Abstract:
A transmission apparatus for digitally transmitting a video signal through a transmission path, includes an acquiring unit to acquire a video signal generated by decoding a compressively coded signal, and a transmission pass coder to multiplex a luminous signal and a color difference signal which compose the acquired video signal in a video signal period, and multiplex a control signal related to the video signal in a blanking period. The control signal is (1) information to be used by a receiving apparatus which receives the video signal to adjust image quality of the video signal, and (2) includes information indicating whether the compressively coded signal based on which the video signal transmitted by the transmission pass coder is generated is I picture, P picture, or B picture.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. Ser. No. 12/109,636, filed Apr. 25, 2008, which is a continuation of U.S. Ser. No. 10/088,468, filed Jun. 11, 2002 and patented as U.S. Pat. No. 7,394,854, which is a national stage application of PCT/JP01/06340, filed Jul. 23, 2001, which claims priority to JP 2000-220751, filed Jul. 21, 2000. Each of the above-identified applications are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a signal transmission system for transmitting picture signals and, more particularly, to a signal transmission system in which hardware configurations of the video signal transmitting end and receiving end can be simplified. 
       BACKGROUND OF THE INVENTION 
       [0003]    A prior art example will be described with reference to  FIG. 17 .  FIG. 17  is a block diagram illustrating the configuration of a conventional signal transmission system. 
         [0004]    In  FIG. 17 , reference numeral  1701  denotes a video signal output unit (transmitting end) such as a STB (Set-top box), which outputs a video signal. Numeral  1702  denotes an MPEG decoder, which receives digital broadcasting and outputs baseband Y color-difference signals. Numeral  1703  denotes a signal conversion circuit, which converts the Y color-difference signals into RGB signals. Numeral  1704  denotes a transmission path encoding circuit, which encodes the signals converted by the signal conversion circuit  1703  into signals in formats suited to the transmission path. Numeral  1705  denotes a display unit (receiving end) such as a TV monitor. Numeral  1706  denotes a transmission path decoding circuit, which decodes the signals encoded by the transmission path encoding circuit  1704 . Numeral  1707  denotes a signal conversion circuit, which converts the RGB signals outputted from the transmission path decoding circuit  1706  into YPBPR signals. Numeral  1708  denotes a Y processing circuit, which processes luminance signals Y out of the output from the signal conversion circuit  1707 . Numeral  1709  denotes a chrominance processing circuit, which processes chrominance signals out of the output from the signal conversion circuit  1707 . Numeral  1710  denotes a signal conversion circuit, which receives the outputs from the Y processing circuit  1708  and the chrominance processing circuit  1709  and converts the Y color-difference signals into the RGB signals. Numeral  1711  denotes a display device, which receives the output from the signal conversion circuit  1710  and outputs it to a LCD or CRT. 
         [0005]    An operation of the so-configured signal transmission system will be described. 
         [0006]    The MPEG decoder  1702  receives digital broadcasting and outputs baseband video signals. As the data format of the MPEG is based on Y color-difference signals, the output here is YPBPR, or YUV, or YCbCr. Further, this signal must be converted into RGB signals to encode it adaptively to a transmission path, and thus the Y color-difference signals are converted into RGB signals by the signal conversion circuit  1703 . The converted RGB signals are encoded into signal forms suited to the transmission path by the transmission path encoding circuit  1704 . 
         [0007]    On the other hand, on the TV monitor  1705  side, the transmission path decoding circuit  1706  receives the signals encoded by the transmission path encoding circuit  1704  and generates the original RGB signals. The RGB signals are converted into the YPBPR of the Y color-difference signals by the signal conversion circuit  1707 . Here, to perform independent processing on the TV monitor  1705  side, the Y signals are processed by the Y processing circuit  1708 , and the chrominance signals PBPR are enhanced by the chrominance processing circuit  1709 , respectively, and these signals are outputted. The enhanced and outputted Y color-difference signals are converted into the RGB signals by the signal conversion circuit  1710  so as to be outputted to the final display device  1711 . The display device  1711  outputs the RGB signals which have been outputted from the signal conversion circuit  1710 , thereby to perform display. 
         [0008]    However, in the above-described conventional signal transmission system, since the transmission path encoding is performed on the RGB signals, the output from the MPEG decoder is once converted into the RGB signals, encoded, and transmitted through the transmission path and, thereafter, the RGB signals must be converted into the YPBPR to perform signal processing again on the monitor side and, further, the Y color-difference signals must be converted into the RGB signals once again to output the RGB signals to the final display device, resulting in a drawback of requiring a lot of hardware. 
         [0009]    The present invention is made to solve the above-mentioned problems and has for its object to provide a signal transmission system in which hardware configurations of the video signal transmitting end and receiving end can be simplified. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one embodiment of the present invention, there is provided a signal transmission system for transmitting a video signal, comprising: a signal transmission unit including; a decoder which receives digital broadcasting and outputs a luminance signal and two color difference signals, and an encoding circuit which encodes the luminance signal and the respective color difference signals into signal forms suited to a transmission path, and transmits the encoded signals; and a signal reception unit including; a decoding circuit which receives the encoded luminance signal and respective color difference signals, and decodes these signals, a luminance signal processing circuit which processes the decoded luminance signal, a color difference signal processing circuit which processes the respective decoded color difference signals, and a signal conversion circuit which converts the luminance signal outputted from the luminance signal processing circuit and the respective color difference signals outputted from the color difference signal processing circuit into RGB signals. 
