Patent Publication Number: US-2012033048-A1

Title: 3d image display apparatus, 3d image playback apparatus, and 3d image viewing system

Description:
FIELD OF THE INVENTION 
     The present invention relates to a 3D image display apparatus, a 3D image playback apparatus, and a 3D image viewing system, more particularly to a technology for simplifying a transmission cable routed to transmit video data, which is the base data of 3D images, from a plurality of video cameras. 
     BACKGROUND OF THE INVENTION 
     A 3D image viewing system enables to recognize 3D images by using binocular parallax information (information of disparity between images recognized with right and left eyes). 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Unexamined Japanese Patent Applications Laid-Open No. 11-341518 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     A technical disadvantage of the systems conventionally available is a wiring complexity because different transmission cables are used to wire a plurality of video cameras provided to capture images through different angles so that image information, which is the base data of 3D images, is obtained. 
     According to the invention disclosed in Patent Document 1, a display device is placed horizontally so that a viewer can enjoy 3D images regardless of his positional relationship with the display device horizontally placed (regular position, position opposite to the regular position, or positions on lateral sides of the regular position). However, these systems still have the conventional problem of a wiring complexity resulting from multiple transmission cables. 
     The present invention was accomplished to solve the conventional problem, and a main object thereof is to simplify a transmission cable routed to transmit video data, which is the base data of 3D images, from a plurality of video cameras. 
     Means for Solving the Problem 
     To solve the conventional problem, the present invention provides a 3D image display apparatus, a 3D image playback apparatus, a 3D image viewing system configured as described below. 
     A 3D image display apparatus according to the present invention comprises: 
     a transmission-reception device configured to receive a video data which is base data of 3D images including a plurality of image informations from a 3D image playback apparatus through a transmission cable and generate an image signal based on the video data; 
     a display device configured to display thereon an image obtained from the image signal; and 
     a control signal output device configured to output a control signal to shutter glasses worn by a viewer of the display device, the control signal controlling light-penetration states in penetration units for both eyes provided in the shutter glasses, wherein 
     the transmission-reception device receives the video data from the 3D image playback apparatus through the single transmission cable and generates the image signal and a synchronizing signal based on the received video data, the synchronizing signal indicating which of the plurality of image informations is included in the image signal currently outputted, and 
     the control signal output device generates the control signal based on the synchronizing signal. 
     In the 3D image display apparatus thus configured, a single transmission cable is provided and connected to the transmission-reception device of the 3D image display apparatus, therefore, the transmission cable can be readily routed without any wiring complexity. Further, the apparatus can still display 3D images all the same when the viewer&#39;s posture wearing the shutter glasses is off balance. 
     Effect of the Invention 
     According to the present invention, wherein the 3D image display apparatus and the 3D image playback apparatus are connected to each other with a transmission cable, the transmission cable can be readily routed without any wiring complexity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an overall structure of a 3D image viewing system according to an exemplary embodiment 1 of the present invention. 
         FIG. 2  is a flow chart of processing steps by a reception device according to the exemplary embodiment 1. 
         FIG. 3  is a block diagram illustrating an overall structure of a 3D image viewing system according to an exemplary embodiment 2 of the present invention. 
         FIG. 4  is a correlative table of image informations of a plurality of positions and a viewing posture information, illustrating how a control signal inputted to shutter glasses is defined in the 3D image viewing system according to the exemplary embodiment 2. 
         FIG. 5  is a correlative table of the viewing posture information indicating viewers&#39; viewing postures and the image informations to be suitably selected for the respective postures in a playback-side transmission-reception device according to the exemplary embodiment 2. 
         FIG. 6  is a perspective view of an image pickup device of a conventional 3D image viewing system. 
         FIG. 7  is an illustration of an image display device of the conventional 3D image viewing system and examples of a viewer&#39;s viewing posture. 
         FIG. 8  is a block diagram illustrating an overall structure of the conventional 3D image viewing system. 
         FIG. 9  is a correlative table of viewing posture informations and image informations of a plurality of positions, illustrating how a control signal inputted to shutter glasses is defined in the conventional 3D image viewing system. 
     
    
    
     EXEMPLARY EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Before starting to describe exemplary embodiments of a 3D image viewing system according to the present invention, basic technical characteristics of a conventional 3D image viewing system are described referring to  FIGS. 6-9 .  FIG. 6  is a perspective view of an image pickup device of a conventional 3D image viewing system.  FIG. 7  illustrates in a perspective view an image display device of the conventional 3D image viewing system, devices accessory to the image display device, and examples of a viewer&#39;s viewing posture.  FIG. 8  is a block diagram illustrating an overall structure of the conventional 3D image viewing system.  FIG. 9  is a table illustrating details of a control signal S 4  outputted by a control signal output device  24 . The system described referring to  FIGS. 6-9  has a basic structure of any 3D image viewing system but is not configured according to the exemplary embodiments of the present invention. 
     As illustrated in  FIG. 6 , first-fourth video cameras V 1 , V 2 , V 3 , and V 4  are provided around a viewfinder  40  and secured to positions equally spaced from one another in upper, lower, right, and left directions. The viewfinder  40  and the four video cameras V 1 , V 2 , V 3 , and V 4  are all directed toward a photographic subject  50 . 
