the light modulation device  12 . The light modulation device  12  modulates the lights with the light modulation element to generate image lights PL. The image lights PL are combined by a combination optical system such as a cross dichroic prism and emitted to the projection optical system  13 . 
     The light modulation device driving circuit  17  is connected to an image processing unit  43 . The light modulation device driving circuit  17  drives the light modulation device  12  based on an image signal generated by the image processing unit  43  and draws an image on the light modulation element of the light modulation device  12  in frame units. 
     The projection optical system  13  includes a lens, a mirror, and the like for forming an image of the image light PL on the screen SC. The image light PL is projected onto the screen SC through the projection optical system  13  and causes the screen SC to form a projection image. The screen SC corresponds to an example of a projection surface. 
     The projector  1  includes an operation unit  31 , a remote controller light receiving unit  32 , an input interface  33 , a signal processing unit  35 , a microphone  36 , a speaker  37 , a first connecting unit  41 , a second connecting unit  42 , an image processing unit  43 , and a control device  50 . The input interface  33 , the signal processing unit  35 , the first connecting unit  41 , the second connecting unit  42 , the image processing unit  43 , and the control device  50  are connected to one another via a bus  39  to be capable of performing data communication. 
     The operation unit  31  includes various buttons and switches provided on a housing surface of the projector  1 . For example, the operation unit  31  includes a switch for instructing a start of a voice recognition function. The operation unit  31  generates an operation signal corresponding to operation of a button or a switch and outputs the operation signal to the input interface  33 . The input interface  33  includes a circuit that outputs the operation signal input from the operation unit  31  to the control device  50 . 
     The remote controller light receiving unit  32  includes a light receiving element that receives infrared light. The remote controller light receiving unit  32  receives an infrared signal transmitted from a remote controller  7 . When a not-shown switch included in the remote controller  7  is operated, the remote controller  7  transmits an infrared signal indicating the operation. The remote controller light receiving unit  32  decodes the received infrared signal to generate an operation signal. The remote controller light receiving unit  32  outputs the generated operation signal to the input interface  33 . The input interface  33  includes a circuit that outputs the operation signal input from the remote controller light receiving unit  32  to the control device  50 . 
     A specific form of signal transmission and reception between the remote controller  7  and the remote controller light receiving unit  32  is not limited. A configuration in which the remote controller  7  transmits the infrared signal to the remote controller light receiving unit  32  is an example. For example, a configuration may be adopted in which the remote controller  7  and the remote controller light receiving unit  32  transmit and receive signals by executing short-range wireless communication such as Bluetooth. In this case, the projector  1  may include, instead of the remote controller light receiving unit  32 , a communication processing circuit that executes the short-range wireless communication such as Bluetooth. Bluetooth is a registered trademark. 
     The signal processing unit  35  is connected to the microphone  36  and the speaker  37 . The microphone  36  collects sound on the outside of the housing of the projector  1 . The signal processing unit  35  converts voice collected by the microphone  36  into digital voice data and outputs the digital voice data to the control device  50 . The signal processing unit  35  drives the speaker  37  based on the digital voice data input from the control device  50  to thereby cause the speaker  37  to output sound. 
     The signal processing unit  35  may include a digital/analog conversion circuit that converts the digital voice data into an analog voice signal. The signal processing unit  35  may include an amplifier that amplifiers the analog voice signal. 
     The first connecting unit  41  is an interface device including the connection terminal  46  and an interface circuit that transmits and receives an image signal through the connection terminal  46 . In a state in which the connection terminal  23  and the connection terminal  46  are conducting, the first connecting unit  41  receives a first image signal DS 1  output by the interface device  2 . A signal format of the first image signal DS 1  is not limited and may be signal formats conforming to the various standards explained above or may be an unstandardized signal format. The first image signal DS 1  may include a voice signal. The first image signal DS 1  may include a control signal for controlling the operation of the projector  1  from the interface device  2 . The first connecting unit  41  may be capable of transmitting signals such as a control signal to the interface device  2  according to the control of the control device  50 . 
     The second connecting unit  42  is a wireless communication device wirelessly connected to the interface device  2 . The second connecting unit  42  includes, for example, an antenna, an RF (Radio Frequency) circuit, and a baseband circuit. The second connecting unit  42  receives a second image signal DS 2  from the interface device  2  by wireless communication. The second connecting unit  42  executes, for example, wireless communication conforming to a standard concerning image signal wireless transmission. Examples of the standard concerning image signal wireless transmission include WirelessHD, MIracast, Wi-Fi, and Bluetooth. However, the standard concerning image signal wireless transmission may be other standards. WirelessHD, MIracast, and Wi-Fi are registered trademarks. The second image signal DS 2  may include a voice signal. The second image signal DS 2  may include a control signal for controlling the operation of the projector  1  from the interface device  2 . The second connecting unit  42  may be capable of transmitting signals such as a control signal to the interface device  2  according to the control of the control device  50 . 