         [0011]    Therefore, it is possible to realize a signal transmission system in which hardware configurations at the video signal transmitting end and receiving end can be simplified. 
         [0012]    According to a second embodiment of the present invention, there is provided a signal transmission system for transmitting a video signal through a transmission path, comprising: a signal transmission unit including; a decoder which receives digital broadcasting and outputs a luminance signal and two color difference signals, a time division multiplexing circuit which sub-samples the two color difference signals to signals with half pixel rates, subjects the signals to time division multiplexing, and outputs a multiplexed signal, and an encoding circuit which encodes the luminance signal and the multiplexed signal into signal forms suited to a transmission path, and transmits the encoded signals; and a signal reception unit including; a decoding circuit which receives the encoded luminance signal and multiplexed signal, and decodes these signals, a demultiplexing circuit which demultiplexes the decoded multiplexed signal into the original two color difference signals, a luminance signal processing circuit which processes the decoded luminance signal, a color difference signal processing circuit which processes the respective color difference signals demultiplexed, and a signal conversion circuit which converts the luminance signal outputted from the luminance signal processing circuit and the respective color difference signals outputted from the color difference signal processing circuit into RGB signals. 
         [0013]    Since two color difference signals are multiplexed and transmitted, only two transmission paths are required while three transmission paths are required in the conventional system, resulting in a signal transmission system in which hardware configurations at the video signal transmitting end and receiving end can be simplified. 
         [0014]    According to a third embodiment of the present invention, there is provided a signal transmission system for transmitting a video signal and an audio signal, comprising: a signal transmission unit including; an MPEG decoder which receives digital broadcasting and outputs the video/audio signal, an output interface which outputs the video/sound signal that has been outputted from the MPEG decoder, an I2C controller which outputs an I2C (Inter IC control) signal, a CPU which controls the whole unit, and a program ROM which stores an operation program of the CPU; and a signal reception unit including; an input interface which receives the video/audio signal from the signal transmission unit, a device interface which converts the video/audio signal into a video image and a sound, a video/audio output device which outputs the video image and the sound outputted from the device interface, to the outside, and an I2C controller which has a ROM table in which information relating to performance of the signal reception unit is stored, receives an I2C signal from the signal transmission unit, and outputs the information stored in the ROM table to the signal transmission unit according to a request from the signal transmission unit. 
         [0015]    Therefore, the signal transmission unit can be previously informed of the performance of the signal reception unit, and signal transmission can be performed on the basis of the performance of the signal reception unit without transmitting a signal at a rate which cannot be scanned on the signal reception unit side as in the conventional system, thereby avoiding such a problem that no video image is displayed or no sound is outputted at the signal reception side. 
         [0016]    According to a fourth embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the ROM table stores information relating to resolution of a video image that can be outputted from the video/audio output device. 
         [0017]    Therefore, the signal transmission unit can be previously informed of the resolution of a video image that can be outputted from the signal reception unit, thereby realizing a signal transmission system which can avoid such a problem that no video image is displayed. 
         [0018]    According to a fifth embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the ROM table stores information relating to the number of channels of audio that can be outputted from the video/audio output device. 
         [0019]    Therefore, the signal transmission unit can be previously informed of the number of channels of audio that can be outputted from the signal reception unit, thereby realizing a signal transmission system which can avoid such a problem that no sound is outputted. 
         [0020]    According to a sixth embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the ROM table stores information relating to a signal conversion method for converting the luminance signal and color difference signals into RGB signals. 
         [0021]    Therefore, the signal transmission unit can be previously informed of a signal conversion method to be performed at the signal reception unit side, thereby realizing a signal transmission system which can perform signal conversion correctly. 
         [0022]    According to a seventh embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the ROM table stores information relating to gamma control of the video signal. 
         [0023]    Therefore, the signal transmission unit can be previously informed of gamma control of a video signal at the signal receiving end, whereby the transmission unit can output a non-enhanced video signal to the signal reception unit. 
         [0024]    According to an eighth of the present invention, in the signal transmission system as defined in embodiment 3, the ROM table stores information relating to whether or not the signal reception unit has a mode in which a video image is not subjected to enhancement processing. 
         [0025]    Therefore, when the signal reception unit has a mode in which no enhancement processing is performed, the signal transmission unit can forcibly switch the reception unit to that mode, whereby the signal reception unit can display a video image which is not enhanced in color. 
         [0026]    According to a ninth embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the ROM table stores information relating to a maker code and a device code of the signal reception unit. 
         [0027]    Therefore, the signal transmission unit can be previously informed of the maker code and device code of the signal reception unit, and when up-conversion of a picture is carried out, the respective performances of the signal transmission unit and the signal reception unit are compared, and either of these units having better performance can be automatically selected. 
         [0028]    According to a tenth embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the signal reception unit outputs the kind of aspect conversion processing that is currently performed to output a video image, to the signal transmission unit through the I2C controller. 
         [0029]    Therefore, the signal transmission unit can transmit a video signal so that the signal reception unit can obtain a correct aspect. 
         [0030]    According to an eleventh embodiment of the present invention, in the signal transmission system as defined in embodiment 3, the signal transmission unit includes a selector which multiplexes control information in a vertical retrace period of the video signal and outputs it, said control information indicating whether a video frame signal, that is currently outputted from the MPEG decoder separately from the video/audio signal, is generated by being repeatedly outputted in the MPEG decoder or not; and the signal reception unit includes a control information separation unit which separates the control information from the video signal, and a picture quality control unit which subjects the video signal to an adaptive signal processing according to the control information, and outputs the video signal to the device interface. 