     As illustrated in  FIG. 7 , a first viewer U 1  and a second viewer U 2  are both seated substantially in front of a display screen of a display device  22 . The first viewer U 1  wearing first shutter glasses m 1  is facing the display screen with no tilt of his head relative to the display screen. The second viewer U 2  wearing second shutter glasses m 2  is facing the display screen with his head tilting through 90 degrees relative to the display screen. The shutter glasses include liquid crystal glasses having an electronic shutter configured to change the states of penetration units for right and left eyes to and from a light-penetrable state and a light-impenetrable state by controlling a liquid crystal shutter 
     The display device  22 , an example of which is a liquid crystal display, is provided with a viewing posture sensor  23  which detects the viewers&#39; viewing postures by detecting their postures relative to the display device  22  such as a tilt of the shutter glasses m 1 , m 2  worn by the viewer U 1 , U 2 , and a control signal output device  24  which controls the shutter glasses m 1  and m 2 . 
     The shutter glasses m 1  and m 2  are each provided with a transmission-reception device (not illustrated in the drawings) for measuring the postures of the viewers U 1  and U 2  relative to the display device  22  through wireless communication with the viewing posture sensor  23 . 
     The control signal S 4  outputted from the control signal output device  24  is in charge of a timing control for switching to and from the light-penetrable state and the light-impenetrable state in one or both of the two penetration units in each of the shutter glasses m 1  and m 2 . 
     As illustrated in  FIG. 8 , the 3D image viewing system has an image selector apparatus E 3 , the four video cameras V 1 -V 4 , display device  22 , viewing posture sensor  23 , control signal output device  24 , and first and second shutter glasses m 1  and m 2 . 
     The image selector apparatus E 3  selects one of images captured by the four video cameras V 1 -V 4  per frame and outputs the selected image in the form of an image signal S 1 . The image selector apparatus E 3  also outputs a synchronizing signal S 2  to the control signal output device  24 , the control signal S 2  indicating which of image informations P 1 -P 4  obtained by the four video cameras V 1 -V 4  corresponds to the image signal S 1  currently outputted. The display device  22  displays an image based on the image signal S 1 . 
     The four video cameras V 1 -V 4  and the image selector apparatus E 3  are interconnected with independent transmission cables C 1 -C 4 . The viewing posture sensor  23  generates a viewing posture information S 3  indicating the postures of the first and second viewers U 1  and U 2  relative to the display screen of the display device  22 , such as a tilt of the viewer&#39;s head, based on the signal received from the first and second shutter glasses m 1  and m 2 , and then outputs the generated viewing posture information S 3  to the control signal output device  24 . 
     The viewing posture information S 3  recited in this description includes information that enables to determine whether the head is tilting relative to the screen, more particularly, whether the posture has “no tilt”, “90-degree tilt to left”, “90-degree tilt to right”, or “180-degree tilt”. The direction where the viewer&#39;s head is tilting, right or left, indicates the direction where the head is tilting when the viewer is seen from the side of the display device  22 . The head of the second viewer U 2  tilting to “right” drawn in  FIG. 7  is tiling to “left” when seen from the side of the display device  22 , in which case the head of the second viewer U 2  is tilting to “left” according to the viewing posture information S 3 . 
     The control signal output device  24  generates and outputs the control signal S 4  for the first and second shutter glasses m 1  and m 2  both based on the synchronizing signal S 2  from the image selector apparatus E 3  and the viewing posture information S 3  from the viewing posture sensor  23 . 
     The control signal S 4  is a signal which controls the timing of switching to and from the light-penetrable state and the light-impenetrable state in the right and left penetration units of the shutter glasses m 1  and m 2  so that the viewers U 1  and U 2  can both watch 3D images. 
     In  FIG. 9 , details of the control signal S 4  outputted from the control signal output device  24  are tabulated. More specifically, the drawing is a correlative table of the four video cameras V 1 -V 4  identified by the synchronizing signal S 2  and the postures of the viewers U 1  and U 2  relative to the display device  22  identified by the viewing posture information S 3  (“no tilt”, “90-degree tilt to left”, “90-degree tilt to right”, or “180-degree tilt”), illustrating the timing control for switching to and from the light-penetrable state and the light-impenetrable state in one or both of the right and left penetration units of the shutter glasses m 1  and m 2 . 
     Next, an operation of the 3D image viewing system is described. 
     Example 1 
     First Viewer U 1   
     An operation when the first viewer U 1  is seated substantially in front of the display device  22  is described. The viewing posture sensor  23  detects the viewing posture of the first viewer U 1  from the relative posture of the first shutter glasses m 1 . Since the first viewer U 1  is facing the screen without tilting his head, the viewing posture sensor  23  determines that the viewing posture of the first viewer U 1  has “no tilt” and outputs the determined posture as the viewing posture information S 3  to the control signal output device  24 . 
     The control signal output device  24  generates the control signal S 4  based on the tabulated provisions of  FIG. 9  and outputs the generated control signal S 4  to the first shutter glasses m 1 . While the image information P 1  of the video camera V 1  is being displayed on the display device  22  for the first shutter glasses m 1  worn by the first viewer U 1  with “no tilt”, the control signal S 4  is outputted so that the penetration unit for left eye is made light-penetrable and the penetration unit for right eye is made light-impenetrable. While the image information P 3  of the video camera V 3  is being displayed on the display device  22 , the control signal S 4  is outputted so that the penetration unit for right eye is made light-penetrable and the penetration unit for left eye is made light-impenetrable. While the image informations P 2  and P 4  of the video cameras V 2  and V 4  are being displayed on the display device  22 , the control signal S 4  is outputted so that the penetration units for right and left eyes are both made light-impenetrable. 