     The image processing unit  43  selects an image source according to the control of the control device  50 . Sources usable by the projector  1  shown in  FIG.  2    are the first image signal DS 1  received by the first connecting unit  41 , the second image signal DS 2  received by the second connecting unit  42 , and image data stored in a memory  53 . The image processing unit  43  acquires image data from the selected image source and executes image processing on the image data. The image processing executed by the image processing unit  43  is, for example, resolution conversion processing, geometric correction processing, digital zoom processing, and image correction processing for adjusting a tint and luminance of an image. The image processing unit  43  generates an image signal based on the image data after the image processing and outputs the image signal to the light modulation device driving circuit  17 . An image displayed by the projector  1  based on the first image signal DS 1  corresponds to an example of the first image. An image displayed by the projector  1  based on the second image signal DS 2  corresponds to an example of the second image. The first image and the second image may be the same image. That is, the first image signal DS 1  and the second image signal DS 2  may be signals for transmitting the same image through different transmission paths. 
     A not-shown frame memory may be connected to the image processing unit  43 . The frame memory is configured by, for example, an SDRAM (Synchronous Dynamic Random Access Memory). In this case, the image processing unit  43  loads image data acquired from a source in the frame memory. The image processing unit  43  executes the image processing on the image data loaded in the frame memory. 
     The image processing unit  43  can be configured by, for example, an integrated circuit. The integrated circuit is configured by, for example, an LSI (Large Scale Integration). More specifically, the image processing unit  43  is configured by an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or the like. For example, an FPGA (Field-Programmable Gate Array) is included in the PLD. An analog circuit may be included in a part of the configuration of the integrated circuit. A processor and the integrated circuit may be combined. The combination of the processor and the integrated circuit is called microcontroller (MCU), SoC (System-on-a-Chip), system LSI, chipset, and the like. 
     The projector  1  includes a battery  49 . The battery  49  incorporates a secondary battery such as a lithium ion battery or a metal-hydrogen battery and supplies electric power of the secondary battery to the units of the projector  1 . The projector  1  includes a not-shown charging connector and charges the battery  49  with electric power input to the charging connector from the outside. The projector  1  can cause the units including the projection device  10 , the driving circuit  15 , the second connecting unit  42 , the image processing unit  43 , and the control device  50  to operate with electric power of the battery  49 . Specifically, the projector  1  can project the image light PL with the electric power charged in the battery  49 . The charging connector may be provided in the first connecting unit  41 . For example, a terminal in a part of the connection terminal  46  is a power feed terminal that supplies electric power from the interface device  2  to the projector  1 . The battery  49  may be charged by the electric power supplied by the connection terminal  46 . 
     The control device  50  includes a processor  51  and a memory  53 . The memory  53  is a storage device that stores, in a nonvolatile manner, programs to be executed by the processor  51  and data. The memory  53  is configured by a magnetic storage device, a semiconductor storage element such as a flash ROM (Read Only Memory), or a nonvolatile storage device of another type. The memory  53  may include a RAM (Random Access Memory) configuring a work area of the processor  51 . The memory  53  stores data to be processed by the control device  50  and a control program  55  to be executed by the processor  51 . 
     The processor  51  is configured by a CPU (Central Processing Unit) or an MPU (Micro-processing unit). The processor  51  may be configured as a single processor. A plurality of processors may function as the processor  51 . The processor  51  maybe configured by an SoC integrated with a part or the entire memory  53  and/or other circuits. As explained above, the processor  51  may be configured by a combination of a CPU that executes a program and a DSP (Digital Signal Processor) that executes predetermined arithmetic processing. All of functions of the processor  51  may be implemented in hardware or may be configured using a programmable device. The processor  51  may also have functions of the image processing unit  43 . That is, the processor  51  may execute the functions of the image processing unit  43 . 
     The processor  51  executes the control program  55  stored by the memory  53  to thereby control the units of the projector  1 . The control device  50  corresponds to an example of the display control unit. 
     The processor  51  causes the image processing unit  43  to select a source and acquire image data of the selected source. The processor  51  controls the driving circuit  15  and causes the projection device  10  to project the image light PL based on an image signal output by the image processing unit  43  and display an image. 
     The memory  53  stores, for example, image data. When the image processing unit  43  selects the image data stored by the memory  53  as a source, an image based on the image data stored by the memory  53  is projected by the projection device  10 . 
     When the connection terminal  23  of the interface device  2  is electrically connected to the first connecting unit  41  of the projector  1 , the processor  51  causes the first connecting unit  41  to receive the first image signal DS 1  by wired communication. In a state in which the interface device  2  and the first connecting unit  41  are wire-connected, the processor  51  monitors disconnection of the wire connection of the interface device  2  and the first connecting unit  41 . The state in which the interface device  2  and the first connecting unit  41  are wire-connected corresponds to a state in which the first image signal can be received. When detecting that the wire connection of the interface device  2  and the first connecting unit  41  is disconnected, the processor  51  attempts connection to the interface device  2  with the second connecting unit  42 . A state in which the wire connection of the interface device  2  and the first connecting unit  41  is disconnected corresponds to a state in which the first image signal cannot be received. When the second connecting unit  42  and the interface device  2  are wirelessly connected, the processor  51  receives the second image signal DS 2  by wireless communication. 