         [0031]    Therefore, the signal reception unit can be operated on the basis of the control information comprising minimum requirements such as brightness, contrast, volume, and the like. 
         [0032]    According to a twelfth embodiment of the present invention, in the signal transmission system as defined in embodiment 11, the control information is information indicating a picture encoding method based on the MPEG standard, by which I, P, and B pictures can be discriminated from each other. 
         [0033]    Therefore, it is possible to realize a signal transmission system which can set parameters for noise removal for every frame. 
         [0034]    According to a thirteenth embodiment of the present invention, in the signal transmission system as defined in embodiment 11, the control information is compression ratio information based on the MPEG standard. 
         [0035]    Therefore, it is possible to realize a signal transmission system which can set parameters for noise removal for every frame. 
         [0036]    According to a fourteenth embodiment of the present invention, in the signal transmission system as defined in embodiment 11, the control information is information indicating whether a material before being MPEG-encoded is picked up by progressive scanning or interlaced scanning. 
         [0037]    Therefore, the signal reception unit can select a method of conversion from interlacing to progressive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  is a block diagram illustrating the configuration of a signal transmission system according to a first embodiment. 
           [0039]      FIG. 2  is a block diagram illustrating the configuration of a signal transmission system according to a second embodiment. 
           [0040]      FIG. 3  is a schematic block diagram of a signal transmission system according to a third embodiment. 
           [0041]      FIG. 4  is a block diagram illustrating a detailed configuration of the signal transmission system according to the third embodiment. 
           [0042]      FIG. 5  is a diagram for explaining an initial protocol in the signal transmission system according to the third embodiment. 
           [0043]      FIG. 6  is a diagram illustrating a state of screen display of a 16:9 wide material TV. 
           [0044]      FIG. 7  is a diagram showing an example of a ROM table. 
           [0045]      FIG. 8  is a diagram for explaining a retrace period in a case where an output video rate is interlacing and in a case where the output video rate is progressive, respectively. 
           [0046]      FIG. 9  is a flowchart for explaining an operation of a signal transmission system according to a fourth embodiment of the present invention. 
           [0047]      FIG. 10  is a diagram for explaining an operation of a selector. 
           [0048]      FIG. 11  is a diagram showing an example of the constitution of control data. 
           [0049]      FIG. 12  is a diagram illustrating the composition of a selector in the signal transmission system according to the fourth embodiment. 
           [0050]      FIG. 13  is a block diagram illustrating the configuration of the receiving end of the signal transmission system according to the fourth embodiment. 
           [0051]      FIG. 14  is a diagram showing an example of a control signal transmitted for each frame in the signal transmission system according to the fourth embodiment. 
           [0052]      FIG. 15  is a conventional block diagram illustrating a conversion circuit when converting a telecine material from 24p into for example 60p. 
           [0053]      FIG. 16  is a diagram illustrating a field repeat signal transmission system in the fourth embodiment. 
           [0054]      FIG. 17  is a block diagram illustrating the configuration of a conventional signal transmission system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described here are merely examples and the present invention is not restricted to these embodiments. 
       Embodiment 1 
       [0056]    Hereinafter, a signal transmission system according to a first embodiment of the present invention will be described with reference to  FIG. 1 . 
         [0057]      FIG. 1  is a block diagram illustrating the configuration of the signal transmission system according to the first embodiment of the present invention. 
         [0058]    In  FIG. 1 , numeral  101  denotes a video signal output unit such as a STB, which outputs a video signal. Numeral  102  denotes an MPEG decoder, which receives digital broadcasting or the like and outputs a luminance signal and two color-difference signals. Numeral  103  denotes a transmission path encoding circuit, which encodes the luminance signal and the color-difference signals outputted from the MPEG decoder  102  into signals in the forms suited to a transmission path, and transmits these signals. Numeral  104  denotes a display unit such as a TV monitor, which displays the video signal. Numeral  105  denotes a transmission path decoding circuit, which receives the luminance signal and the color difference signals encoded by the transmission path encoding circuit  103 , and decodes these signals. Numeral  106  denotes a Y processing circuit, which processes the decoded luminance signal that has been outputted from the transmission path decoding circuit  105 . Numeral  107  denotes a chrominance processing circuit, which processes chrominance signals out of the signals outputted from the transmission path decoding circuit  105 . Numeral  108  denotes a signal conversion circuit, which converts the Y color-difference signals that have been outputted from the Y processing circuit  106  and the chrominance processing circuit  107  into RGB signals. Numeral  109  denotes a display device, which receives the output from the signal conversion circuit  108  and displays it. 
         [0059]    The operation of the so-configured signal transmission system will be described. 
         [0060]    The MPEG decoder  102  receives a broadcast wave of digital broadcasting and outputs baseband YPBPR signals in conformity with the MPEG standard. Since, in the conventional signal transmission system, not the Y color-difference signals but the RGB signals are encoded and transmitted, the YPBPR signals outputted from the MPEG decoder are converted into the RGB signals. In the signal transmission system according to the first embodiment, however, the YPBPR signals are inputted, as they are, to the transmission path encoding circuit  103  which performs encoding suited to the transmission path. The transmission path encoding circuit  103  encodes the inputted YPBPR signals into signals in the forms suited to the transmission path and outputs the encoded signals to the transmission path. 