     In the first shutter glasses m 1  worn by the first viewer U 1 , a liquid crystal shutter is controlled based on the control signal S 4 . Therefore, when the first viewer U 1  views the display device  22  through the first shutter glasses m 1 , the image information P 1  of the video camera v 1  is viewed with his left eye, while the image information P 3  of the video camera V 3  is viewed with his right eye. The video camera V 1  and the video camera V 3  are positioned on the left and right sides of the viewfinder  40  as illustrated in  FIG. 6 , therefore, the image information P 1  and the image information P 3  constitute a combination of images having parallax information on the right and left sides. When these image informations are viewed with right and left eyes, the first viewer U 1  can watch 3D images. 
     Example 2 
     Second Viewer U 2   
     An operation when the second viewer U 2  viewing the display device  22  is lying down is described. The viewing posture sensor  23  detects the viewing posture of the second viewer U 2  from the relative posture of the second shutter glasses m 2 . Since the second viewer U 2  is facing the screen with his head tilting through 90 degrees to left (not right) when seen from the side of the display device  22 , the viewing posture sensor  23  determines that the viewing posture of the second viewer U 2  is “tilting to left through 90 degrees” and outputs the determined posture as the viewing posture information S 3  to the control signal output device  24 . 
     The control signal output device  24  generates the control signal S 4  based on the tabulated provisions of  FIG. 9  and outputs the generated control signal S 4  to the second shutter glasses m 2 . While the image information P 2  of the video camera V 2  is being displayed on the display device  22  for the second shutter glasses m 2  worn by the second viewer U 2  “tilting to left through 90 degrees”, the control signal S 4  is outputted so that the penetration unit for left eye is made light-penetrable and the penetration unit for right eye is made light-impenetrable. While the image information P 4  of the video camera V 4  is being displayed on the display device  22 , the control signal S 4  is outputted so that the penetration unit for right eye is made light-penetrable and the penetration unit for left eye is made light-impenetrable. While the image informations P 1  and P 3  of the video cameras V 1  and V 3  are being displayed on the display device  22 , the control signal S 4  is outputted so that the penetration units for right and left eyes are both made light-impenetrable. 
     In the second shutter glasses m 2  worn by the second viewer U 2 , a liquid crystal shutters is controlled based on the control signal S 4 . Therefore, when the second viewer U 2  views the display device  22  through the second shutter glasses m 2 , the image information P 2  of the video camera v 2  is viewed with his left eye, while the image information P 4  of the video camera V 4  is viewed with his right eye. The video camera V 2  and the video camera V 4  are positioned on the upper and lower sides of the viewfinder  40  as illustrated in  FIG. 6 , therefore, the image information P 2  and the image information P 4  constitute a combination of images having parallax information on the upper and lower sides. When these image informations are viewed with right and left eyes, the second viewer U 2  can watch 3D images. When the second viewer U 2  is tilting his head through 90 degrees relative to the display device  22 , the right and left directions for him are almost upper and lower directions in an actual space. 
     So far were described the basic technical characteristics of the conventional 3D image viewing system. The exemplary embodiments of the 3D image viewing system according to the present invention are hereinafter described. 
     Exemplary Embodiment 1 
       FIG. 1  is a block diagram illustrating an overall structure of a 3D image viewing system according to an exemplary embodiment 1 of the present invention. A reference symbol E 1  illustrated in  FIG. 1  is a 3D image playback apparatus. The 3D image playback apparatus E 1  includes an image output device  11  and a transmission device  12 . E 2  is a 3D image display apparatus. The 3D image display apparatus E 2  includes a reception device  21 , a display device  22 , a viewing posture sensor  23 , and a control signal output device  24 .  30  is a transmission cable (HDMI cable). The transmission cable  30  interconnects the transmission device  12  of the 3D image playback apparatus E 1  and the reception device  21  of the 3D image display apparatus E 2 . m 1  is first shutter glasses worn by a first viewer U 1 , and m 2  is second shutter glasses worn by a second viewer U 2 . 
     P 1  is a first image information outputted from the image output device  11 , P 2  is a second image information outputted from the image output device  11 , P 3  is a third image information outputted from the image output device  11 , and P 4  is a fourth image information outputted from the image output device  11 . 
     The image output device  11  of the 3D image playback apparatus E 1  records therein the image informations P 1 -P 4  obtained from a plurality of image pickup positions different to one another by four video cameras V 1 -V 4 . Further, the image output device  11  associates the image informations P 1 -P 4  respectively with information of their image pickup positions and cyclically outputs the resulting informations in the form of video data in a given order. The image informations P 1 -P 4  are the base image data of 3D images. 
     The transmission device  12  transmits respective frames of the image informations P 1 -P 4  (including information of image pickup positions) outputted from the image output device  11  in the form of HDMI (High Definition Multimedia Interface) video data through the HDMI cable  30  which is the only transmission cable. The transmission device  12  outputs the image informations P 1 -P 4  using frame rates four times higher than the image informations P 1 -P 4  while cyclically switching to and from the four informations per frame. Further, the transmission device  12  transmits switching notice packets using HDMI VSI packets. The switching notice packet is transmitted synchronously with the output of the first image information P 1 . 
     The HDMI was defined as a new standard of high definition interfaces used between digital AV devices. The HDMI is an interface specification developed for next-generation digital televisions that enables to transmit uncompressed high-definition video signals and multi-channel digital audio signals with a very high quality as well as control signals through a transmission cable. 
     The HDMI VSI (Vendor Specific Info Frames) packet is a packet used to extend information transmitted through HDMI depending on usage. The switching notice packet is a packet used to identify the information of image pickup positions of frames transmitted as the HDMI video data. 