     A specific operation for detecting disconnection of the wire connection of the interface device  2  and the first connecting unit  41  is not limited. The processor  51  only has to be able to detect that the first image signal DS 1  cannot be received from the interface device  2 . Specific examples 1 to 4 of a configuration in which the processor  51  detects disconnection of the wire connection are explained below. 
     Specific example 1: When the first image signal DS 1  received by the first connecting unit  41  is interrupted, the processor  51  detects that the wire connection is disconnected. Specifically, when an electric signal input to the connection terminal  46  of the first connecting unit  41  stops and a stop time exceeds a predetermined time and times out, the processor  51  detects that the wire connection is disconnected. 
     Specific example 2: The processor  51  monitors electric conduction of the connection terminal  23  and the connection terminal  46 . When detecting that the conduction is interrupted, the processor  51  detects that the wire connection is disconnected. When this method is adopted, if contacts for conduction check are provided in the connection terminal  23  and the connection terminal  46 , the processor  51  can more easily detect disconnection of the wire connection. 
     Specific example 3: In a configuration in which electric power is supplied from the connection terminal  23  to the first connecting unit  41 , by detecting that the power supply to the first connecting unit  41  is interrupted, the processor  51  detects that the wire connection is disconnected. This operation is useful in a configuration in which the battery  49  is charged by electric power input to the first connecting unit  41  as explained above. 
     Specific example 4: The projection system  100  includes a component that detects physical separation of the protrusion  22  of the interface device  2  and the recess  45  of the projector  1 . Specifically, the projector  1  includes, on the inside of the recess  45 , a sensor that detects fitting with the protrusion  22 . The sensor is, for example, a switch-type sensor that comes into contact with the protrusion  22  and operates or an optical or magnetic sensor that detects approach of the protrusion  22 . When detecting, based on a detection value of the sensor, that the protrusion  22  separates from the recess  45 , the processor  51  detects disconnection of the wire connection. 
     When detecting that the interface device  2  is wire-connected to the first connecting unit  41 , the processor  51  may start an operation for receiving, with the first connecting unit  41 , the first image signal DS 1  from the interface device  2  by wired communication. For example, the processor  51  executes the operation in a state in which the interface device  2  is wirelessly connected to the second connecting unit  42  and the interface device  2  is not connected to the first connecting unit  41 . In this operation, the processor  51  attempts wired communication between the first connecting unit  41  and the interface device  2 . When the wired communication is established, the processor  51  starts receiving the first image signal DS  1  by the wired communication. Further, the processor  51  may disconnect the wireless connection of the second connecting unit  42  and the interface device  2 . 
     The interface device  2  includes a first transmitting unit  201 , a second transmitting unit  202 , a signal input unit  203 , and a transmission control unit  210 . 
     The first transmitting unit  201  is an interface device including the connection terminal  23  and an interface circuit that transmits and receives an image signal through the connection terminal  23 . The first transmitting unit  201  transmits the first image signal DS 1  to the projector  1  in a state in which the connection terminal  23  and the connection terminal  46  are conducting. 
     The second transmitting unit  202  is a wireless communication device wirelessly connected to the projector  1 . The second transmitting unit  202  includes, for example, an antenna, an RF circuit, and a baseband circuit. The second transmitting unit  202  is wirelessly connected to the second connecting unit  42  by wireless communication and wirelessly transmits the second image signal DS 2  to the projector  1 . The second transmitting unit  202  only has to be configured to be capable of communicating with the second connecting unit  42  and executes, for example, wireless communication conforming to the various standards explained above concerning wireless transmission of an image signal. 
     The signal input unit  203  is an interface device including the connector  24  and an interface circuit that receives an image signal through the connector  24 . The signal input unit  203  receives, with the connector  24 , a third image signal DS 3  output by the image source  3  through the cable  4 . A signal format of the third image signal DS 3  is not limited and may be a signal format conforming to the various standards explained above or may be an unstandardized signal format. The third image signal DS 3  may include a voice signal. The third image signal DS 3  may be capable of transmitting and receiving a control signal for controlling an operation between the interface device  2  and the image source  3 . In this embodiment, the cable  4  is an HDMI cable and the third image signal DS 3  is a signal conforming to a HDMI format. The image source  3  transmits the third image signal DS 3  including a video and voice of the HDMI format to the interface device  2 . The signal input unit  203  transmits a control signal to the image source  3  according to control of the transmission control unit  210 . The control signal is, for example, a CEC command. 
     The transmission control unit  210  is connected to each of the first transmitting unit  201 , the second transmitting unit  202 , and the signal input unit  203 . 
     The transmission control unit  210  includes a processor  211  and a memory  213 . The memory  213  is a storage device that stores programs to be executed by the processor  211  and data in a nonvolatile manner. The memory  213  is configured by a magnetic storage device, a semiconductor storage element such as a flash ROM, or a nonvolatile storage device of another type. The memory  213  may include a RAM configuring a work area of the processor  211 . The memory  213  stores data to be processed by the transmission control unit  210  and a control program  215  to be executed by the processor  211 . 
     The processor  211  is configured by a CPU, an MPU, a microcomputer, or the like. The processor  211  may be configured by a single processor or a plurality of processors may be configured to function as the processor  211 . The processor  211  may be configured by an SoC integrated with a part or the entire memory  213  and/or other circuits. All of functions of the processor  211  may be implemented in hardware or may be configured using a programmable device. 
