Abstract:
In prior art documents, no consideration is given as to how to more faithfully preserve image (here and subsequently also termed “video”) data of larger size during transmission. Provided is an image transmission device for transmission of image data, characterized by having a compression processor for compressing image data, and an output section for outputting compressed data having been compressed by the compression processor, the output section outputting the compressed data separately during a first interval and a second interval different from the first interval.

Description:
TECHNICAL FIELD 
       [0001]    The technical field relates to transmission and reception of image information. 
       BACKGROUND ART 
       [0002]    In recent times, the number of pixels handled by digital image processing is increasing from year to year in connection with the adoption of 4k2k (3840×2160 pixels) for displays for general users, HD (High Definition: 1920×1080 pixels) for broadcasting and high pixel capacities for image sensors and displays of digital video cameras. 
         [0003]    Regarding formulas of transmitting such image data between equipment units, there are the HDMI (High-Definition Multimedia Interface (registered trademark of HDMI Licensing, LLC) standards and DisplayPort (registered trademark or trademark of VESA) standards formulated by VESA (Video Electronics Standards Association). 
         [0004]    Regarding the aforementioned HDMI data transmission formula, Patent Literature 1 states that it is “to selectively transmit uncompressed image signals or compressed image signals obtained by subjecting these uncompressed image signals to compression processing by a compression formula compatible with the receiver device, and permits satisfactory transmission of image signals at a desired bit rate within the transmission bit rate range of the transmission path” (see [ 0048 ] in Patent Literature 1) and, regarding the compression formula, “the data compressors  121 - 1  to  121 - n  process compression, at a prescribed compression rate, of uncompressed image signals outputted from the codec  117  and outputs compressed image signals. The data compressors  121 - 1  to  121 - n  constitute an image signal compressing unit. Each of the data compressors  121 - 1  to  121 - n  processes data compression by a different compression formula from all the others. For instance, it is stated that, as compression formulas, “‘RLE (Run Length Encoding)’, ‘Wavelet’, ‘SBM (Super Bit Mapping (trademark of Sony))’, ‘LLVC (Low Latency Video Codec)’, ‘ZIP’ and so forth are conceivable” (see [ 0077 ] in Patent Literature 1). 
         [0005]    Further in HDMI, data transmission formats of TMDS (registered trademark of Transition Minimized Differential Signaling (Silicon Image, Inc.)) are used for image data, and Patent Literature 2 is cited as one example. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Patent Application Laid-Open No. 2009-213110 
         Patent Literature 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-514873 
       
     
       Technical Problem 
       [0008]    However, in any of the cited prior literature, no consideration is given to transmissions of images (sometimes referred to as “pictures”; the same applies hereinafter) of larger sizes while keeping the data more faithfully. 
       Solution to Problem 
       [0009]    To solve the problem noted above, for instance configurations described in the Claims are used. 
       Advantageous Effects of Invention 
       [0010]    Whereas the present application covers a plurality of means to solve the problem, according to one example of the means, there is provided an image transmission device that transmits image data including a compression processor that compresses image data and an output section that outputs compressed image data compressed by the compression processor, wherein the output section outputs the compressed image data divided between a first period and a second period different from the first period. 
         [0011]    To cite another example, an image transmission device that transmits image data includes a compression processor that processes compression of image data including a plurality of components, and a data transmission section that outputs the compressed image data, wherein the data transmission section alters the outputting method of image data on the basis of the individual components of the image data. 
         [0012]    To cite still another example, an image transmission device that transmits image data includes a compression processor that processes compression of image data and generates compressed image data and compression coding information concerning the compression processing, and a data transmission section that outputs compressed image data and the compression coding information, wherein the redundancy of the compression coding information is greater than the redundancy of the compressed image data. 
         [0013]    To cite yet another example, an image transmission device that transmits image data includes a compression processor that processes compression of image data and an compressed by the compression processor, wherein the output section outputs the compressed image data divided between a first period and a second period different from the first period, and the compression processor alters, on the basis of the transmission error rate on a transmission path, compression processing of the image data. 
         [0014]    By the means described above, it is made possible to transmission image data of a greater size while keeping the data more faithfully. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  shows one example each of an image transmission device and an image receiving device of a first embodiment. 
           [0016]      FIG. 2  shows one example of valid/blanking period of the image data in the first embodiment. 
           [0017]      FIG. 3  shows one example of units of image data to be compressed in the first embodiment. 
           [0018]      FIG. 4  shows another example of units of image data to be compressed in the first embodiment. 
           [0019]      FIG. 5  shows one example of composition of main compression coding information, auxiliary compression coding information and compressed image data in the first embodiment. 
           [0020]      FIG. 6  shows one example of data transmission timing in the first embodiment. 
           [0021]      FIG. 7  shows one example of compression processor in the first embodiment. 
           [0022]      FIG. 8  shows another example of compression processor in the first embodiment. 
           [0023]      FIG. 9  shows another example of compression processor in the first embodiment. 
           [0024]      FIG. 10  shows one example of compressor A in the first embodiment. 
           [0025]      FIG. 11  shows one example of compressor A in the first embodiment. 
           [0026]      FIG. 12  shows one example of error correction code generator in the first embodiment. 
           [0027]      FIG. 13  shows one example of data transmission section in the first embodiment. 
           [0028]      FIG. 14  shows one example of header of a compression coding information packet in the first embodiment. 
           [0029]      FIG. 15  shows one example of data of the compression coding information packet in the first embodiment. 
           [0030]      FIG. 16  shows another example of header of the compression coding information packet in the first embodiment. 
           [0031]      FIG. 17  shows another example of data of the compression coding information packet in the first embodiment. 
           [0032]      FIG. 18  shows one example of compression coding information packet in the first embodiment. 
           [0033]      FIG. 19  shows one example of EDID statement of the image receiving device in the first embodiment. 
           [0034]      FIG. 20  shows one example of data reception processor in the first embodiment. 
           [0035]      FIG. 21  shows one example of expansion processor in the first embodiment. 
           [0036]      FIG. 22  shows another example of expansion processor in the first embodiment. 
           [0037]      FIG. 23  shows another example of expansion processor in the first embodiment. 
           [0038]      FIG. 24  shows another example of expansion processor in the first embodiment. 
           [0039]      FIG. 25  shows one example of data transmission timing in the first embodiment. 
           [0040]      FIG. 26  shows another example of data transmission timing in the first embodiment. 
           [0041]      FIG. 27  shows one example of compression coding information in the first embodiment. 
           [0042]      FIG. 28  shows another example of compression coding information in the first embodiment. 
           [0043]      FIG. 29  shows one example of waveform of a serializer in a second embodiment. 
           [0044]      FIG. 30  shows one example of data composition of the serializer output in the second embodiment. 
           [0045]      FIG. 31  shows one example of packet composition of audio data in the second embodiment. 
           [0046]      FIG. 32  shows one example of bit allocation to various components of compressed image data on a transmission path in the second embodiment. 
           [0047]      FIG. 33  shows another example of bit allocation to various components of compressed image data on a transmission path in the second embodiment. 
           [0048]      FIG. 34  shows another example of bit allocation to various components of compressed image data on the transmission path in the second embodiment, 
           [0049]      FIG. 35  shows another example of bit allocation to various components of compressed image data on the transmission path in the second embodiment. 