     In the description of the system, the image informations P 1 -P 4  to be transmitted are not compressed but are transmitted in the form of HDMI video data. However, frame rate thinning, resolution downscaling, interlacing, and progressive conversion may be accordingly performed thereto. 
     The reception device  21  of the 3D image display apparatus E 2  receives the video data and packet data (corresponding to the image informations P 1 -P 4  of a plurality of positions) through the HDMI cable  30  and outputs the received video data in the form of an image signal S 1  to the display device  22 . The reception device  21  outputs, as well as the image signal S 1 , a synchronizing signal S 2  indicating which of the plurality of positions corresponds to the image signal S 1  currently outputted. 
     The HDMI data transmission is performed in three different periods; video data period, data island period, and control period. During the video data period, pixel data of video signals formatted according to the EIA/CEA-861 (video data) is transmitted. During the data island period, packet data of audio stream signals formatted according to the IEC06958 is transmitted. During the control period or data island period, encoded horizontal synchronizing signals and vertical synchronizing signals are transmitted. The packet data transmitted during the data island period includes packet data generated by encoding 4-bit data into 10-bit data according to the TERC4 (TMDS Error Reducing Coding in 4 bit) encoding technique. 
     The display device  22  inputs therein the image signal S 1  outputted from the reception device  21  and displays an image based on the image signals S 1 . The viewing posture sensor  23  detects the postures of the shutter glasses m 1  and m 2  worn by the first and second viewers U 1  and U 2  such as a tilt relative to the display device  22  and generates a display device viewing posture information S 3  (hereinafter, simply called viewing posture information S 3 , and then outputs the generated information to the control signal output device  24 . The posture of the shutter glasses m 1 , m 2  is described below. Conventionally, horizontal and vertical directions of the display device  22  are predefined, and the display device  22  is then placed so that its horizontal direction is in parallel with a floor surface. When the viewer wearing the shutter glasses m 1 , m 2  sits up in a chair and views the display device  22  thus placed, a line which interconnects eye parts of the shutter glasses m 1 , m 2  extends substantially horizontally. At the time, the shutter glasses m 1 , m 2  are taking a posture in parallel with the display device  22 . When the viewer wearing the shutter glasses m 1 , m 2  lies down so that the interconnecting line extends substantially vertically relative to view the display device  22 , the shutter glasses m 1 , m 2  are taking a posture vertical to the display device  22 . Thus, the shutter glasses m 1 , m 2  are positioned through different angles relative to the display device  22  depending on the viewer&#39;s viewing posture, and the differently-angled position is called the posture of the shutter glasses m 1 , m 2 . The posture of the shutter glasses m 1 , m 2  is very important to make the viewer recognize the 3D image. Therefore, it is necessary to select the image information suitable for the posture and control the shutter glasses m 1 , m 2  (control the penetration units for both eyes to be light-penetrable or light-impenetrable) depending on the selected image information. The present exemplary embodiment provides a device configured to detect the postures of the shutter glasses m 1  and m 2  (viewing posture sensor  23 ), thereby making the present invention more available in actual products. 
     The viewing posture sensor  23  generates the viewing posture information S 3  based on the viewer&#39;s position (such as tilt of head) and the viewer&#39;s viewing direction relative to the display device  22  (viewing angle), thereby displaying 3D images flexibly responding to the viewer&#39;s changing viewing angle relative to the display device  22 . The viewing direction is the viewer&#39;s viewing angle relative to the display device  22 , indicating a positional relationship (direction) of the viewer to the display device  22  placed horizontally. 
     The control signal output device  24  receives the viewing posture information S 3  from the viewing posture sensor  23  and the synchronizing signal S 1  from the reception device  21 , and generates and outputs the control signal S 4  for controlling the shutter glasses m 1  and m 2  depending on the received viewing posture information S 3  and synchronizing signal S 2 . 
     In the shutter glasses m 1  and m 2  worn by the first and second viewers U 1  and U 2 , the penetration units for right and left eyes are timing-controlled based on the control signal S 4  to switch to and from the light-penetrable state and the light-impenetrable state. The shutter glasses m 1  and m 2  are each provided with a transmission-reception device (not illustrated in the drawings) for measuring the postures of the viewers U 1  and U 2  relative to the display device  22  through wireless communication with the viewing posture sensor  23 . 
     An operation of the reception device  21  of the 3D image display apparatus E 2  is described referring to a flow chart illustrated in  FIG. 2 . In Step n 1 , the reception device  21  starts to operate and initializes an internal variable i to “1”. In Step n 2 , the reception device  21  determines whether the switching notice packet indicating the output timing of the first image information P 1  is received. When the reception device  21  determines in Step n 2  that the switching notice packet was received, the operation proceeds to Step n 3 . When the reception device  21  determines in Step n 2  that the switching notice packet was not received, the operation proceeds to Step n 4 . The reception device  21  decodes TMDS (Transition Minimized Differential Signaling) transmitted from the transmission device  12  and performs BCH error correction thereto. The reception device  21  also determines whether the VSI packet normally received includes the switching notice packet. The TMDS is encoded according to the TERC4 (TMDS Error Reduction Coding-4). The TMDS is a digital signal transmission method used for data communication with a device such as personal computer, television, and display, and spelled out as transition minimized differential signaling. Step n 2  may simply determine whether the VSI packet normally received includes the switching notice packet, in which case it is preferable that the TERC4 decoding and the BCH error correction of the TMDS transmitted from the transmission device  12  be carried out in a different processing step separately from Step n 2 . 