     The processor  211  executes the control program  215  stored by the memory  213  to thereby control the units of the interface device  2 . 
     The processor  211  receives the third image signal DS 3  with the signal input unit  203  and generates the first image signal DS 1  or the second image signal DS 2  based on the third image signal DS 3 . The first image signal DS 1  and the second image signal DS 2  may be the same signal as the third image signal DS 3 . This operation is effective in, for example, a configuration in which the first transmitting unit  201 , the second transmitting unit  202 , and the signal input unit  203  are adaptable to a common signal format. Examples of the configuration include a configuration in which all of the first transmitting unit  201 , the second transmitting unit  202 , and the signal input unit  203  conform to the HDMI standard. 
     The processor  211  may generate the first image signal DS 1  and the second image signal DS 2  by converting a frame frequency, resolution, and transmission speed of the third image signal DS 3 . The processor  211  may perform processing for generating image data from an image signal included in the third image signal DS 3  and generating the first image signal DS 1  and the second image signal DS 2  anew based on the generated image data. In this case, the processor  211  may perform the same processing for a voice signal included in the third image signal DS 3 . The processing is effective, for example, when the first transmitting unit  201  and the second transmitting unit  202  conform to a standard different from a standard of the signal input unit  203  or when an unstandardized signal format is adopted. 
     When the connection terminal  23  is wire-connected to the connection terminal  46 , the processor  211  controls the first transmitting unit  201  to connect the first connecting unit  41  of the projector  1  and the first transmitting unit  201 . The processor  211  controls the first transmitting unit  201  to output the first image signal DS 1  to the projector  1  from the first transmitting unit  201 . 
     The processor  211  monitors disconnection of the wire connection of the first transmitting unit  201  and the projector  1  in a state in which the first transmitting unit  201  and the first connecting unit  41  are wire-connected. When detecting that the wire connection of the first transmitting unit  201  and the projector  1  is disconnected, the processor  211  attempts connection to the projector  1  with the second transmitting unit  202 . When the second transmitting unit  202  and the projector  1  are wirelessly connected, the processor  211  transmits the second image signal DS 2  from the second transmitting unit  202  to the projector  1  by wireless communication. 
     A specific operation in which the processor  211  detects that the wire connection of the first transmitting unit  201  and the projector  1  is disconnected is not limited. The processor  211  only has to be able to detect a state in which the first image signal DS 1  cannot be transmitted. Specific examples of a configuration in which the processor  211  detects disconnection of the wire connection are explained. Specific examples 1 to 4 explained below respectively correspond to the specific examples 1 to 4 of the operation of the processor  51  explained above. 
     Specific example 1: When the first image signal DS 1  transmitted by the first transmitting unit  201  is interrupted, the processor  211  detects that the wire connection is disconnected. The first connecting unit  41  of the projector  1  transmits a response to the transmitting unit  201  at a frame period, a packet period, or other timing while the first transmitting unit  201  transmits the first image signal DS 1 . The processor  211  detects that the wire connection is disconnected when an electric signal input to the connection terminal  23  from the projector  1  stops and a stop time exceeds a predetermined time and times out. 
     Specific example 2: The processor  211  monitors electric conduction of the connection terminal  23  and the connection terminal  46 . When detecting that the conduction is interrupted, the processor  211  detects that the wire connection is disconnected. When this method is adopted, for example, if contacts for conduction check are provided in the connection terminal  23  and the connection terminal  46 , the processor  211  can more easily detect disconnection of the wire connection. 
     Specific example 3: In the configuration in which electric power is supplied from the connection terminal  23  to the first connecting unit  41 , by detecting a state in which the electric power supply to the first connecting unit  41  cannot be performed, the processor  211  detects that the wire connection is disconnected. For example, when detecting that a state of a load connected to the connection terminal  23  of the first transmitting unit  201  suddenly changes or a load is not connected to the connection terminal  23 , the processor  211  detects disconnection of the wire connection. This operation is effective in the configuration in which the first transmitting unit  201  supplies electric power for charging the battery  49  to the first connecting unit  41  as explained above. 
     Specific example 4: The projection system  100  includes a component that detects physical separation of the protrusion  22  of the interface device  2  and the recess  45  of the projector  1 . Specifically, the projection system  100  includes, in the protrusion  22 , a sensor that detects fitting with the surface of the recess  45 . The sensor is, for example, a switch-type sensor that comes into contact with the surface of the recess  45  and operates or an optical or magnetic sensor that detects approach of the recess  45 . When detecting based on a detection value of the sensor that the protrusion  22  separates from the recess  45 , the processor  211  detects disconnection of the wire connection. 
     The processor  211  may execute the operation corresponding to the wire connection of the projector  1  in a state in which the projector  1  is wirelessly connected to the second transmitting unit  202  and the projector  1  is not wire-connected to the first transmitting unit  201 . Specifically, when detecting that the projector  1  is wire-connected to the first transmitting unit  201 , the processor  211  may start an operation for transmitting the first image signal DS 1  from the first transmitting unit  201  by wired communication. In this operation, the processor  211  attempts wired communication between the first transmitting unit  201  and the projector  1  and, when the wired communication is established, starts transmitting the first image signal DS 1  by the wired communication. Further, the processor  211  may disconnect the wireless connection of the second transmitting unit  202  and the projector  1 . 