           [0050]      FIG. 36  shows another example of bit allocation to various components of compressed image data on the transmission path in the second embodiment. 
           [0051]      FIG. 37  shows another example of bit allocation to various components of compressed image data on the transmission path in the second embodiment. 
           [0052]      FIG. 38  shows another example of bit allocation to various components of compressed image data on the transmission path in the second embodiment. 
           [0053]      FIG. 39  shows one example of data composition of main compression coding information in a third embodiment when no redundancy level is added. 
           [0054]      FIG. 40  shows one example of data composition of main compression coding information in the third embodiment when a redundancy level is added. 
           [0055]      FIG. 41  shows another example of data composition of main compression coding information in the third embodiment when the redundancy level is added. 
           [0056]      FIG. 42  shows another example of data composition of main compression coding information in the third embodiment when the redundancy level is added. 
           [0057]      FIG. 43  shows one example of data composition of auxiliary compression coding information in the third embodiment when the redundancy level is added. 
           [0058]      FIG. 44  shows one example of allocation of compression rate, horizontal blanking period and redundancy level relative to the transmission error rate in a fourth embodiment. 
           [0059]      FIG. 45  shows another example of allocation of compression rate, horizontal blanking period and redundancy level relative to the transmission error rate in the fourth embodiment. 
           [0060]      FIG. 46  shows another example of allocation of compression rate, horizontal blanking period and redundancy level relative to the transmission error rate in the fourth embodiment. 
           [0061]      FIG. 47  shows one example of allocation of compression rate, horizontal blanking period and redundancy level relative to the contents in a fifth embodiment. 
           [0062]      FIG. 48  shows one example of main compression coding information, auxiliary compression coding information and compressed image data, and transmission timing of audio packet in a sixth embodiment. 
           [0063]      FIG. 49  shows another example of main compression coding information, auxiliary compression coding information and compressed image data, and transmission timing of audio packet in the sixth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0064]    Known systems of transmitting image data to minimize the delay time include an uncompressed image data transmission system, but it has involved the problem of requiring a high-transmission path if sending large-size image data is intended. To solve this problem a system of transmitting image data in a compressed form is proposed, but it has its own problem that, once an error arises on the transmission path, displayed images are disturbed in compressed block units, each including a plurality of pixels. There has been another problem that the data quantity that can be transmitted during a blanking period in which high error-resistivity is ensured is smaller than that can be transmitted during a valid pixel period. 
         [0065]    In the following embodiments, solution of this problem is attempted by accomplishing data compression in compressed block units in a system of transmitting image data under compression to generate compression coding information and transmitting a more important part of the compression coding information out of the generated compression coding information (hereinafter to be referred to as main compression coding information) in a blanking period in which error-resistivity is higher. To add, other parts of the compression coding information (hereinafter to be referred to as auxiliary compression coding information), like compressed image data, are transmitted during a valid period. These embodiments will be described below with reference to drawings. 
       Embodiment 1 
       [0066]    The modes of materializing image transmission devices and image receiving devices in these embodiments will be described below. 
         [0067]      FIG. 1 , a block diagram illustrating the image transmission system of this embodiment, shows a configuration connecting image transmitting device  100  and an image receiving device  200  by a cable  300 . 
         [0068]    The image transmitting device  100  is an image transmitting device, an equipment item that transmits image data, outputting to another equipment item over an HDMI cable or the like image data obtained by receiving digital broadcasts, decoding them into a visible and audible form, image data recorded on a recording medium or image data photographed with a camera or the like. Examples of the image transmitting device  100  include recorders, digital TV sets with a built-in recording function, personal computers with a built-in recorder function, and mobile telephones or camcorders mounted with a camera function and a recorder function. 
         [0069]    The image receiving device  200  is a display device that uses an HDMI cable or the like to receive inputs of image data and outputs images on a monitor. Examples of the image receiving device  200  include digital TV sets, display sections, projectors, mobile telephones and signage equipment. 
         [0070]    The cable  300  is a data transmission path for carrying out data communication, such as that of image data between the image transmitting device  100  and the image receiving device  200 . Examples of the cable  300  include a wire cable satisfying the HDMI standards or the DisplayPort standards, and a data transmission path for wireless data communication. 
         [0071]    First, the configuration of the image transmitting device  100  will be described. 
         [0072]    Input sections  101 ,  102  and  103  are input sections for inputting image data to the image transmitting device  100 . One example of image data inputted to the input section  101  and processed by a tuner reception processor  105  is a digital broadcast inputted as electric waves from a relay station of a broadcasting station, a broadcast satellite or the like. To the input section  101 , such electric waves from a relay station of broadcasting station, a broadcast satellite or the like are inputted. 
         [0073]    One example of image data inputted to the input section  102  and processed by a network reception processor  106  is a digital broadcast or information contents distributed via a network by using broadband connection of the Internet. 
         [0074]    One example of image data inputted to the input section  103  and processed by a medium controller  107  is contents recorded on an external recording medium connected to the input section  103 . Another example of image data processed by the medium controller  107  is contents recorded in a recording medium  108  built into the image transmitting device  100 . Examples of the recording medium  108  include an optical disk, a magnetic disk and a semiconductor memory. 
         [0075]    The tuner reception processor  105  is a reception processor that converts an inputted electric wave into a bit stream, and it subjects the electric wave of the RF (Radio Frequency) band to frequency conversion to the IF (Intermediate Frequency) band and demodulates the modulation applied to the demodulated bit stream as signals of a certain band not dependent on the reception channel. 
         [0076]    Examples of bit stream include an MPEG2 transport stream (hereinafter referred to as MPEG2-TS) and a bit stream of a format complying with MPEG2-TS. Descriptions of bit stream in the following paragraphs will refer to MPEG2-TS as a representative one. 
         [0077]    The reception processor  105  further detects and corrects any code error having arisen on the way of transmission and, after descrambling the MPEG2-TS, selects one transponder frequency at which programs for playing back or recording are multiplexed, and separates a bit stream in this selected one transponder into one program of audio and a video packet. 
         [0078]    The MPEG2-TS from the tuner reception processor  105  is supplied to a stream controller  111  via a data bus  181 . The stream controller  111 , to keep the intervals at the time packet reception by the tuner reception processor  105 , detects PTS (Presentation Time Stamp), which is a time management information item, and an STC (System Time Clock) within a reference decoder of the MPEG system, and adds a time stamp at a timing corrected according to the result of detection. 
         [0079]    The time stamp-augmented packet is supplied to either a decoder section  112  or the recording medium controller  107  or to both. A data path  194  to the decoder section  112  is used for processing when image data are to be played back, and a data path  193  to the recording medium controller  107  is used when recording image data onto a recording medium, 
         [0080]    To a data path  192  of the stream controller  111 , the MPEG2-TS coming from the input section  102  via the network reception processor  106  is inputted. The data path  192  is an input section that acquires a digital broadcast or digital contents distributed via a network. 
         [0081]    Further, an external recording medium connected to the input section  103 , or a digital broadcast or digital contents recorded on the recording medium  108  built into the image transmitting device  100  is read out as the MPEG2-TS by the recording medium controller  107 , and inputted to the stream controller  111  via the data path  193 . The stream controller  111  selects at least one of these inputs, and outputs it or them the decoder section  112 . 