     In Step n 3  after the reception device  21  determines in Step n 2  that the switching notice packet was received, the internal counter i is initialized to “1”, and the operation proceeds to Step S 4 . In Step n 4  subsequent to Step n 2  or Step n 3 , the reception device  21  determines whether a video frame is received. When the reception device  21  determines in Step n 4  that the video frame was not received, the operation returns to Step n 2 . When the reception device  21  determines in Step n 4  that the video frame was received, the operation proceeds to Step n 5 . The reception device  21  determines whether the video frame is received depending on whether TERC4-encoded or control period-encoded VSYNC (vertical synchronizing signal) is detected. 
     In Step n 5 , the received video frame is outputted as the ith (i is an internal variable) image signal  51 , and outputs the synchronizing signal S 2  indicating that the outputted image signal  51  is the image of the ith video camera. In Step n 6 , the internal variable i is incremented. Then, the operation returns to Step n 2 . 
     An operation of the 3D image viewing system according to the present exemplary embodiment is described. The 3D image playback apparatus E 1  outputs the image informations P 1 -P 4  of a plurality of positions in the form of HDMI video data through the HDMI cable  30  which is the only transmission cable while cyclically switching to and from the four informations per frame. Every time when the first image information P 1  is transmitted, the switching notice packet is transmitted in the data island period. The data island period is a period prior to the transmission of the first image information P 1  during which no video data is outputted. The switching notice packet is transmitted with an enough time for the reception device  21  to complete the data reception during the data island period and perform the error correction before the vertical synchronizing signal VSYNC of the first image information P 1  is outputted in the control period or the data island period. 
     Upon detecting that the video data or the packet data starts to be received through the HDMI cable  30  starts, the reception device  21  of the 3D image display apparatus E 2  starts data reception steps in accordance with the flow chart illustrated in  FIG. 2 . The reception device  21  outputs the received video frame as the image signal S 1  to the display device  22 , thereby cyclically outputting the image informations P 1 -P 4  obtained by the video cameras V 1 -V 4  as the image signal S 1 . Synchronously with the output of the image signal S 1 , the reception device  21  outputs the synchronizing signal S 2  indicating which of the image informations P 1 -P 4  obtained by the first-fourth video cameras V 1 -V 4  corresponds to the image signal S 1  currently outputted to the control signal output device  24 . In the case where the reception device  21  receives the video frame but has received no switching notice packet, it cannot be determined which of the image informations P 1 -P 4  corresponds to the video frame. Therefore, it is unnecessary to output the received video frame as the image signal S 1 . 
     The control signal output device  24  outputs the control signal S 4  by a timing synchronizing with the image signal S 1  outputted to the display device  22  based on the viewing posture information S 3  from the viewing posture sensor  23  and the synchronizing signal S 2  from the reception device  21  for the timing control of the light-penetrable state and the light-impenetrable state in the penetration units for right and left eyes of the shutter glasses m 1  and m 2  worn by the first and second viewers U 1  and U 2 . Accordingly, the first viewer U 1  wearing the first shutter glasses m 1  and the second viewer U 1  wearing the second shutter glasses m 2  can both watch 3D images. The reception device  21  generates the synchronizing signal S 2  in response to the detection of the switching notice packet, and the control signal output device  24  generates the control signal S 4  based on the synchronizing signal S 2 , thereby accurately performing the timing-control of the light-penetrable state and the light-impenetrable state in the shutter glasses m 1  and m 2 . The rest of the operation, which is similar to the basic technical characteristics of the conventional 3D image viewing system illustrated in  FIGS. 6-9 , is not described. 
     In the 3D image viewing system according to the present exemplary embodiment, the 3D image playback apparatus E 1  and the 3D image display apparatus E 2  are interconnected with the HDMI cable  30  which is the only transmission cable. This significantly simplifies and facilitates a wiring arrangement as compared to the system described referring to  FIGS. 6-9 , wherein it is necessary to route different wirings from a plurality of video cameras. 
     The 3D image viewing system is further technically advantageous in that the HDMI-compliant image data can be directly transmitted and received, and the existing HDMI-compliant data island packet can be extended and used to transmit the positional information. To produce the 3D image playback apparatus E 1  and the 3D image display apparatus E 2  for practical use, therefore, any HDMI-compliant transmission devices and reception devices currently available can be directly used with minimum circuit redesign. 
     There are other advantages; only the truly necessary information can be selected from a plurality of image informations and then transmitted, which helps to increase an image display frame rate, and the data to be transmitted through the transmission cable is narrowed down based on the viewing posture information S 3 , which improves a transmission efficiency of the transmission cable. As a result, the video data including a plurality of different image informations can be efficiently transmitted through the only transmission cable. Then, 3D images can be displayed as expected regardless of whether the posture of the viewer wearing the shutter glasses m 1 , m 2  is off balance. 
     The video data stores therein the image informations in a predefined cyclic order, and further includes the switching notice packet indicating that a switching cycle of the plurality of image informations is over. Therefore, the light penetration timing control in the shutter glasses m 1  and m 2  can be very accurate. 
     Exemplary Embodiment 2 
     An exemplary embodiment 2 of the present invention is technically characterized in that any of the plurality of image informations P 1 -P 4  previously determined as unnecessary based on the posture of the viewer U 1 , U 2  relative to the display device  22  is selectively not transmitted from the 3D image playback apparatus E 1  to the 3D image display apparatus E 2 . According to the exemplary embodiment 2, therefore, the viewing posture information S 3  from the viewing posture sensor  23  in the 3D image display apparatus E 2  is transmitted to the 3D image playback apparatus E 1  so that any image information known as unnecessary based on the viewing posture information S 3  received by the 3D image playback apparatus E 1  is excluded from candidates to be selected, and any image information necessary is selectively transmitted. Simply describing a system according to the present exemplary embodiment, it is configured as a view posture sensitive system capable of removing any unnecessary image information not to be displayed. The object of the technical feature is to improve the transmission efficiency of the HDMI cable  30  which is the only transmission cable so that the image display frame rate is improved. 