     A subject of an operation in the case in which the processor  211  starts, with the first transmitting unit  201 , wired communication with the projector  1  and an operation in the case in which the processor  211  is wirelessly connected to the interface device  2  by the second transmitting unit  202  is not limited. For example, in processing in which the projector  1  and the interface device  2  establish communication, the processor  51  may take the initiative in executing an operation and the processor  211  may operate according to control of the processor  51  or the processor  51  and the processor  211  may operate oppositely to this. The processor  51  and the processor  211  may respectively autonomously execute operations. 
     The memory  53  included in the projector  1  stores pairing data  56 . The pairing data  56  is identification information capable of identifying an individual interface device  2 . The pairing data  56  includes at least one of identification information of the interface device  2  connected by the first connecting unit  41  and identification information of the interface device  2  connected by the second connecting unit  42 . The pairing data  56  is generated according to operation of the remote controller  7  or the operation unit  31  in a state in which the interface device  2  is connected to the first connecting unit  41  or the second connecting unit  42 . 
     When the interface device  2  is wire-connected to the first connecting unit  41 , the processor  51  authenticates the interface device  2  based on whether identification information of the connected interface device  2  is included in the pairing data  56 . When the identification information of the interface device  2  connected to the first connecting unit  41  is included in the pairing data  56 , the processor  51  establishes wired communication with the interface device  2 . By establishing the wired communication, the processor  51  is capable of executing reception of the first image signal DS 1 . 
     When identification information of the interface device  2  to which wireless connection is attempted by the second connecting unit  42  is included in the pairing data  56 , the processor  51  establishes wireless communication between the second connecting unit  42  and the interface device  2 . 
     By using the pairing data  56  in this way, it is possible to limit an operation in the case in which the projector  1  is coupled to an unknown interface device  2  and wireless connection to the unknown interface device  2 . 
     The memory  213  included in the interface device  2  stores pairing data  216 . The pairing data  216  is identification information capable of identifying an individual projector  1 . The pairing data  216  includes at least one of identification information of the projector  1  connected by the first transmitting unit  201  and identification information of the projector  1  connected by the second transmitting unit  202 . The pairing data  216  is generated according to operation of the remote controller  7  or the operation unit  31  in a state in which the projector  1  is connected to the first transmitting unit  201  or the second transmitting unit  202 . 
     When the projector  1  is wire-connected to the first transmitting unit  201 , the processor  211  authenticates the projector  1  based on whether identification information of the connected projector  1  is included in the pairing data  216 . The processor  211  establishes wired communication with the projector  1  when the identification information of the projector  1  connected to the first transmitting unit  201  is included in the pairing data  216 . By establishing the wired communication, the processor  211  is capable of executing transmission of the first image signal DS 1 . 
     The processor  211  establishes wireless connection by the second transmitting unit  202  when identification information of the projector  1  to which the wireless connection is attempted by the second transmitting unit  202  is included in the pairing data  216 . Consequently, it is possible to limit an operation in the case in which an unknown projector  1  is coupled to the interface device  2  and wireless connection to the unknown projector  1 . 
     3. Operation of the Projection System 
       FIGS.  3  and  4    are sequence charts showing an operation of the projection system  100 . 
       FIG.  3    shows an operation in the case in which one or both of the projector  1  and the interface device  2  are turned on in a state in which the projector  1  is coupled to the interface device  2 . Steps SA 11  to SA 17  in  FIG.  3    indicate an operation of the projector  1  and are executed by the control device  50 . Steps SB 11  to SB 19  indicate an operation of the interface device  2  and are executed by the transmission control unit  210 . 
     In step SA 11 , the projector  1  detects that the interface device  2  is wire-connected to the first connecting unit  41 . In step SB 11 , the interface device  2  detects that the first transmitting unit  201  is connected to the projector  1 . At this time, the projector  1  and the interface device  2  are capable of executing wired communication according to steps SA 11  and SB 11 . 
     In step SA 11 , the projector  1  may execute, using the pairing data  56 , authentication for the interface device  2  connected to the first connecting unit  41 . The projector  1  may be configured to start wired communication with the interface device  2  when succeeding in the authentication. Similarly, in step SB 11 , the interface device  2  may execute, using the pairing data  216 , authentication for the projector  1  connected to the first transmitting unit  201 . The interface device  2  may be configured to start wired communication with the projector  1  when succeeding in the authentication. 
     When detecting in step SB 12  that the third image signal DS 3  is input to the connector  24  from the image source  3 , the interface device  2  shifts to step SB 13 . In step SB 13 , the interface device  2  starts, based on the third image signal DS 3 , transmitting the first image signal DS 1  by wired communication. 
     In step SA 12 , the projector  1  starts processing for receiving, by wired communication, the first image signal DS 1  transmitted by the interface device  2  and processing for displaying an image with the projection device  10  based on the received first image signal DS 1 . 
     After steps SA 12  and SB 13 , the projection system.  100  executes an operation for displaying, with the projector  1 , an image of the third image signal DS 3  input to the interface device  2  from the image source  3 . 