         [0061]    The transmission path decoding circuit  105  decodes the encoded signals which have been received through the transmission path, into the original YPBPR signals, and outputs the decoded YPBPR signals. Among the outputs from the transmission path decoding circuit  105 , the Y signal as the luminance signal is inputted to the Y processing circuit  106  and subjected to various signal processings such as adjustment of luminance contrast. Further, among the outputs from the transmission path decoding circuit  105 , the chrominance signals of PB and PR are subjected to required processings by the chrominance processing circuit  107 , respectively. The signal conversion circuit  108  converts the processed Y signal and chrominance signals which are outputted from the Y processing circuit  106  and the chrominance processing circuit  107  into the RGB signals, and outputs them to the display device  109 . The display device  109  receives the RGB signals outputted from the signal conversion circuit  108  and displays them. 
         [0062]    In this signal transmission system according to the first embodiment, the Y color-difference signals outputted from the MPEG decoder  102  are encoded and transmitted as they are, whereby a circuit for converting the Y color-difference signals into the RGB signals can be dispensed with at the video signal output unit  101  side (transmitting end). Further, at the display unit  104  side (receiving end), the Y color-difference signals are inputted as they are, whereby a circuit for converting the RGB signals into the Y color-difference signals can be dispensed with, resulting in simplified hardware configuration. 
       Embodiment 2 
       [0063]    Hereinafter, a signal transmission system according to a second embodiment of the present invention will be described with reference to  FIG. 2 . 
         [0064]      FIG. 2  is a block diagram illustrating the configuration of the signal transmission system according to the second embodiment of the present invention. 
         [0065]    In  FIG. 2 , numeral  201  denotes a video signal output unit such as a STB, which outputs a video signal. Numeral  202  denotes an MPEG decoder, which receives digital broadcasting or the like and outputs a luminance signal and two color-difference signals. Numeral  203  denotes a time division multiplexing circuit, which time-division-multiplexes color difference signals PB and PR that have been outputted from the MPEG decoder  202  and converts them into a single signal line. Numeral  204  denotes a transmission path encoding circuit, which encodes the Y signal outputted from the MPEG decoder  202  and the multiplexed PBPR signal outputted from the time division multiplexing circuit  203  into signals in the forms suited to the transmission path, and transmits these signals. Numeral  205  denotes a display unit such as a TV monitor, which displays the video signal. Numeral  206  denotes a transmission path decoding circuit, which decodes the signals that have been encoded so as to suit the transmission path, into the original Y signal and multiplexed PBPR signal, and outputs these signals. Numeral  207  denotes a demultiplexing circuit, which demultiplexes the multiplexed PBPR signal into the original PB signal and PR signal. Numeral  208  denotes a Y processing circuit, which processes the Y signal outputted from the transmission path decoding circuit  206 . Numeral  209  denotes a chrominance processing circuit, which processes the demultiplexed PB signal and PR signal. Numeral  210  denotes a signal conversion circuit, which converts the inputted YPBPR signals into RGB signals. Numeral  211  denotes a display device, which displays the RGB signals outputted from the signal conversion circuit  210 . 
         [0066]    The operation of the so-configured signal transmission system will be described. 
         [0067]    The MPEG decoder  202  receives a video signal, and decodes it to output three signal lines of YPBPR, i.e., a baseband Y signal and two color difference signals, to the time division multiplexing circuit  203 . As the sampling frequency of the PB signal and the PR signal in the horizontal direction is one half of that of the Y signal, the time division multiplexing circuit  203  performs time-base multiplexing on the PB signal and the PR signal, arranges them alternately, and outputs them in a single line. The transmission path encoding circuit  204  subjects the multiplexed signal PBPR and the Y signal outputted from the MPEG decoder  202  to encoding that is suited to the transmission path, and outputs them to the display unit  205  side. 
         [0068]    The transmission path decoding circuit  206  decodes the signals received through the transmission path into the original luminance signal Y and multiplexed signal PBPR and outputs them to the demultiplexing circuit  207 . Since the PBPR signal is time-base multiplexed, the demultiplexing circuit  207  returns the PBPR signal into the original PB signal and PR signal. Then, the Y processing circuit  208  performs predetermined processing on the luminance signal Y, and the chrominance processing circuit  209  performs predetermined processing on the signals PB and PR. The YPBPR signals obtained in this way are converted into the RGB signals by the signal conversion circuit  210 , and the RGB signals are inputted to the display device  211  and displayed. 
         [0069]    Since thee signal transmission system according to the second embodiment is provided with the time division multiplexing circuit  203  which multiplexes the two chrominance signals and outputs them in a single signal line, only two transmission paths are required in this second embodiment while three transmission paths are required in the first embodiment. 
       Embodiment 3 
       [0070]    Hereinafter, a signal transmission system according to a third embodiment of the present invention will be described with reference to  FIGS. 3 to 7 . 
         [0071]      FIG. 3  is a block diagram schematically illustrating the configuration of the signal transmission system according to the third embodiment of the present invention. 
         [0072]    In  FIG. 3 , numeral  301  denotes a STB for receiving digital broadcasting or the like, which outputs a video signal. Numeral  302  denotes a TV monitor which displays the video signal received from the STB  301 . It is assumed that I2C bidirectional communication is possible between the STB  301  and the TV monitor  302 . 
         [0073]      FIG. 4  is a block diagram for explaining the STB  301  and the TV monitor  302  in detail. In  FIG. 4 , the same or corresponding constituent elements as those shown in  FIG. 3  are denoted by the same reference numerals, and their descriptions will be omitted. 