         [0082]    The decoder section  112  decoded the MPEG2-TS inputted from the stream controller  111 , and outputs the thereby generated image data to a display processor  113 . The display processor  113 , after subjecting the inputted image data to, for instance superposition of OSD (On Screen Display), rotation, expansion or contraction, or frame rate conversion, outputs the processed data to a compression processor  114 . 
         [0083]    The compression processor  114  compresses the image data from the display processor  113 , and outputs the compressed data to a data transmission section  115 . 
         [0084]    The data transmission section  115  converts the image data compressed by the compression processor  114  (hereinafter to be referred to as compressed image data) into signals in a form suitable for transmission, and outputs it from an output section  116 . Regarding the transmission of the image data, one example of signals in a form suitable for transmission is described in the HDMI standards. In HDMI, a data transmission format of the TMDS system is adopted for image data. 
         [0085]    An input section  104  is an input section for inputting signals for controlling the operation of the image transmitting device  100 . Examples of the input section  104  include a receiver unit for signals transmitted from a remote controller and a button fitted onto a device body. Control signals from the input section  104  are supplied to a user IF  109 . The user IF  109  outputs signals from the input section  104  to a controller  110 . The controller  110  controls the whole image transmitting device  100  in accordance with signals from the input section  104 . One example of the controller  110  is a microprocessor. The image data from the image transmitting device  100  is supplied to the image receiving device  200  via the cable  300 . 
         [0086]    Next, the configuration of the image receiving device  200  will be described. 
         [0087]    Signals in a form suitable for cable transmission are inputted to an input section  201 . The signals inputted to the input section  201  are supplied to a data reception processor  205 . 
         [0088]    The data reception processor  205  performs processing conversion of signals in a form suitable for cable transmission into prescribed digital data, and outputs the converted digital data to an expansion processor  206 . 
         [0089]    The expansion processor  206  expands the compression processing accomplished with the compression processor  114  in the image transmitting device  100  to generate image data, and outputs the processed data a display processor  207 . 
         [0090]    The display processor  207  subjects the inputted image data to display processing. Examples of display processing include OSD superposition, expansion or contraction for conversion into the resolution of a display section  208 , rotation and frame rate conversion. The output of the display processor  207  is supplied to the display section  208 . 
         [0091]    The display section  208  converts the inputted image data into signals matching the display system and displays the converted signals on a screen. Examples of the display section  208  include a liquid crystal display, a plasma display, an organic EL (Electro-Luminescence) display and a projector-projected display. 
         [0092]    An input section  202  is an input section for inputting signals for controlling the operation of the image receiving device  200 . Examples of the input section  202  a receiver unit for signals transmitted from a remote controller and a button fitted onto a device body. Control signals from the input section  202  are supplied to a user IF  203 . The user IF  203  outputs signals from the input section  202  to a controller  204 . The controller  204  is a controller that controls the whole image transmitting device  200  in accordance with signals from the input section  202 . 
         [0093]      FIG. 2  shows a valid period in which image data of one frame period are transmitted and a blanking period in which no image data are transmitted. 
         [0094]    The area denoted by  400  represents a vertical period, and the vertical period  400  includes a vertical blanking period  401  and a vertical valid period  402 . A VSYNC signal is a one-bit signal, 1 representing a period of the prescribed number of lines from the beginning of the vertical blanking period  401  and 0 representing a period between any other vertical blanking period and a vertical valid period  402 . One example of prescribed number of lines is four lines. 
         [0095]    The area denoted by  403  represents a horizontal period, and the horizontal period  403  includes a horizontal blanking period  404  and a horizontal valid period  405 . An HSYNC signal is a one-bit signal, 1 representing a period of the prescribed number of signal is a one-bit signal, 1 representing a period of the prescribed number of from the beginning of the horizontal blanking period  404  and 0 representing a period between any other horizontal blanking period and a horizontal valid period  405 . One example of prescribed number of pixels is 40 pixels. 
         [0096]    A valid period  406  is the area surrounded by the vertical valid period  402  and the horizontal valid period  405  and image data are allocated to this period. Further, a blanking period  407  is the area surrounded by the vertical blanking period  401  and the horizontal blanking period  404 . 
         [0097]    In this embodiment in this configuration, compressed image data and auxiliary compression coding information are transmitted in the valid period  406  and main compression coding information are transmitted in the blanking period  407 . 
         [0098]    In the blanking period  407 , audio data and other incidental data are transmitted in a packetized form. 
         [0099]    A method of reliably transmitting this packet containing audio data and the like in the blanking period  407  is disclosed, in for instance, the Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-514873. 
         [0100]    As error correction codes are included in packeted data in the blanking period in this configuration, errors arising on the transmission path can be corrected, resulting in strengthened error resistance. Further, as the configuration is such that the data to be transmitted in the packeted form during the blanking period is transmitted over two physically different channels, and the transmission channel is switched over at prescribed intervals of time, an error having arisen on one channel in a burst mode does not affect the pother channel, data errors can be corrected. The correction rate of errors is sufficient to achieve an improving effect of 10 −14  in the horizontal blanking period against 10 −9  in horizontal valid period. 
         [0101]    In this example, 24 bits of image data per clock are transmitted during the valid period  406 , and in the blanking period  407  one packet including a 3-byte header and 28-byte data is transmitted in a 32-clock period. 
         [0102]    For instance, when 12 bits each of signals of horizontal 3840 valid pixels, vertical 2160 valid lines and YCbCr luminance chromatic difference are to be transmitted in the 444 format at a frame frequency of 60 Hz, a very high clock frequency of 891 MHz is required. A high clock frequency not only needs a costly transmission and reception units but also entails a decrease in cable length permitting stable transmission of images, resulting in inconvenience in use. 
         [0103]    This embodiment makes it possible to approach a practically useful clock frequency, 594 MHz by 2/3 compression or 297 MHz by 1/3 compression. Further by the 444 format of 8 bits each the 422 format of 12 bits each of YCbCr luminance chromatic difference signals, a practically useful clock frequency of 297 MHz can be achieved by 1/2 compression. 
         [0104]    Where there are 3840 horizontal valid pixels and 2160 vertical valid lines, for instance, the horizontal blanking period has 560 horizontal blanking pixels and the vertical blanking period has 90 vertical blanking lines. The following description will refer to a case of compressing 12 bits each of YCbCr luminance chromatic difference image signals in the 444 format of 3840 horizontal valid pixels, 2160 vertical valid lines and 60 Hz frame frequency are compressed to 1/3 by way of example. 
         [0105]    The clock frequency after compression is 297 MHz and, in a transmission under the conditions of 1940 horizontal valid pixels, vertical 2160 valid lines, 280 horizontal blanking pixels and 90 vertical blanking lines, permits easy reproduction of the original clock of 594 MHz, double the transmission frequency, on the receiving side on a stable basis. During the period of horizontal valid pixels if 12 bits of YCbCr luminance chromatic difference signals per pixel, or a total of 36 bits are compressed to 1/3, namely 12 bits, 24 bits per pixel after the compression can be transmitted, and therefore two pixel-equivalent of the original pixel can be transmitted, resulting in halving of the original clock frequency after the compression. 