     In the following explanation, for example, operation for detaching the projector  1  from the interface device  2  is performed and the wire connection of the projector  1  and the interface device  2  is disconnected. 
     In step SA 13 , the projector  1  detects disconnection of the wire connection. In step SB 14 , the interface device  2  detects disconnection of the wire connection. Details of the operations in steps SA 13  and SB 14  are as explained above. 
     The interface device  2  shifts to step SB 15  and transmits a control signal to the image source  3  from the signal input unit  203 . The control signal transmitted in step SB 15  is a signal for instructing to stop the output of the third image signal DS 3  and is, for example, a CEC command for instructing a temporary stop of an image output or image reproduction. 
     In step SA 14 , the projector  1  attempts wireless connection by the second connecting unit  42 . In step SB 16 , the interface device  2  attempts wireless connection by the second transmitting unit  202 . When succeeding in mutual communication between the projector  1  and the interface device  2 , the projector  1  establishes wireless communication in step SA 15  and the interface device  2  establishes wireless communication in step SB 17 . 
     Instep SA 14 , the projector  1  may execute, using the pairing data  56 , authentication for equipment to which wireless connection is attempted. The projector  1  may be configured to establish wireless communication by the second connecting unit  42  when succeeding in the authentication. In step SB 16 , the interface device  2  may execute, using the pairing data  216 , authentication for equipment to which wireless connection is attempted. The interface device  2  may be configured to establish wireless communication by the second transmitting unit  202  when succeeding in the authentication. 
     When the wireless communication by the second connecting unit  42  is established, in step SA 16 , the projector  1  switches a source selected by the image processing unit  43  to the second connecting unit  42 . 
     When the wireless communication by the second transmitting unit  202  is established, in step SB 18 , the interface device  2  transmits a control signal to the image source  3 . The control signal transmitted in step SB 18  is a signal for instructing to resume the output of the third image signal DS 3  and is, for example, a CEC command for instructing resumption of the image output or the image reproduction. 
     Thereafter, when detecting in step SB 18  that the third image signal DS 3  is input to the connector  24  from the image source  3 , the interface device  2  shifts to step SB 19 . In step SB 19 , the interface device  2  starts, based on the third image signal DS 3 , transmitting the second image signal DS 2  by wireless communication. 
     In step SA 17 , the projector  1  starts processing for receiving, by wireless communication, the second image signal DS 2  transmitted by the interface device  2  and processing for displaying an image with the projection device  10  based on the received second image signal DS 2 . 
       FIG.  4    shows an operation in the case in which the projector  1  is coupled to the interface device  2  in a state in which the projector  1  is detached from the interface device  2  and the second image signal DS 2  is transmitted from the interface device  2  to the projector  1  by wireless communication. Steps SA 21  to SA 26  in  FIG.  4    indicate an operation of the projector  1  and are executed by the control device  50 . Steps SB 21  to SB 27  indicate an operation of the interface device  2  and are executed by the transmission control unit  210 . 
     In step SA 21 , the projector  1  detects that the interface device  2  is connected to the connection terminal  46  of the first connecting unit  41 . The projector  1  shifts to step SA 22  and starts wired communication with the interface device  2 . 
     In step SB 21 , the interface device  2  detects that the projector  1  is connected to the connection terminal  23  of the first transmitting unit  201 . The interface device  2  shifts to step SB 22  and transmits a control signal to the image source  3  from the signal input unit  203 . The control signal transmitted in step SB 22  is a signal for instructing to stop the output of the third image signal DS 3  and is, for example, a CEC command for instructing a temporary stop of an image output or image reproduction. The interface device  2  shifts to step SB 23  and starts wired communication with the projector  1 . 
     In step SA 23 , the projector  1  may execute, using the pairing data  56 , authentication for the interface device  2  connected to the first connecting unit  41 . The projector  1  maybe configured to establish wired communication by the first connecting unit  41  when succeeding in the authentication. In step SB 24 , the interface device  2  may execute, using the pairing data  216 , authentication for the projector  1  connected to the first transmitting unit  201 . The interface device  2  may be configured to establish wired communication by the first transmitting unit  201  when succeeding in the authentication. 
     After establishing the wired communication, instep SA 24 , the projector  1  switches a source selected by the image processing unit  43  to the first image signal DS 1  received by the first connecting unit  41 . 
     After establishing the wired communication, instep SB 25 , the interface device  2  transmits a control signal to the image source  3 . The control signal transmitted in step SB 25  is a signal for instructing to resume the output of the third image signal DS 3  and is, for example, a CEC command for instructing resumption of the image output or the image reproduction. 
     When detecting that the third image signal DS 3  is input to the connector  24  from the image source  3 , the interface device  2  shifts to step SB 26 . In step SB 26 , the interface device  2  starts, based on the third image signal DS 3 , transmitting the first image signal DS 1  by wired communication. 
     In step SA 25 , the projector  1  starts processing for receiving, by wired communication, the first image signal DS 1  transmitted by the interface device  2  and processing for displaying an image with the projection device  10  based on the received first image signal DS 1 . 