         [0074]    In  FIG. 4 , numeral  402  denotes an MPEG decoder, which receives digital broadcasting or the like and outputs a baseband signal of a video image. Numeral  403  denotes a video output interface, which outputs the video signal that has been outputted from the MPEG decoder  402 . Numeral  404  denotes a CPU, which is operated by a program ROM  405  and controls the MPEG decoder  402  and its periphery. Further, the CPU  404  can also control an I2C controller  406 . Numeral  408  denotes a video input interface, to which the video signal received through a transmission path is inputted. Numeral  409  denotes a device interface, which converts the video signal into a signal suitable for a display device for displaying. Numeral  410  denotes a display device itself such as a LCD or a CRT. Numeral  411  denotes an I2C controller, which controls an I2C bus and has a ROM table  412  in which information relating to performance of the TV monitor  302  is stored. Further, the ROM table  412  includes information relating to resolution of a video image that can be outputted from the display device  410 , information relating to the number of channels of audio that can be outputted from the display device  410 , information relating to a signal conversion method for converting a luminance signal and color difference signals into RGB signals, information relating to gamma control of the video signal, information as to whether or not the TV monitor  302  has a mode in which the video image is not subjected to enhancement processing, and information relating to a maker code and a device code of the TV monitor  302 . Further, the TV monitor  302  outputs the kind of aspect conversion processing which is presently performed to output the video image, to the STB  301  through the I2C controller  411 . 
         [0075]    The operation of the so-configured signal transmission system will be described with reference to  FIG. 5 . Here, an initial protocol by the I2C will be described with reference to  FIG. 5 . 
         [0076]    First of all, the STB  301  side asks the TV monitor  302  about the maker code and device code of the TV monitor  302  (S 1 ). The TV monitor  302  answers the maker code and device code to the STB side  301  from the ROM table  412  (S 2 ). 
         [0077]    When the received maker code and device code have already been known, the STB  301  ends the protocol (S 3 ). On the other hand, when the received maker code and device code are unknown, the STB  301  asks the TV monitor  302  about the scanning rate the TV monitor  302  copes with (S 4 ). The TV monitor  302  answers the scanning rate at which it can perform scanning (S 5 ). 
         [0078]    Next, the STB  301  side asks the TV monitor  302  side what kind of audio the TV monitor  302  can reproduce (S 6 ). The TV monitor  302  side answers the number of channels of audio the TV monitor  302  can output (S 7 ). Thereby, the initial protocol between the STB  301  and the TV monitor  302  is ended. 
         [0079]    Next, it is supposed, as case  1 , that the STB  301  receives broadcasting having audio of 480i and 2-channel LR. In this case, by the negotiation of the previous initial access, the STB  301  knows that the TV monitor  302  can output 480i and 2-channel LR, and thus the audio of 480i and 2-channel LR is outputted to the TV monitor  302  side as it is, without being processed for display rate or sound. 
         [0080]    When, as case  2 , broadcasting of 1080i and 5.1-channel is received, since the STB  301  knows that the 1080i cannot be received by the connected TV monitor  302  by the negotiation of the initial protocol, the 1080i is converted into 480p on the STB  301  side. The conversion into 480p is performed because it is known by the previous negotiation that the TV monitor  302  can perform display at a display rate up to 480p. Further, it is also known that audio of 5.1 channel cannot be reproduced by the connected TV monitor, the 5.1 channel is down mixed to 2-channel LR on the STB  301  side. As the result, 480p is outputted as video data and down mixed 2-channel LR is outputted as audio data. 
         [0081]    Here, the ROM table  412  which is included in the I2C controller  411  in the TV monitor  302  will be described with reference to  FIG. 7 . For example, 4 bits indicating a displayable rate are stored at address 01 and, for example, in the case of a TV monitor which can display a signal of 480i and 29.97 Hz, a value of 0000 is entered in the ROM table  412 . Further, the number of channels of audio that can be outputted is stored at address 02 and, for example, a value of 0006 is entered when 6-channel decoding is possible. An address and a numeric value of such code are standardized in the industry. Thereby, even when the maker of the TV monitor is not known by the STB, since the minimum protocol is decided, it is possible to avoid the situation where no video image is displayed, a video image is displayed with an abnormal aspect, or no sound is outputted. That is, it is possible to avoid the problem that a video image cannot be displayed because the transmitting end transmits the video image with a frame rate at which the video image cannot be drawn-in at the PC monitor side or the TV monitor side, as in the conventional system. 
         [0082]    As described above, in the signal transmission system according to the third embodiment, since the STB outputs a video signal with the knowledge of the performance of the TV monitor, it is possible to avoid a problem that no video image is displayed or no sound is outputted at the TV monitor side, by performing the above-described negotiation, while in the conventional system the STB might output a rate at which the TV monitor cannot perform scanning. 
         [0083]    Further, when the TV monitor transmits its maker code and device code to the STB, if the maker code and device code fall in makers the information of which is disclosed between the STB and the TV monitor, it can be automatically selected, for example, whether an image should be up-converted by the STB or the TV monitor, by comparing performances of up-converting which are possessed by the STB and the TV monitor. 
         [0084]    Further, the initial access has been described taking the case where the negotiation is performed only for the type of scanning and the number of channels of reproducible audio. However, as another example of initial access, when it is known that the connected TV monitor is either a 16:9 wide TV or a 4:3 normal TV, letter box conversion or pan scan conversion is automatically performed at the STB side, whereby a correct aspect can automatically obtained. Accordingly, there is no need to set the connected monitor as to whether it is a wide TV or a normal TV, in the initial menu on the STB side, as in the conventional system. 