         [0106]    Since one packet per 32 clocks can be transmitted, a maximum of eight packets of 280 compressed horizontal blanking pixels can be transmitted. On the other hand, 24 bits×8 ch of audio data per packet can be transmitted. As the horizontal frequency of image data is 135 kHz (=60 Hz×(2160+90)), when 24 bits of linear PCM audio data of 192 kHz samples are to be transmitted over 8 ch, a maximum of two packets is required in one horizontal blanking period. It is desirable that, for the remaining six packets, compression coding type information can be stated within 168 bytes (=28 bytes×6 packets). 
         [0107]    On the other hand, when the aforementioned 32 pixels are to be compressed as a unit block, a stating space for YCbCr luminance chromatic difference signals equivalent to 120 blocks of information of different compression coding systems, or an equivalent of 360 blocks in total, is needed because there are 3840 horizontal valid pixels. If the main compression coding information is expressed in three bits for instance, the stating space will be equivalent 135 bytes, permitting transmissions of five packets, and it can be compatible with a large capacity audio data transmission of 192 kHz, 8 ch. 
         [0108]      FIG. 3  and  FIG. 4  show examples of image data inputted to the compression processor  114 . Luminance signals of n pixels in the horizontal direction and m lines in the vertical direction are shown. Chromatic difference signals, in the case of the 444 format, take on the same format as luminance signals. Examples of the number of pixels n and the number of lines m include a so-called full HD image of n=1920, m=1080, and a so-called 4k2k image of n=3840, m=2160. 
         [0109]    Here, the unit block of image data compressed by the compression processor  114  (hereinafter to be referred to as compressed block) shall be 1 pixels in the horizontal direction and k pixels in the vertical direction. In  FIGS. 3 ,  501  and  502  represent cases of l=32, k=1, and are configured of 32 consecutive pixels on the same line. In this image data unit, the compression processor  114  carries out compression. 
         [0110]    In  FIGS. 4 ,  503  and  504  represent cases of l=16, k=2, and are configured of 16 consecutive pixels on two lines, upper and lower. In this image data unit, the compression processor  114  carries out compression. For compression processing, the configuration may as well have a horizontal compressor and a vertical compressor, k1 and k2 (k1&lt;k2) image data unit blocks made available, differing in the pixel number k in the vertical direction, and the horizontal compressor and the vertical compressor  134  respectively compressing the k1 image data unit blocks and the k2 image data unit blocks. 
         [0111]    Although a case of 32 pixels has been described as an example of image data unit to be compressed, the unit may as well be 64 pixels or 128 pixels. 
         [0112]    When the inputted chromatic difference signals are in the 422 format, the data will have one pixel each of the Cb component and the Cr component of the chromatic difference signals alternately. For instance in a 4k2k image, they may as well be treated as image data of n=3840, m=2160 in the total of Cb components and Cr components. Since the correlation level is high among Cb components and among Cr components, the efficiency of compression can be enhanced by separating Cb components and Cr components from each other, treating either as components of n=1920, m=2160 and making them an image data unit block of only the same components to be compressed. 
         [0113]    When the inputted chromatic difference signals are in the 420 format, the data will have one pixel each of the Cb component and the Cr component of the chromatic difference signals for four pixels of Y signals. For instance in a 4k2k image, they may as well be treated as image data of n=1920, m=2160 in the total of Cb components and Cr components. Since the correlation level is high among Cb components and among Cr components, the efficiency of compression can be enhanced by separating Cb components and Cr components from each other, treating either as components of n=1920, m=2160 and making them an image data unit block of only the same components to be compressed. 
         [0114]    The compression coding information is configured of main compression coding information and auxiliary compression coding information. On the basis of the main compression coding information and the auxiliary compression coding information, expansion of compressed image data to the original image data can be processed. 
         [0115]    With only main compression coding information, simple expansion or partial expansion can be processed. 
         [0116]    Main compression coding information is transmitted over a transmission path higher in error-resistivity than that for auxiliary compression coding information. In this embodiment, compressed image data and auxiliary compression coding information are transmitted to the valid period  406 , and main compression coding information is transmitted to the blanking period  407 . As an example of transmitting main compression coding information in the blanking period  407 , there is a method by which common main compression coding information is transmitted in the vertical blanking period  401  line by line, main compression coding information on compressed blocks on the same line is transmitted in the horizontal blanking period  404 . 
         [0117]    Where this configuration is used, even if an error occurs in auxiliary compression coding information on a transmission path of a high transmission error rate, the probability of error occurrence in main compression coding information is significantly reduced. As a result, when an error has occurred in auxiliary compression coding information on a transmission path of a high transmission error rate, disturbance of display can be restrained by using simply expanded or partially expanded image data, created by utilizing main compression coding information, for error correction. Also, by including the compressed block size in main compression coding information when an error has occurred in auxiliary compression coding information, disturbance of display can be restrained within the compressed block. 
         [0118]    Further, compression coding information may as well be configured solely of main compression coding information or auxiliary compression coding information. 
         [0119]    An example of configuration of compression coding information and compressed image data is shown in  FIG. 5 . 
         [0120]    In this example, the unit of a compressed block  600  is configured of sub-compressed blocks  610  and  620 , and the sub-compressed block blocks  610  and  620  are configured of pixels  611 ,  612 ,  613  and  614  and pixels  621 ,  622 ,  623  and  624 , respectively. 
         [0121]    One example of configuration of a compressed block after compression is represented by  630 . The compressed block  630  is configured of compression coding information  631  and compressed image data  632 . The compressed image data  632  is a compressed image data set generated by compressing pixel data sets  611 ,  612 ,  613 ,  614 ,  621 ,  622 ,  623  and  624 . The compression coding information  631  is information generated by compression processing. When compression coding information is transmitted in the valid period  406  in this configuration, if the transmission error rate is high, the probability of error occurrence also in the compression coding information increases, entailing a problem that display disturbance becomes more likely to arise in compressed block units. Further, when compression coding information is transmitted in the blanking period  407 , the quantity of transmittable data becomes significantly smaller than in the valid period  406 , entailing a problem of reduction in the quantity of compression coding information. 
         [0122]    Another example of configuration of a compressed block after compression is represented by  640 . In this example, compression coding information is configured of main compression coding information  641  and two kinds of auxiliary compression coding information  642  and  644 . The compressed block  640  is configured of the main compression coding information  641 , the auxiliary compression coding information sets  642  and  644 , and compressed image data sets  643  and  645 . The compressed image data  643  is a compressed image data set generated by compressing the image data sets  611 ,  612 ,  613  and  614  belonging to the sub-compressed block  610 . The auxiliary compression coding information  642  is an information set generated by processing compression of the pixel data sets  611 ,  612 ,  613  and  614 . The compressed image data set  645  is a compressed image data set generated by compressing the image data sets  621 ,  622 ,  623  and  624  belonging to the sub-compressed block  620 . The auxiliary compression coding information  644  is an information set generated by processing compression of the pixel data sets  621 ,  622 ,  623  and  624 . 