     In step SA 26 , the projector  1  ends the wireless communication with the interface device  2  by the second connecting unit  42 . In step SB 27 , the interface device  2  ends the wireless communication with the projector  1  by the second transmitting unit  202 . In steps SA 26  and SB 27 , the wireless connection of the projector  1  and the interface device  2  is disconnected. 
     The projector  1  and the interface device  2  may maintain the wireless connection even after the transmission of the second image signal DS 2  from the interface device  2  to the projector  1  is started. In this case, there is an advantage that the operations in steps SA 14  and SA 15  and SB 16  and SB 17  in  FIG.  3    are quickly performed when the wired connection of the projector  1  and the interface device  2  is disconnected. In this case, the projector  1  and the interface device  2  preferably stop the transmission and reception of the second image signal DS 2  without disconnecting the wireless communication. 
     4. Action in the Embodiment 
     As explained above, the image display method of the projector  1  explained in the embodiment includes displaying the first image based on the first image signal DS 1  received by wired communication. The image display method of the projector  1  includes, when detecting a state in which the first image signal DS 1  by the wired communication cannot be received, starting displaying the second image based on the second image signal DS 2  received by wireless communication. 
     Consequently, when the projector  1  becomes unable to receive the first image signal DS 1 , it is possible to start receiving the second image signal DS 2  and display an image with the projection device  10 . Accordingly, when the first image signal DS 1  is interrupted, it is possible to continue the display even if the user does not perform operation. 
     The image display method of the projector  1  may be a method of, when it becomes possible to receive the first image signal DS 1  by the wired communication while the second image is displayed, finishing displaying the second image and starting displaying the first image. In this case, the first image signal DS 1  is started to be received and an image based on the first image signal DS 1  is started to be displayed while the second image signal DS 2  is received and the image is displayed by the projection device  10 . Consequently, since the wired communication is used when the image can be transmitted by the wired communication, it is possible to receive an image signal in a communication path having higher stability. 
     The image display method of the projection system  100  includes, when the interface device  2  is wire-connected to the projector  1 , transmitting the first image signal DS 1  from the interface device  2  to the projector  1  by wired communication. The image display method of the projection system  100  includes displaying, with the projector  1 , the first image based on the first image signal DS 1  received by the wired communication. The image display method of the projection system  100  includes, when the projector  1  detects a state in which the first image signal DS 1  by the wired communication cannot be received, starting displaying the second image based on the second image signal DS 2  received by wireless communication. 
     Consequently, when the projector  1  becomes unable to receive the first image signal DS 1  from the interface device  2  by wired communication, it is possible to receive the second image signal DS 2  by wireless communication and display an image. Accordingly, when the first image signal DS 1  is interrupted, it is possible to continue the display even if the user does not perform operation. 
     The image display method of the projection system  100  may include transmitting the second image signal DS 2  from the interface device  2  to the projector  1  by wireless communication. In this case, when the first image signal DS 1  is interrupted, it is possible to continue transmitting an image from the interface device  2  to the projector  1 . 
     The image display method of the projection system  100  may include receiving the third image signal DS 3  with the interface device  2 . The transmitting the first image signal DS 1  from the interface device  2  to the projector  1  by wired communication may include transmitting the first image signal DS 1  with the interface device  2  based on the third image signal DS 3 . The transmitting the second image signal DS 2  from the interface device  2  to the projector  1  by wireless communication may include transmitting the second image signal DS 2  with the interface device  2  based on the third image signal DS 3 . 
     In this case, the interface device  2  transmits the first image signal DS 1  and the second image signal DS 2  to the projector  1  based on the third image signal DS 3 . Accordingly, even if the first image signal DS 1  is interrupted while an image based on the first image signal DS 1  is displayed, it is possible to continue to display an image based on the third image signal DS 3  by receiving the second image signal DS 2 . 
     The projector  1  disclosed in the embodiment includes the projection device  10  and executes displaying the first image based on the first image signal DS 1  received by wired communication. When detecting a state in which the first image signal DS 1  by the wired communication cannot be received, the projector  1  executes starting displaying the second image based on the second image signal DS 2  received by wireless communication. 
     Consequently, when the projector  1  becomes unable to receive the first image signal DS 1  from the interface device  2  by wired communication, it is possible to receive the second image signal DS 2  by wireless communication and display an image. Accordingly, when the first image signal DS 1  is interrupted, it is possible to continue the display even if the user does not perform operation. 
     The projection system  100  includes the projector  1  and the interface device  2 . The projector  1  includes the projection device  10  and the first connecting unit  41  that includes the connection terminal  46  and receives the first image signal DS 1  by wired communication through the connection terminal  46 . The projector  1  includes the second connecting unit  42  that receives the second image signal DS 2  by wireless communication and the control device  50 . The interface device  2  includes the signal input unit  203  to which the third image signal DS 3  is input and the first transmitting unit  201  that is connected to the connection terminal  46  of the projector  1  and transmits the first image signal DS 1  by wired communication through the connection terminal  46 . The interface device  2  includes the second transmitting unit  202  that is wirelessly connected to the second connecting unit  42  of the projector  1  and transmits the second image signal DS 2  by wireless communication and the transmission control unit  210 . The transmission control unit  210  executes at least one of an operation for transmitting the first image signal DS 1  from the first transmitting unit  201  based on the third image signal DS 3  and an operation for transmitting the second image signal DS 2  from the second transmitting unit  202  based on the third image signal DS 3 . The control device  50  displays, on the projection device  10 , the first image based on the first image signal DS 1  received by the first connecting unit  41 . When detecting a state in which the first image signal DS 1  cannot be received by the first connecting unit  41 , the control device  50  causes the projection device  10  to start displaying the second image based on the second image signal DS 2  received by the second connecting unit  42 . 