         [0085]    Further, generally, the TV monitor does not output a received signal as it is but enhances the signal with respect to the luminance and chrominance, and outputs it. However, there are cases where it is not desirable that a user of a personal computer manipulates the luminance and chrominance intentionally. In such cases, the characteristics of enhancement at the TV monitor side are notified to the STB side and the STB side outputs a video signal that is corrected inversely to the enhancement, whereby a non-enhanced video signal can be outputted to the TV monitor side in total. 
         [0086]    Further, when the TV monitor side is provided with a mode in which no enhancement is performed, reproduction with no chrominance enhancement can be secured by forcibly switching the TV monitor to that mode from the STB side. 
         [0087]    Further, when the connected monitor is a wide TV, there are generally display modes such as a wide mode and a normal mode on the TV side. For example, when a 16:9 monitor is connected and a material received by the STB is 16:9, the STB outputs the material as it is without performing aspect conversion. However, when the TV side is set at the normal display, what is actually circular might be displayed as longitudinal as shown on the right hand in  FIG. 6 . In this case, when the STB side sets the display mode of the TV side to a full display mode, a normal aspect image can be obtained. In  FIG. 6 , a diagram on the left hand shows a 16:9 picture which is normally expected to be outputted, and a diagram on the right hand shows a picture of an erroneous aspect when the TV side is erroneously set to a normal mode. 
         [0088]    Further, when signals to be transmitted between the STB and the TV monitor are not RGB signals but Y color-difference signals, i.e., YPBPR signals, a conversion formula for converting the YPBPR signals into the original RGB signals on the TV side may be different from that at the STB side and, therefore, the conversion formula itself can be also transmitted. As the conversion formula is described in MPEG stream data, the conversion formula extracted on the STB side is transmitted to the TV monitor side through the I2C, whereby the YPBPR signals can be converted into the normal RGB signals on the TV monitor side. 
         [0089]    Further, data transmission in the signal transmission system according to the third embodiment may be carried out such that data are multiplexed by employing a CTL0 or a CTL1 as a video signal line as shown in  FIG. 12 . 
       Embodiment 4 
       [0090]    Hereinafter, a signal transmission system according to a fourth embodiment of the present invention will be described with reference to  FIGS. 8 to 16 . 
         [0091]      FIG. 12  is a diagram illustrating the configuration of a selector provided in a video output interface at the transmitting end in the signal transmission system according to the fourth embodiment of the present invention. A difference from the third embodiment is that the video output interface  403  includes the selector. 
         [0092]    In  FIG. 12 , a selector  1201  temporally selects a red signal R and another control signal CTL0 by DE. A selector  1202  temporally selects a green signal G and a control signal CTL1. A selector  1203  temporally switches between a blue signal B and an HV sink signal. Here, the DE is a signal for discriminating between a scanning period and a retrace period of an image. 
         [0093]      FIG. 10  is a diagram for explaining the operation of the selector. While a description will be given of the selector  1201  here, the other selectors  1202  and  1203  are similarly operated and, therefore, descriptions thereof will be omitted. In  FIG. 10 , the DE signal becomes HIGH during the video period and becomes LOW during the retrace period. 
         [0094]    As the R signal and the CTL0 signal are inputted, the selector  1201  is operated to pass the R signal through when the DE signal is HIGH, while it is operated to pass the CTL0 signal through when the DE signal is LOW. Therefore, the output signal is the R signal during the video signal period while it is the CTL0 signal during the retrace period, which means control data can be transmitted. When the video rate of the output is interlacing, the retrace period becomes as shown on the left hand in  FIG. 8 . When the video rate of the output is progressive, it becomes as shown on the right hand in  FIG. 8 . 
         [0095]    The operation of the so-configured signal transmission system will be described with reference to  FIG. 9 . 
         [0096]    First of all, the STB asks the TV side about its maker code and device code (S 12 ). When the TV monitor side is a device which had been shipped before standardization, no answer is usually obtained for the asking about the maker code and the device code, and therefore, the processing is ended in this case, and the STB understands that the connected monitor does not support the function of TV monitor control through the I2C and decides that no control command will be sent through the I2C hereafter (S 13 ). 
         [0097]    On the other hand, when an answer is obtained for the asking about the maker code and device code, the STB checks whether or not the maker and device are of the types the STB has already known (S 14 ). In the case where the maker and device are of the known types, the processing is ended, and the connected monitor operates so as to change the output of the most suitable video and audio in combination with the STB itself since the performance of the connected monitor is known to the STB side (S 15 ). When it is judged in S 14  that the maker and device are of unknown types (UNKNOWN_TYPE), the rate at which display is possible and the number of audio channels are sequentially confirmed. Industrial standards should be created in advance for basic adjustment functions of adjusting volume, mute, brightness, contrast, etc., and the STB judges that these functions can be used. 
         [0098]      FIG. 11  shows an example of a construction of control data. For example, a piece of control data is composed of a header as a reservation pattern in which, for example, 01 continues for a 2-byte period, several bytes of R/W data for discriminating between writing from the STB to the TV and reading for reading the state on the TV side, an address on the TV side in which some value is written, and a value of the data to be written or read. As the control data is constituted as described above, a desired command can be sent to the TV side. 
         [0099]      FIG. 13  is a block diagram illustrating the configuration of the receiving end, that is, the TV monitor. 