         [0123]    Another example of configuration of a compressed block after compression is represented by  650 . In this example, compression coding information is configured of two kinds of information including main compression coding information  651  and auxiliary compression coding information  652 . The compressed block  650  is configured of the main compression coding information  651 , the auxiliary compression coding information  652  and compressed image data  653 . The compressed image data  653  is a compressed image data set generated by compressing the image data sets  611 ,  612 ,  613 ,  614 ,  621 ,  622 ,  623  and  624  contained in the compressed block  600 . The main compression coding information  651  and the auxiliary compression coding information  652  are information sets generated by processing compression of the compressed block  600 . 
         [0124]    Another example of configuration of a compressed block after compression is represented by  660 . The difference between this example and the compressed block  650  after compression lies in that auxiliary compression coding information  662  is information generated by further compressing the auxiliary compression coding information  652  in the compressed block  650  after compression. Though not illustrated here, the quantity of transmitted data may be reduced by further compressing the main compression coding information  651 . 
         [0125]    Where the aforementioned configuration of the compressed blocks  640 ,  650  and  660  after compression is adopted, it becomes possible to restrain the influence of any transmission error on the displayed image (restored image) while suppressing the quantity of data transmitted over the more error-resistive transmission path by transmitting main compression coding information over a more error-resistive transmission path than auxiliary compression coding information. 
         [0126]      FIG. 6  illustrates the transmission timing for the compressed blocks  640 ,  650  and  660  after compression shown in  FIG. 5 . Reference numerals  700  and  702  denote the valid period  406 , and  701  denotes the horizontal blanking period  404 . Reference numerals  710 ,  711  and  712  denote one line-equivalent of image data before compression to be transmitted in the valid period  700 . In this example, the three compressed blocks  710 ,  711  and  712  are processed for compression. 
         [0127]    Reference numeral  730  denotes main compression coding information generated by processing compression of the compressed blocks  710 ,  711  and  712 . Reference numerals  731 ,  732  and  733  denote compressed blocks generated by processing compression of the compressed blocks  710 ,  711  and  712 . The compressed blocks are configured of compressed image data and auxiliary compression coding information generated by compression processing. As one example of the configuration of the compressed block  731 ,  740 ,  750  and  760  are shown. They respectively correspond to the sub-compressed blocks  640 ,  650  and  660  after compression shown in  FIG. 5 . 
         [0128]    The main compression coding information  730  is transmitted in the horizontal blanking period  701 , which is more error-resistive than the valid periods  700  and  702 . Further, the compressed blocks  731 ,  732  and  733  after compression configured of compressed image data generated by processing compression of the image data  710  and auxiliary compression coding information are transmitted over the valid period  702 , next to the horizontal blanking period  701 . To add, some or all of main compression coding information may as well be transmitted in the vertical blanking period  401 . 
         [0129]    One example of main compression coding information and auxiliary compression coding information will be described with reference to  FIG. 28 . 
         [0130]    Here is considered a case of compression processing in which the unit of compressed blocks  920  is 32 horizontal pixels and that of sub-compressed blocks  921 ,  922 ,  923  and  924  is 8 pixels. Compression coding information  926  for the leading sub-compressed block  921  is supposed to be main compression coding information, and compression coding information sets  927 ,  928  and  929  for the other three sub-compressed blocks are supposed to be auxiliary compression coding information. 
         [0131]    The main compression coding information is configured of the compression coding information  926  for the leading sub-compressed block  921  and other compression coding information sets for use in the processing to expand the sub-compressed block  921  (for instance the common compression coding information  925  for the sub-compressed blocks and the like). 
         [0132]    The auxiliary compression coding information is configured of the compression coding information sets  927 ,  928  and  929  for the second and subsequent sub-compressed blocks  922 ,  923  and  924 . 
         [0133]    The use of the configuration of this example enables display disturbance to be restrained by using, when an error has occurred in the auxiliary compression coding information on a transmission path of a high transmission error rate, image data belonging to the leading sub-compressed block expanded by the use of the main compression coding information for correction of the error. One example of such error correction is generating and displaying a complementing image belonging to the error-ridden sub-compressed block from image data belong to the leading sub-compressed block out of the compressed blocks expanded by the use of the main compression coding information. 
         [0134]    One example pertinent to the transmission path is a method by which auxiliary compression coding information ( FIG. 28(   c )) and a compressor output ( FIG. 28(   d )) are transmitted in the valid period  406  and main compression coding information is transmitted in the horizontal blanking period  404  greater in error-resistivity. 
         [0135]    Another example of main compression coding information and auxiliary compression coding information will be described with reference to  FIG. 27 . 
         [0136]    Here is considered a case of compression processing in which the unit of compressed blocks  900  is 32 horizontal pixels and that of sub-compressed blocks  901 ,  902 ,  903  and  904  is 8 pixels. 
         [0137]    A first compressor (compressor A 133 ) processes first compression of the sub-compressed blocks  901 ,  902 ,  903  and  904  in sub-compressed block units, and auxiliary compression coding information sets (first compression coding information sets  905 ,  906 ,  907  and  908 ) in sub-compressed block units and compressed image data sets (first compressed image data sets  909 ,  910 ,  911  and  912 ). A second compressor (compressor B 134 ) further processes second compression of four inputted compressed image data sets (first compressed image data  909 ,  910 ,  911  and  912 ) in sub-compressed block units, and generates one each of main compression coding information set (second compression coding information set  914 ), compressed image data set (second compressed image data set  914 ) and compressed image data set (second compressed image data set  915 ). By transmitting the main compression coding information over a transmission path higher in error resistivity than the transmission path for the auxiliary compression coding information sets (first compression coding information sets  905 ,  906 ,  907  and  908 ) and the compressed image data set (second compressed image data set  915 ), expansion can be processed even in sub-compressed block units on the transmission path higher in transmission error rate, and the range affected by errors can be restrained to the range of sub-compressed blocks. 
         [0138]    Error resistivity can be further enhanced by transmitting a common compression coding information set  913  for the first compression coding information sets  905 ,  906 ,  907  and  908  as main compression coding information in addition to the second compression coding information  914 . 
         [0139]    As another instance of compression coding information, here is considered compression processing in which, for instance, the compressed block unit is 32 horizontal pixels and the sub-compressed block unit is 8 pixels, and size information is added in sub-compressed block units. The overall total of size information sets in sub-compressed block unit, namely size information on compressed block unit is included in main compression coding information, and size information is included in auxiliary compression coding information in sub-compressed block unit. By transmitting the main compression coding information over a transmission path higher in error resistivity, if an error arises in the auxiliary compression coding information on a transmission path higher in transmission error rate, the error can be prevented from affecting the next compressed block by generating the size of compressed block units on the basis of the main image coding information and skipping expansion processing equivalently to that size. 
         [0140]    If there is a surplus capacity for data transmission on a transmission path higher in error resistivity, the whole size information on individual sub-compressed blocks may as well be transmitted as main compression coding information. In this case, if an error arises in auxiliary compression coding information, the error can be prevented from affecting other sub-compressed blocks by generating the size of the sub-compressed block in which the error has occurred on the basis of the main image coding information and refraining from expansion processing equivalently to that size. 
         [0141]      FIG. 7  is a block diagram showing one example of the compression processor  114 . 
         [0142]    An input section  130  is an input section for inputting image data to the compression processor  114 . 