       FIG. 3  is a block diagram illustrating an overall structure of a 3D image viewing system according to the exemplary embodiment 2. Any reference symbols of  FIG. 3  similar to those illustrated in  FIG. 1  according to the exemplary embodiment 1 denote the same structural elements, therefore, will not be described. 
     A 3D image playback apparatus E 1  according to the present exemplary embodiment is provided with a playback-side transmission-reception device  12   a  in place of the transmission device  12  according to the exemplary embodiment 1. A 3D image display apparatus E 2  according to the present exemplary embodiment is provided with a display-side transmission-reception device  21   a  in place of the reception device  21  according to the exemplary embodiment 1. The playback-side transmission-reception device  12   a  of the 3D image playback apparatus E 1  and the display-side transmission-reception device  21   a  of the 3D image display apparatus E 2  are interconnected with a HDMI cable  30  which is the only transmission cable to enable bidirectional transmission. 
     A viewing posture sensor  23  of the 3D image display apparatus E 2  outputs the generated viewing posture information S 3  to the display-side transmission-reception device  21   a.    
     The display-side transmission-reception device  21   a  of the 3D image display apparatus E 2  is configured to transmit the viewing posture information S 3  inputted from the viewing posture sensor  23  to the playback-side transmission-reception device  12   a  of the 3D image playback apparatus E 1  through the HDMI cable  30  which is the only transmission cable in addition to the features of the reception device  21  according to the exemplary embodiment 1. The display-side transmission-reception device  21   a  outputs the viewing posture information S 3  to the playback-side transmission-reception device  12   a  using HDMI-CEC (Consumer Electronic Control). 
     In addition to the features of the transmission device  12  according to the exemplary embodiment 1, the playback-side transmission-reception device  12   a  of the 3D image playback apparatus E 1 , based on the viewing posture information S 3  received from the 3D image display apparatus E 2 , is configured to:
         select at least one of image informations of respective frames (hereinafter, called frame informations) in the image informations P 1 -P 4  (obtained from different image pickup positions) inputted from the image output device  11 ;   output the selected frame information per frame as the HDMI video data; and   transmit the switching notice packet using the VSI packet synchronously with the output timing of the video data.       

     More specifically, the playback-side transmission-reception device  12   a  is configured to:
         select from the image informations P 1 -P 4  obtained from a plurality of positions an image signal for right eye and an image signal for left eye for the first shutter glasses m 1  worn by the first viewer U 1  based on the viewing posture information S 3 ;   output the selected image signals for right and left eyes as the first and second image informations (HDMI video data);   select from the image informations P 1 -P 4  obtained from a plurality of positions an image signal for right eye and an image signal for left eye for the second shutter glasses m 2  worn by the second viewer U 2  based on the viewing posture information S 3 ; and   output the selected image signals for right and left eyes as the third and fourth image informations (HDMI video data).       

     The image information is thus selected based on the viewing posture information S 3  so as to display 3D images most suitable for the viewing postures of the viewers U 1  and U 2  who are watching the display device  22 . A timing by which the playback-side transmission-reception device  12   a  transmits the switching notice packet is equal to a timing of outputting the first image information. 
       FIG. 4  is a correlative table of the viewing posture information S 3  and the image informations P 1 -P 4  of a plurality of positions, illustrating how the control signal S 4  inputted to the shutter glasses m 1  and m 2  is defined. 
       FIG. 5  is a correlative table of the viewing posture information S 3  indicating the viewing postures of the viewers U 1  and U 2  and the image informations to be suitably selected for the respective postures in the playback-side transmission-reception device  12   a . The rest of the technical characteristics are similar to exemplary embodiment, therefore, will not be described. 
     An operation of the 3D image viewing system according to the present exemplary embodiment is described. The operation described below is performed in the case where, for example, the first viewer U 1  is watching the display device  22  with a tilt to right through 90 degrees relative to the display device  22 , and the second viewer U 2  is watching the display device  22  with a tilt to left through 90 degrees relative to the display device  22 . It is to be noted that the directions of the respective tilts, right and left, describe the tilts of the viewers U 1  and U 2  when seen from the side of the display device  22 . When the description says that the first viewer U 1  is tilting to right through 90 degrees relative to the display device  22 , the first viewer U 1  is tilting to left on the drawing of  FIG. 7 . When the description says that the second viewer U 2  is tilting to left through 90 degrees relative to the display device  22 , the second viewer U 2  is tilting to right on the drawing of  FIG. 7 . Thus, the directions of the respective tilts of the viewers U 1  and U 2  are opposite to the positional relationship drawn in  FIG. 7 . 
     The first shutter glasses m 1  worn by the first viewer U 1  tilting to right through 90 degrees relative to the display device  22  needs; the image information P 4  taken by the fourth video camera V 4  in its penetration unit for left eye, and the image information P 2  taken by the second video camera V 2  in its penetration unit for right eye. 
     The second shutter glasses m 2  worn by the second viewer U 2  tilting to left through 90 degrees relative to the display device  22  needs; the image information P 2  taken by the second video camera V 2  in its penetration unit for left eye, and the image information P 4  taken by the fourth video camera V 4  in its penetration unit for right eye. 