         [0100]    In  FIG. 13 , numeral  1301  denotes a receiving TV monitor itself. Numeral  1302  denotes a video input interface, to which a video signal received thorough a transmission path is inputted. Numeral  1303  denotes a control data separation part, which separates only control data out of the video signal. Numeral  1304  denotes a temporary storage part, which temporarily stores the control data. Numeral  1305  denotes a picture quality control part, which corrects picture quality of the vide signal. Numeral  1306  denotes a device interface, which is an interface for a display device  1307 . Numeral  1308  denotes a CPU, which is used to control the picture quality control part  1305  with respect to a control signal from the control data separation part  1303 , which requires no real time property. Numeral  1309  denotes an I2C controller, which controls an I2C bus. Numeral  1310  denotes a ROM table in the I2C controller  1309 , where performance of the TV monitor  1301  is described. On the assumption that basic commands such as brightness, contrast, volume, and the like are standardized in the industry, such control data is interpreted by the CPU  1308 , and the CPU  1308  controls the picture quality control part  1305 . 
         [0101]    Since data attached to each frame is desired to be inputted to the picture quality control part  1305  without intervention of the CPU  1308 , the control signal to the picture quality control part  1305  is also outputted from the control data separation part  1303  directly. As an example of a control signal, there is information indicating that a decoded picture is any of I picture, P picture, and B picture, or whether a material of each frame is picked up by progressive scanning or interlaced scanning, or the like. 
         [0102]    As the receiving end is configured as described above, the TV monitor side can be operated with the minimum requirements such as brightness, contrast, and volume, which are control data from the STB. Further, as the STB transmits the control signal for each frame, it can control the picture quality for each frame. 
         [0103]      FIG. 14  is a diagram showing an example of a control signal to be transmitted for each frame. Here, a description will be given taking a case where telecine information is superposed, as an example. In the case of a telecine picture, there exists a field which is outputted repeatedly. Conventionally, a field memory is provided at the receiving end, and whether a field has been repeated or not is detected by taking a difference between fields, and scanning conversion is carried out. 
         [0104]      FIG. 15  is a block diagram illustrating a conversion circuit for converting a telecine material from 24p into 60p, for example. In  FIG. 15 , numerals  1501 ,  1502 , and  1503  denote field memories, and each field memory delays an input by one field and outputs it. A correlation calculation means  1504  examines correlation between a signal that is delayed by these filed memories and then inputted and the present signal, for each pixel. When there is correlation, the correlation calculation means  1504  judges that the present field has been repeated, and operates to control a selecting means  1505  which selects a field memory the output of which is to be outputted, from among the field memories. In the conventional field repeat detecting means, when the detecting accuracy is to be increased, the calculation of correlation becomes complicated, resulting in heavy hardware. Further, in the case where quite similar patterns are processed, erroneous detection cannot be avoided. 
         [0105]    To solve the above-described problems, in this embodiment a field repeat signal transmission system is employed as shown in  FIG. 16 . 
         [0106]    In  FIG. 16 , numeral  1601  denotes a MPEG decoder which decodes a broadcast wave and outputs a baseband video signal, and this MPEG decoder also outputs information as to whether a frame included in a stream of the broadcast wave is a top filed or a bottom field, and information as to whether a field has been repeated or not. Numeral  1602  denotes a transmission path encoding circuit, which encodes RGB signals outputted from the MPEG decoder  1601  into signals in the forms suited to the transmission path, and outputs the encoded signals during a scanning period, while superposes the top/bottom information and the field repeat information according to the form of the above-described control data during a retrace period. Numeral  1603  denotes a transmission path decoding circuit, which decodes the signals received through the transmission path into the original RGB signals, subjects the RGB signals to matrix conversion into Y color-difference signals, and outputs the Y color-difference signals. Numerals  1604 ,  1605 , and  1606  denote field memories, and each field memory delays a video signal by a field. Numeral  1607  denotes a retrace period code analysis means which extracts the information superposed on the control data. Numeral  1608  denotes a selecting means which receives output from the retrace period code analysis means  1607  and selects a field memory whose output is to be outputted. 
         [0107]    By the above described configuration, the retrace period code analysis means  1607  can reproduce, without errors, the top/bottom information and the field repeat information which have been superposed at the transmitting end, and therefore, a Y output signal can be obtained by employing the correct field repeat information and top/bottom information. 
         [0108]    Next, a description will be given of an output picture when conversion from 24p into 60p is performed on the monitor TV side employing these means and the picture is outputted, with reference to  FIG. 14 . In  FIG. 14 , numeral A1 denotes a first field of frame A, and numeral A2 denotes a second field of the same frame A. A TV monitor input signal is supposed to be a signal for example in which the A1 is followed by the A2 and then the field-repeated A1 comes again, temporally. In that case, a TV monitor output signal is a signal in which a frame composed of the A1 and the A2 is outputted and another frame composed of the A1 and the A2 similarly is outputted next. Here, when it is correctly detected that the third field of the input signal to the monitor is the same A1 as the first field, a correct picture composed of the A1 and the A2 is configured for the third frame of the TV monitor output signal. However, when there is erroneous detection at this time, the picture is not reproduced correctly. In this configuration as shown in  FIG. 16 , judgment is made on whether a field is repeated or not according to the top/bottom information and the field repeat information of the MPEG stream information superposed at the broadcasting end, whereby the output signal to the TV monitor is reproduced correctly. 
         [0109]    Further, in the fourth embodiment, the description has been given of the case where the field repeat information and the top/bottom information as the information relating to the telecine is superposed, for example information as to whether the frame is I picture, P picture, or B picture, may be similarly superposed. The I picture is an intra-frame encoded picture, the P picture is a picture that employs a difference between frames, and the B picture is a picture encoded by employing a bidirectional difference. Thereby, parameter setting for noise elimination can be performed for each frame. Conventionally, it is not known that each frame of a baseband video signal is the I picture, the B picture, or the P picture, whereby noise elimination cannot be performed adaptively. 