         [0143]    The inputted image data are supplied to a compressor A 133 , a compressor B 134  and a compressor C 135 . The compressor A 133 , compressor B 134  and compressor C 135  process compression of the inputted image data in different ways from one another, and generate compression coding information and compressed image data. To add, any other compressor than what is designated by a control signal  131  can be suspended from compression processing or the action clock itself can be stopped to save power consumption. 
         [0144]    Each of the compressor A 133 , compressor B 134  and compressor C 135  is configured of a compressing circuit that compresses a plurality of image data sets constituting a compressed block. One example of compression formula can be configured by operating Wavelet conversion in the horizontal direction and coding the result of the arithmetic operation. As the compression formula, Hadamard transform, run length encoding, Huffman encoding, differential encoding or the like may be applied. 
         [0145]    Further, as another example of compression formula, a compressing circuit that compresses a plurality of image data sets in the vertical direction. By one example of compression formula, first a difference is taken in the vertical direction for compressing a unit block of image data of two lines in the vertical direction and 16 pixels in the horizontal direction, and then a difference is taken in the horizontal direction. A compression formula of encoding the result can be used. 
         [0146]    One example of other compression formulas uses a circuit that, when chromatic difference signals of the 444 format or  422  format are inputted, curtails them into the 422 format or the 420 format. When the 444 format or the 422 format is inputted, if a prescribed compression rate is surpassed in the compression processor  114  shown in  FIG. 8  to be referenced afterwards, curtailment to the 422 format or the 420 format may be processed as well. 
         [0147]    The compression rate in this context means the ratio of the data quantity after compression to that before compression. If, for instance, the data quantity before compression is 100 and the data quantity after compression is 30, the compression rate is 30%. Therefore, the higher the compression rate, the greater the data quantity after compression, resulting in less deterioration of picture quality. 
         [0148]      FIG. 10  is a block diagram showing one example of configuration of the compressor A 133 . 
         [0149]    An input section  150  is an input section for inputting image data to the compressor A 133 . 
         [0150]    An input section  151  is an input section for inputting control signals for controlling the compressor A 133 . 
         [0151]    A first compressor  153  is a block that processes compression of inputted image data and generates compression coding information and compressed image data. The compression coding information generated by the first compressor  153  is supplied to the compressed code information generator  155 . Further, the compressed image data generated by the first compressor  153  are supplied to a selector  156 . 
         [0152]    The compressed code information generator  155  is a block that generates main compression coding information and auxiliary compression coding information from the inputted compression coding information. The compressed code information generator  155  may as well have a memory for temporarily storing the generated main compression coding information and auxiliary compression coding information. 
         [0153]    The selector  156  is a block that selects and outputs the compressed image data supplied from the first compressor  153  and the main compression coding information and auxiliary compression coding information data supplied from the compressed code information generator  155 . 
         [0154]      FIG. 11  is a block diagram showing one example of configuration of the compressor A 133 . 
         [0155]    An input section  160  is an input section for inputting image data to the compressor A 133 . 
         [0156]    An input section  161  is an input section for inputting control signals for controlling the compressor A 133 . 
         [0157]    A first compressor  163  is a block that processes first compression of inputted image data and generates auxiliary compression coding information and compressed image data. The auxiliary compression coding information generated by the compressor  163  is supplied to a selector  166 . Further, the compressed image data generated by the first compressor  163  are supplied to a second compressor  164 . 
         [0158]    The second compressor  164  is a block that processes second compression of inputted compressed image data and generates main compression coding information and compressed image data. The main compression coding information and compressed image data generated by the second compressor  164  are supplied to a selector  166 . 
         [0159]    The selector  166  is a block that selects and outputs auxiliary compression coding information supplied from the first compressor  163  and main compression coding information and compressed image data supplied from the second compressor  164 . 
         [0160]    The configuration of this example makes possible the processing of compression in two stages shown in  FIG. 27 . Further, though this example is a case of using two compressors, compressors may as well be provided for three or more stages. 
         [0161]    The outputs of the compressor A 133 , compressor B 134  and compressor C 135  are supplied to a selector  136 . 
         [0162]    Although the description of this case refers to a compression processor having three compressors  133 ,  134  and  135 , the number of compressors may as well be only one or two, or four or more. 
         [0163]    The selector  136  selects out of the compressor A 133 , compressor B 134  and compressor C 135  what satisfies a compression rate requirement and has a high picture quality index, and supplies it to an error correction code generator  137 . The picture quality index is an index whose value improves with a decrease in difference between, for instance, image data restored from compressed image data and image data before compression. The highest level is achieved no compression loss arises and reversible coding is accomplished. To simplify the calculation of the picture quality index, the value of the picture quality index may be prepared in advance for each different compression formula. It may be so defined that a higher picture quality index is achieved when reversible coding is accomplished after curtailment to the 422 format than when compression is done without changing from the 444 format to invite generation of compression loss. If compression rather results in an increased data quantity, a prescribed compression rate is achieved by opting for curtailment to the 422 format or the 420 format before compression or reducing the number of quantified bits, and a picture quality index is so set as to match the curtailment or the reduction in the number of quantized bits. 
         [0164]    Also, the operation of any one of the compressor A 133 , compressor B 134  and compressor C 135  may be validated with a control signal inputted from an input section  131 , with the two others suspended from operation. In this case, control information indicating the compressor whose operation is valid is inputted to the selector  136  from the input section  131 . The selector  136 , on the basis of the control information, outputs an output signal of the compressor whose operation is valid to the error correction code generator  137 . 
         [0165]    An error correction code generator  136  calculates an error correction code for each unit of image data compressed by the compressor C 135 , compressor A 133  and compressor B 134  (compressed image data), adds the code to the compressed image data, and outputs the image data units to a memory controller  139 . Available systems of error correction include the CRC (Cyclic Redundancy Check) system and the parity check system. 
         [0166]    Whether or not to add the error correction code may be determined according to the data transmission capacity. The reason is that, if the data transmission capacity of the cable is limited, adding the error correction code would involve curtailment of more pixels or tones of gradation and accordingly invite picture quality deterioration over the whole screen. If there is a surplus in transmission capacity, the error correction code may be added to the compressed image data to enhance error resistivity. Determination of whether or not to process error correction may be left to the receiving side by transmitting together metadata on whether or not error correction is added to compressed image data. Also, the error resistivity level may be varied by altering error correction processing according to the compression formula applied, or information indicating what error correction code has been added may as well be added as metadata. Or no error correction may be processed and input data may be outputted as they are. 
         [0167]    The memory controller  139  temporarily accumulates in a memory unit  140  compressed image data, main compression coding information and auxiliary compression coding information supplied from an error code generator  137 . It also reads the main compression coding information and the compressed image data out of the memory unit  140  and outputs them in the valid period  406 . Further, it reads the main compression coding information out of the memory unit  140 , and outputs it in the horizontal blanking period  404  immediately preceding the valid period  406  in which the compressed image data are outputted. By another formula, any of compressed image data, main compression coding information and auxiliary compression coding information with an error correction code for one line may be transmitted in the valid period  406  for one line thereby to increase the transmission quantity. Also, the reliability of error correction may be enhanced by containing the error correction code in the main compression coding information and outputting the information in the horizontal blanking period  404 . 