     This means that neither of the first glasses m 1  nor the second shutter glasses m 2  needs the display of the image information P 3  taken by the third video camera V 3  or the image information P 4  taken by the fourth video camera V 4 . Therefore, when the viewing posture information S 3  is transmitted from the viewing posture sensor  23  of the 3D image display apparatus E 2  to the display-side transmission-reception device  21   a , and the viewing posture information S 3  is inputted to the playback-side transmission-reception device  12   a  of the 3D image playback apparatus E 1  through the HDMI cable  30 , the playback-side transmission-reception device  12   a  selects the second image information P 2  and the fourth image information P 4  determined as necessary based on the viewing posture information S 3  from all of the four image informations P 1 -P 4  inputted from the image output device  11 , and rules out the first image information P 1  and the third image information P 3  determined as unnecessary based on the viewing posture information S 3  from the candidates to be selected. Below is given a more detailed description. 
     The viewing postures of the first and second viewers U 1  and U 2  are detected by the viewing posture sensor  23  in the 3D image display apparatus E 2 , and the viewing posture information S 3  is outputted to the display-side transmission-reception device  21   a . Further, the viewing posture information S 3  is transmitted to the playback-side transmission-reception device  12   a  of the 3D image playback apparatus E 1  through the HDMI cable  30  which is the only communication cable. 
     As described earlier, the first viewer U 1  is taking the viewing posture tilting to right through 90 degrees relative to the display device  22 . It is known from the table illustrated in  FIG. 4  that, in the case of the posture tilting to right through 90 degrees, the image information P 4  taken by the fourth video camera V 4  should be inputted as an image signal for left eye, and the image information P 2  taken by the second video camera V 2  should be inputted as an image signal for right eye. The second viewer U 2  is taking the viewing posture tilting to left through 90 degrees relative to the display device  22 . It is known from the table illustrated in  FIG. 4  that, in the case of the posture tilting to left through 90 degrees, the image information P 2  taken by the second video camera V 2  should be inputted as an image signal for left eye, and the image information P 4  taken by the fourth video camera V 4  should be inputted as an image signal for right eye. According to the table, the image information P 1  taken by the first video camera V 1  is not transmitted whenever the viewing posture is tilted through 90 degrees regardless of the direction, right or left, and the image information P 3  taken by the third video camera V 3  is not transmitted whenever the viewing posture is tilted through 90 degrees regardless of the direction, right or left. 
     Therefore, the playback-side transmission-reception device  12   a  of the 3D image playback apparatus E 1  which received the viewing posture information S 3  selects the fourth image information P 4  as the image signal for left eye for the first shutter glasses m 1  worn by the first viewer U 1 , while selecting the second image information P 2  as the image signal for right eye for the first shutter glasses m 1 . Further, the transmission-reception device  12   a  selects the second image information P 2  as the image signal for left eye for the second shutter glasses m 2  worn by the second viewer U 2 , while selecting the fourth image information P 4  as the image signal for right eye for the second shutter glasses m 2 . The image informations P 4 , P 2 , P 2  and P 4  are, in the mentioned order, the first image information, second image information, third image information, and fourth image information. The transmission-reception device  12   a  then transmits these image informations P 4 , P 2 , P 2  and P 4  as the HDMI video data repeatedly to the transmission-reception device  21   a  of the 3D image display apparatus E 2  through the HDMI cable  30 . In the data transmission described above, the image information P 1  taken by the first video camera V 1  and the image information P 3  taken by the third video camera V are not transmitted from the play-back transmission-reception device  12   a.    
     The switching notice packet is transmitted during the data island period which is a video data non-output period prior to the output of the first image information, which is the image signal for left eye of the first shutter glasses m 1 , as the video data. When the switching notice packet is transmitted, packet transmission intervals should be set so that the display-side transmission-reception device  21   a  can complete the data reception during the data island period and the display device is thereby given an enough time for the error correction before the output of the vertical synchronizing signal VSYNC of the image signal for left eye of the first shutter glasses m 1  during the control period or the data island period. 
     Upon detecting the start of the video data or packet data reception through the HDMI cable  30 , the display-side transmission-reception device  21   a  of the 3D image display apparatus E 2  starts to perform data reception steps as illustrated in the flow chart of  FIG. 2 . The display-side transmission-reception device  21   a  outputs the received video data in the form of the image signal S 1 , and further outputs the synchronizing signal S 2  synchronously with the output of the image signal S 1 . The synchronizing signal S 2  is a signal indicating which of the first-fourth image informations corresponds to the image signal S 1  currently outputted. In the case where the display-side transmission-reception device  21   a  receives the video frame but has received no switching notice packet, it cannot be determined which of the image informations P 1 -P 4  corresponds to the video frame. Therefore, it is unnecessary to output the received video frame as the image signal S 1 . 
     As illustrated in  FIG. 5 , while the first image information (image signal for left eye of the first shutter glasses m 1  worn by the first viewer U 1 ) is being displayed on the display device  22 , the control signal output device  24  makes:
         the penetration unit for left eye of the first shutter glasses m 1  light-penetrable; and   any penetration units but the penetration unit for left eye of the first shutter glasses m 1  (penetration unit for right eye of the first shutter glasses m 1 , and penetration units for right and left eyes of the second shutter glasses m 2 ) light-impenetrable.       

     While the second image information (image signal for right eye of the first shutter glasses m 1 ) is being displayed on the display device  22 , the control signal output device  24  makes:
         the penetration unit for right eye of the first shutter glasses m 1  light-penetrable; and   any penetration units but the penetration unit for right eye of the first shutter glasses m 1  (penetration unit for left eye of the first shutter glasses m 1 , and penetration units for right and left eyes of the second shutter glasses m 2 ) light-impenetrable.       