     Consequently, the projector  1  that displays an image with the projection device  10  can receive the first image signal DS 1  from the interface device  2  by wired communication and display an image based on the first image signal DS 1 . When the projector  1  becomes unable to receive the first image signal DS 1 , the projector  1  can receive the second image signal DS 2  by wireless communication and display an image based on the second image signal DS 2 . Accordingly, when the first image signal DS 1  is interrupted, it is possible to continue the display even if the user does not perform operation. 
     In the projection system  100 , when the projector  1  becomes unable to receive the first image signal DS 1  with the first connecting unit  41 , the transmission control unit  210  causes the signal input unit  203  to output an instruction to stop transmitting the third image signal DS 3 . For example, the interface device  2  transmits a CEC command from the signal input unit  203  to the image source  3 . Consequently, it is possible to stop an input of the third image signal DS 3  after the projector  1  becomes unable to receive the first image signal DS 1  with the first connecting unit  41 . That is, it is possible to stop an advance of the third image signal DS 3  in a state in which the projector  1  cannot perform display. Accordingly, it is possible to prevent display content from advancing before the projector  1  can start display. 
     5. Other Embodiments 
     The embodiment explained above is a preferred implementation mode of the present disclosure. However, the present disclosure is not limited to this and various modified implementations are possible within a range not departing from the gist of the present disclosure. 
     For example, in the embodiment, the configuration is illustrated in which the projector  1  and the interface device  2  are electrically connected by placing the projector  1  on the interface device  2 . In this configuration, by lifting the projector  1  from the interface device  2 , the projector  1  and the interface device  2  are uncoupled and the electric connection is disconnected. This configuration is an example. For example, the projector  1  and the interface device  2  may be electrically connected via a cable. In this case, by detaching the cable from the projector  1  or the interface device  2 , the electric connection, that is, wire connection of the projector  1  and the interface device  2  is disconnected. In this case as well, the operations shown in  FIGS.  3  and  4    can be applied. 
     For example, a relay device that amplifies and distributes an image signal may be interposed between the projector  1  and the interface device  2 . In this case, the projector  1  and the interface device  2  are electrically connected via the relay device. Specifically, the projector  1  and the relay device are electrically connected by a cable and a terminal. The interface device  2  and the relay device are electrically connected by a cable and a terminal. In this case, by detaching the cable that connects the projector  1  and the relay device or the cable that connects the interface device  2  and the relay device, the electric connection, that is, the wire connection of the projector  1  and the interface device  2  is disconnected. In this case as well, the operations shown in  FIGS.  3  and  4    can be applied. 
     In the embodiment, the projection system  100  that uses the projector  1  as the display device is explained as an example. However, the display system is not limited to the configuration including the projector  1  that functions as the display device and projects an image on the screen SC. For example, the display device may be a liquid crystal display including a liquid crystal display panel. The display device may be, for example, a display including a PDP (plasma display panel) or an organic EL (Electro-Luminescence) panel. The present disclosure can be applied to other various display devices. In this case, the liquid crystal display panel, the PDP, and the organic EL panel correspond to examples of the display unit. 
     The configuration of the projector  1  and the interface device  2  shown in  FIG.  2    indicates a functional configuration. A specific implementation form is not particularly limited. That is, hardware individually corresponding to the functional units does not always need to be implemented. It is also naturally possible to adopt a configuration in which one processor executes a program to realize functions of a plurality of functional units. A part of functions realized by software in the embodiment and the modification may be realized by hardware. A part of functions realized by hardware may be realized by software. 
     The processing units of the sequence charts of  FIGS.  3  and  4    are divided according to main processing contents in order to facilitate understanding of the processing of the processor  51  and the processor  211 . The present disclosure is not limited by a way of division and names of the processing units. The processing of the processor  51  and the processor  211  can be divided into a larger number of processing units according to processing contents or can be divided to such that one processing unit includes a large number of kinds of processing. The processing order of the flowcharts is not limited to the illustrated examples. 
     The control program  55  to be executed by the processor  51  can also be recorded in, for example, a recording medium readable by the projector  1 . As the recording medium, a magnetic or optical recording medium or a semiconductor memory device can be used. Specifically, examples of the recording medium include portable or stationary recording media such as a flexible disk, a CD-ROM (Compact Disk Read Only Memory), a DVD, a Blu-ray Disc, a magnetooptical disk, a flash memory, and a card-type recording medium. The control program  55  can be stored in a server device or the like. The display control method can be realized by the projector  1  downloading the control program  55  from the server device. The same applies to the control program  215  to be executed by the processor  211 . Blu-ray is a registered trademark.