         [0168]    An output section  132  outputs compressed image data, main compression coding information and auxiliary compression coding information from the memory controller  139 . Though not shown, operations of the blocks in  FIG. 7  are controlled in accordance with control signals from the controller  110  shown in  FIG. 1 . 
         [0169]      FIG. 12  is a block diagram showing one example of configuration of the error correction code generator  136 . To the input section  170 , compressed image data is inputted. The compressed image data is inputted to a holding unit  175  and an error correction code calculator  173 . The error correction code calculator  173  subjects the inputted compressed image data to a cyclic operation using a generating polynomial. 
       Examples of Generating Polynomial Include: 
       [0170]        G ( X )= X   16   ×X   12   ×X   5 +1  (Mathematical expression 1)
 
         [0000]    This generating polynomial gives a cyclic operation taking an exclusive OR of the bits in the inputted compressed image data. The unit of the operation shall be the unit of the compressed image data. 
         [0171]    An input section  171 , to which a signal indicating the period during which compressed image data is entered is inputted, supplies this signal to a timing generator  174 . The timing generator  174  outputs a signal indicating that a unit block equivalent of image data to count and compress the valid period of the compressed image data has been processed to the data holding unit  175  as an error correction calculation result output timing signal. Further, the timing generator  174  outputs together to the data holding unit  175  a timing signal indicating the input period of compressed image data and a timing signal indicating the compressed image data and the results of calculating the error correction code. 
         [0172]    The data holding unit  175  temporarily stores, in accordance with the timing indicated by the timing generator  174 , the results of calculation by the error correction code calculator  173  and the compressed image data into, for instance, a memory, flip-flop, delay element or the like, and successively outputs them to the output section  132 . 
         [0173]      FIG. 13  is a block diagram showing one example of configuration of the data transmission section  115 . 
         [0174]    An input section  180  outputs compressed image data to a serializer  184 . Further, an input section  181 , to which the clock of image data is inputted, outputs it to a PLL  186  and an output section  182 . 
         [0175]    As the clock of image data, a clock synchronized with the pixel clock used in the standard timing format of uncompressed image data is used. For instance, a clock obtained by half division of the pixel clock of uncompressed image data is used. In this case, as the clock will be 1/2 and the number of quantized bits will be 8/12 if the uncompressed image data are 12-bit quantized image data, the aforementioned prescribed compression rate should be set 1/3 or less. The clock may be 3/4 multiplied or 2/3 multiplied instead of being half divided. Using the clock synchronized with the pixel clock of uncompressed image data for transmitting the compressed image data provides the advantage that the receiving side, when restoring the uncompressed image data, can minimize the jittering of restored data by using a clock resulting from 4/2, 4/3 or 3/2 multiplication of the transmission clock as the pixel clock. 
         [0176]    The PLL  186  generates a clock or clocks by multiplying or dividing the inputted clock. Examples of multiplication include fivefold or tenfold multiplication of the frequency of the inputted clock. Either only one type of clock or two types of clock may be chosen for the clock generated by the PLL  186 . One example of one type of clock is a tenfold-multiplied product of the inputted clock. Examples two types of clock included a first clock speed giving priority to the data transmission quantity and a second clock speed slower than the first clock speed to give priority to reducing the frequency of error occurrence. Examples of speed include the first clock speed of tenfold-multiplied product of the input clock and the second clock speed of fivefold-multiplied product of the input clock. 
         [0177]    The multiplied clock or clocks generated by the PLL  186  are outputted to the serializer  184 . 
         [0178]    The serializer  184  serializes the compressed image data of the inputted YCbCr luminance chromatic difference signals bit by bit with a tenfold-multiplied clock, and outputs the serialized data to a level converter  185 . When there are 8 bits of data to be inputted to the input section  180  per clock inputted to the input section  181 , the TMDS transmission method, for instance, may be used by which DC components of a bit stream resulting from mapping and serializing the eight-bit data are suppressed. Where there are three cables to be connected to an output section  176 , 24 bits of compressed image data per input clock can be transmitted by serializing the data for each individual cable. 
         [0179]    The level converter  185  outputs signals of a form suitable for cable transmission via the output section  182 . 
         [0180]      FIG. 8  is a block diagram showing another example of configuration of the compression processor  114 . 
         [0181]    A memory controller  142  temporarily accumulates in the memory unit  140  compressed image data, main compression coding information and auxiliary compression coding information supplied from the error code generator  137 . It also reads auxiliary compression coding information and compressed image data out of the memory unit  140 , and outputs them in the valid period  406 . It further reads main compression coding information out of the memory unit  140 , and outputs it in the horizontal blanking period  404  immediately preceding the valid period  406  in which compressed image data are outputted. Further, it can read compressed image data out of the memory unit  140  and supply them to a selector  141 . 
         [0182]    The selector  141  is a block that selects either image data inputted from the input section  130  or compressed image data  143  supplied from the memory controller  142  and supplies what it has selected to the compressor A 133 , compressor B 134  and compressor C 135 . It may as well output the image data inputted from the input section  130  to a prescribed compressor and at the same time output the compressed image data  143  to some other compressor. The configuration of this example makes possible two-stage compression processing shown in  FIG. 27 . Compression in three or more stages may also be processed. 
         [0183]      FIG. 9  is a block diagram showing still another example of configuration of the compression processor  114 . 
         [0184]    A selector  138  outputs to a memory controller  145  main compression coding information and auxiliary compression coding information supplied from the error code generator  137 , and outputs to a selector  144  compressed image data supplied from the error code generator  137 . 
         [0185]    The memory controller  145  temporarily accumulates in the memory unit  140  main compression coding information and auxiliary compression coding information supplied from the selector  138 . It also reads auxiliary compression coding information out of the memory unit  140 , and outputs it in the valid period  406 , to be described afterwards, via the selector  144 . It further reads main compression coding information out of the memory unit  140 , and outputs it via the selector  144  in the horizontal blanking period  404  immediately preceding the valid period  406  in which it outputs auxiliary compression coding information. 
         [0186]    The selector  144  is a block that selects compressed image data supplied from the selector  138  and main compression coding information and auxiliary compression coding information data supplied from the memory controller  145 , and outputs them to the output section  132 . 
         [0187]    In this example, the selector  138  may output auxiliary compression coding information, together with compressed image data, directly to the selector  144  without going via the memory controller  145 . In this case, the memory controller  145  processes reading and writing of main compression coding information out of and into a memory. By choosing the configuration of this example, the memory capacity of the memory unit  140  on the transmitter  100  side can be kept small. 
         [0188]      FIG. 14  through  FIG. 17  show an example of packet for transmitting some of main compression coding information. 
         [0189]      FIG. 14  and  FIG. 16  show an example of packet header, which a common header type 0Bh, indicating that this is information regarding the compression coding formula according to the invention, is stated in the first header block HB0. Each bit of HB1 and bits 4 through 7 of HB2 are 0 for future expansion. Eco_Packet# shown in bits 0 through 3 of HB2 indicates identification in the frame.  FIG. 15  and  FIG. 17  show an example of data of 28 bytes transmitted following the header. 
         [0190]    In the header of  FIG. 14 , 0h is allocated as Eco_Packet#, indicating that a packet configured of the header  FIG. 14  and the data of  FIG. 15  is common information (main compression coding information) among the frames. This packet is arranged in a vertical blanking period, and transmitted at least once for each image frame. The contents of the data of  FIG. 15  will be described below. 