         [0110]    Further, as another example, information relating to the compression ratio of the MPEG may also be superposed. In this case, as for the compression ratio of the MPEG, a video stream of some megabits per second can be obtained from a header of an elementary stream of the MPEG. Further, horizontal/vertical sizes as well as a frame rate can be also obtained. Therefore, by notifying the TV side of a relationship between the horizontal/vertical sizes as well as the frame rate and a bit rate, a parameter for noise elimination can be set. In this way, it can be avoided that an appropriate processing cannot be performed since information relating to the compression ratio of the MGEG is not known to the transmitting end, as conventional. 
         [0111]    As another example, information as to whether a material is imaged by a progressive camera or an interlacing camera can be also known from the header of the MPEG stream, and thus this information can be transmitted as similar control data. This data can be utilized for selection of an IP conversion method, that is, a method of conversion from interlacing into progressive, on the TV monitor side. Conventionally, a motion detection circuit is required to perform correct IP conversion and this motion detection circuit is employed to perform progressive interpolation in a static area, while to perform interlacing interpolation in a moving image area. However, this motion detection circuit is not required here. Further, even when a material is interlacing, or when a graphics layer such as an OSD is superimposed on most of the screen, the progressive interpolation is appropriate. Whether the OSD or the like is superimposed or not is known inside the STB, and when the OSD or the like is superimposed, a control signal is subjected to the progressive interpolation and transmitted, thereby performing correct interpolation. 
         [0112]    Further, in data transmission in the signal transmission system according to the fourth embodiment, data with low transmission rate may be transmitted through the I2C bus shown in  FIG. 4 . 
         [0113]    Further, in the second embodiment, the color difference signals are multiplexed into a single signal, whereby the whole video signals can be transmitted through two transmission paths, while three signal lines are required in the first embodiment, and therefore a signal for discriminating a natural picture outputted from the MPEG decoder and an OSD area can be transmitted through the remaining signal line. By transmitting this signal, even when an error in IP conversion occurs during broadcasting of 480p, the broadcasting of the 480p data is not adversely affected and display with high picture quality is possible. Further, characters and natural pictures can be processed separately for each pixel. 
         [0114]    Further, in the second embodiment, only two transmission paths are required, whereby the remaining transmission path can be defined as a user-defined signal line. 
         [0115]    Further, the description has been given of the case where a unit which outputs the video signal is the STB in  FIG. 4 , just the same configuration can be applied to a case where the unit is a digital camera or a notebook computer which requires power saving. In the case of a mobile terminal such as a digital camera or a notebook computer, a static picture is transmitted, and thus when a memory is held in the video input interface  408  on the TV monitor side or for example in the picture quality control part  1305  in the TV monitor body, presence or absence of the memory and capacity of the memory are first confirmed by 11C bus control or control employing the CTL0 or the CTL1, then a controlling side (mobile terminal side) instructs the TV monitor side of storage into the memory, and the controlling side (mobile terminal side) transmits a picture or pictures in the number within the memory capacity of the TV monitor side to the TV monitor side through the video output interface  403  at the instruction of a user. The TV monitor side stores a video image set by the user in the video input interface  408  on the TV monitor side or for example in the picture quality control part  1305  in the TV monitor body. When the TV monitor side is found not to have a memory by the confirmation of the presence or absence of the memory in the first step, a video signal is always outputted as well as a motion picture. Further, in the case of a PC, the same control is performed every time a video image inside is changed, and thus static data is transmitted in the above-described sequence when a change occurs in the video image of the PC. By this construction, a static image held on the TV monitor side can be continuously displayed on the TV monitor side without re-transmitting the same static picture continuously from the mobile terminal such as a digital camera or a notebook computer. Therefore, the video output interface in the digital camera as a video signal generating end is required to operate only when transmitting a static picture, resulting in power saving. By temporally repeating this static picture transmission, for example by repeatedly transmitting a static picture and stopping the transmission every second, a picture such as a motion JPEG can be efficiently transmitted with saved power. 
         [0116]    A signal transmission system according to the present invention, in one embodiment comprises: a signal transmission unit ( 101 ) that includes a MPEG decoder ( 103 ) which receives digital broadcasting and outputs a luminance signal Y and two color difference signals PB/PR, and a transmission path encoding circuit ( 103 ) which encodes the YPBPR outputted from the MPEG decoder ( 102 ) into signals in the forms suited to a transmission path and transmits the encoded signals; and a signal reception unit ( 104 ) that includes a transmission path decoding circuit ( 105 ) which receives the encoded YPBPR and decodes them, a Y processing circuit ( 106 ) which processes the decoded luminance signal Y, a chrominance processing circuit ( 107 ) which processes the respective decoded color difference signals PB/PR, a signal conversion circuit ( 108 ) which converts the YPBPR outputted from the Y processing circuit ( 106 ) and the chrominance processing circuit ( 107 ) into RGB signals, and a display device ( 108 ) which displays the RGB signals. According to the so-configured signal transmission system, it is possible to realize a signal transmission system in which hardware configurations of the video signal transmitting end and receiving end can be simplified. 
       APPLICABILITY IN INDUSTRY  
       [0117]    A signal transmission system according to the present invention is available as a signal transmission system which has its configuration simplified and is capable of controlling a signal receiving unit from a signal transmission unit. 
         [0118]    While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.