     While the third image information (image signal for left eye of the second shutter glasses m 2  worn by the second viewer U 2 ) is being displayed on the display device  22 , the control signal output device  24  makes:
         the penetration unit for left eye of the second shutter glasses m 2  light-penetrable; and   any penetration units but the penetration unit for left eye of the second shutter glasses m 2  (penetration unit for right eye of the second shutter glasses m 2 , and penetration units for right and left eyes of the first shutter glasses m 1 ) light-impenetrable.       

     While the fourth image information (image signal for right eye of the second shutter glasses m 2  worn by the second viewer U 2 ) is being displayed on the display device  22 , the control signal output device  24  makes:
         the penetration unit for right eye of the second shutter glasses m 2  light-penetrable; and   any penetration units but the penetration unit for right eye of the second shutter glasses m 2  (penetration unit for left eye of the second shutter glasses m 2 , and penetration units for right and left eyes of the first shutter glasses m 1 ) light-impenetrable.       

     As a result of these processing steps, the image informations selected by the playback-side transmission-reception device  12   a  for a plurality of viewers can be correctly visually recognized as 3D images by the first and second viewers U 1  and U 2  properly wearing the shutter glasses m 1  and m 2 . 
     The present exemplary embodiment can improve the transmission efficiency of the HDMI cable  30  which is the only transmission cable, thereby increasing the image display frame rate. 
     In the description of the present exemplary embodiment, there are two viewers. In the case where there is a third viewer in addition to the two viewers, the playback-side transmission-reception device  12   a  transmits fifth and sixth image informations, and the control signal output device  24  makes penetration units for right and left eye of shutter glasses worn by the third viewer light-penetrable while the fifth and sixth image information are being displayed. In the case of at least four viewers, the image information to be inputted are increased likewise for shutter glasses worn by more viewers. 
     The exemplary embodiments 1 and 2 both described the image viewing system wherein the images taken by four video cameras are used, however, the present invention does not necessarily limit the number or location of video cameras. Further, the image viewing system according to the present invention is applicable to images of computer graphics based on 3D data as well as the images taken by video cameras. In such a case, for example, the video cameras are replaced with home video game machines capable of rendering images of computer graphics through a plurality of angles at the same time based on 3D model. 
     According to the exemplary embodiments 1 and 2, the first and second viewers U 1  and U 2  who are watching the display unit  22  are seated substantially in front of the display device  22 . A plurality of image pickup units each including a plurality of video cameras may be provided at a plurality of different positions relative to a photographic subject so that 3D images can be displayed at any positions regardless of how the viewer&#39;s position relative to the display unit  22  changes. The suggested structure is suitable for such a structural characteristic as disclosed in the Patent Document 1 wherein a viewer can watch 3D images regardless of his positional relationship with a display device horizontally placed (regular position, position opposite to the regular position, or positions on lateral sides of the regular position). 
     In the case of such a system, the control signal output device  24  is preferably configured to output the control signal depending on the viewer&#39;s viewing angle relative to the display device  22  other than the tilt of his head, so that the system can flexibly respond to any change of the viewer&#39;s viewing angle relative to the display device. The playback-side transmission-reception device  12   a  is preferably configured not to transmit any images viewable by none of the viewers because their shutter glasses are both light-impenetrable due to the control signal S 4  outputted from the control signal output device  24  to the 3D image display apparatus E 2  in accordance with the viewing posture information S 3  from the viewing posture sensor  23 . Accordingly, 3D images can be simultaneously viewed at a large number of viewing positions. 
     As described so far, the present exemplary embodiment can selectively transmit only the necessary image information among a plurality of image informations based on the viewing posture information S 3 , thereby increasing the image display frame rate. Further, the present exemplary embodiment narrows down the data to be transmitted through the transmission cable, thereby improving the transmission efficiency of the transmission cable. As a result, the video data including a plurality of different image informations can be efficiently transmitted through only one transmission cable. As well as these advantages, the present exemplary embodiment naturally enables 3D display as expected regardless of any tilt of the viewer wearing the shutter glasses m 1 , m 2 . 
     INDUSTRIAL APPLICABILITY 
     The present invention provides an advantageous technology for 3D image viewing in, for example, home theaters, and 3D image display apparatuses, 3D image playback apparatuses, and 3D image viewing system applicable to home-use game machines in which computer graphics is used. 
     When the data island packet is extended and used to transmit the information of image pickup positions, any HDMI-compliant transmission devices and reception devices currently available can be directly used with minimum circuit redesign to obtain the 3D image playback apparatus. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
         C 1 -C 4  transmission cable 
         E 1  3D image playback apparatus 
         E 2  3D image display apparatus 
         E 3  image selector apparatus 
         m 1  first shutter glasses (liquid crystal glasses) 
         m 2  second shutter glasses (liquid crystal glasses) 
         n 1 -n 6  processing steps by reception device 
         P 1 -P 4  first-fourth image informations 
         S 1  image signal 
         S 2  synchronizing signal 
         S 3  viewing posture information 
         S 4  control signal 
         U 1  first viewer 
         U 2  second viewer 
         V 1 -V 4  first-fourth video cameras 
           11  image output device 
           12  transmission device 
           12   a  playback-side transmission-reception device 
           21  reception device 
           21   a  display-side transmission-reception device 
           22  display device 
           23  viewing posture sensor 
           24  control signal output device 
           30  HDMI cable 
           40  viewfinder of image pickup device 
           50  photographic subject