         [0191]    Color_Sample denotes color sample information; for instance, 0 is a YCbCr luminance chromatic difference signal in the 444 format (hereinafter referred to as YCbCr444), 1, a YCbCr luminance chromatic difference signals in the 422 format (hereinafter referred to as YCbCr422), 2, a YCbCr luminance chromatic difference signals in the 420 format (hereinafter referred to as YCbCr420), 3, an RGB signal in the 444 format (hereinafter referred to as RGB444), and 4 through 7 for future expansion. To signals in the 422 format or the 420 format a bit indicating CbCr sample position information may as well be additionally allocated. 
         [0192]    Eco_Mem is 0 when a packet transmitting some of main compression coding information shown in  FIG. 16  and  FIG. 17  is to be described afterwards to be transmitted in the horizontal blanking period immediately preceding the valid period  406  in which compressed image data is transmitted, and 1 when it is to be transmitted in the horizontal blanking period immediately following the valid period  406  in which compressed image data is transmitted. 
         [0193]    CD denotes Color Depth; for instance, 4h is a 24-bit Color, a total of 8 bits of YCbCr components, 5h, a 30-bit Color, a total of 10 bits of YCbCr components, 6h, a 36-bit Color, a total of 12 bits of YCbCr components, 7h, a 48-bit Color, a total of 16 bits of YCbCr components, and the rest for future expansion. This definition conforms to the HDMI-prescribed Deep Color Mode definition. 
         [0194]    Eco_FLM is supposed to be 1 when the compression coding formulas of all blocks in the frame are the same, and 0 when the formula is to be set block by block. Where it is 1, the compression coding formulas of Y, Cb and Cr are respectively stated in Eco-CD0, Eco-CD1 and Eco-CD2 to be described afterwards. 
         [0195]    The ratio between CK_N and CK_M (CK_N/CMM) represents the frequency ratio between the pixel clock of uncompressed image data and the clock of the communication path for transmitting compressed data, for instance the TMDS clock. For instance, if CK_M=2 when CMN=1, the TMDS clock of the transmission system is 297 MHz, 1/2 of 594 MHz of the pixel clock of uncompressed image data at 4k2k. 
         [0196]    Eco_Block denotes the number of pixels constituting a compressed block. 
         [0197]    Eco_CD0 through Eco_CD3 denote four kinds of candidates for compression coding information to be applied to individual image data unit blocks. As in one example shown in  FIG. 18 , the four kinds are selected from compression coding information Eco_Code for units of image data to be compressed. 
         [0198]    One or more of packets, each including a header shown in  FIG. 16  and data shown in  FIG. 17 , are transmitted in each horizontal blanking period. Eco_Packet# in the header shown in  FIG. 16  denotes the serial number of the packet to be transmitted over each line, beginning with 1 and successively increased by 1 each time. 
         [0199]    Eco_length — 0 through Eco_length — 39 represent size information on compressed blocks transmitted in the valid period  406 . Examples of size information include the bit size and byte size of compressed blocks. It may as well be information on which the bit size and byte size of compressed blocks are based. For instance, there is a method by which, when a compressed block size S_Block takes on any value from 32 bits to 64 bits at two-bit intervals, the bit size of a compressed block is defined by the following equation. 
         [0000]        S _Block=32+(2× Eco _length_#)(# is 0  to  39)  (Mathematical expression 2)
 
         [0000]    In the example above, Eco_length# is four bits. 
         [0200]    Eco_length_# may be defined individually for each of Y, Cb and Cr, or by a value which is the total compressed block size of Y, Cb and Cr. In the latter, the transmission quantity of Eco_length_# can be reduced to 1/3. 
         [0201]    The compression coding information defined in compressed block units is transmitted as auxiliary compression coding information, together with compressed image data in the valid period  406 . Types of the auxiliary compression coding information include Eco_Error — 0 through 39 and Code — 0 through Code — 39. 
         [0202]    Eco_Error — 0 through Eco_Error — 39 represent an error coding formula. The error coding formula is an error correction coding formula in the error correction code generator  136  for calculation regarding data transmitted in the valid period  406 . Examples of error correction coding formula include the CRC (Cyclic Redundancy Check) formula and the parity check formula. 
         [0203]    Code — 0 through Code — 39 state numbers selected from four types of compression coding information stated by Eco_CD0 through Eco_CD3 of  FIG. 15  in the order of Y, Cb and Cr components in each image data unit block. For instance, if Code — 0 representing the compression coding information on the Y component in the first image data unit block is 1, Eco_CD1 is indicated. If Eco_CD1 indicates 10, it means data obtained by compressing the 444 format Y component of the original image data from  FIG. 18  by the differential coding formula. 
         [0204]    When the two vertical lines shown in  FIG. 4  are to constitute an image data unit block, Code — 0 on the first line indicates compression coding information on the image data unit block  503 , and Code — 0 on the second line indicates compression coding information on the image data unit block  504 . 
         [0205]    When Color_Sample in  FIG. 15  indicates the 444 format, Code — 1 denotes compression coding information on Cb of a first image data unit block, Code — 2 denotes compression coding information on Cr of the first image data unit, and Code — 3 denotes compression coding information on Y of a second image data unit block. When Color_Sample indicates the 420 format, Code — 1 denotes compression coding information on Y of the second image data unit block, Code — 2 denotes compression coding information on Cb (Cr on even-number lines) of the first and second image data units, and Code — 3 denotes compression coding information on Y of a third image data unit block. When Color_Sample indicates the 422 format, Code — 1 denotes compression coding information on Cb of the first and second image data unit blocks, Code — 2 denotes compression coding information on Y of the second image data unit, and Code — 3 denotes compression coding information on Cb of the first and second image data unit blocks. 
         [0206]    Further, when Code — 0 indicates 0, it denotes Eco_CD0, or when Eco_CD0 indicates 6, it means that, as seen from  FIG. 18 , the 444 format Y, Cb and Cr components 12-bit data of the original image are curtailed to 8 bits of the 420 format. As Code — 0 of only the Y component determines the transmission forms of Cb and Cr in this case, information of Code — 1 indicating the Cb component and that of Code — 2 indicating the Cr components are unnecessary, and 0 may be stated regarding them. 
         [0207]    Now, though not shown in  FIG. 1 , the image receiving device  200  is mounted with a ROM storing EDID (Enhanced Extended Display Identification Data) manifesting the performance features of the image receiving device  200 . Information to make possible determination of whether or not the image receiving device  200  is responsive to compression or expansion may be added into this ROM. This enables the image transmitting device  100  to read out of the ROM storing EDID of the image receiving device  200  information to determine whether or not it is responsive to compression or expansion and, if it is a responsive device, to transmit compressed image data or, if it is not a responsive device, to transmit the image in the usual size not compressed, thereby to keep compatibility also with an image receiving device not responsive to compression processing. Or if it is a device that reads out information to determine whether or not the device is responsive to an error correction coding formula for transmitting compression coding information in the valid period  406  and, if it is a responsive device, to process error correction coding and compression coding information or, if it is not a responsive device, to transmit the image in the usual size not compressed, thereby to keep compatibility also with an image receiving device not responsive to compression processing. Or if it is not a responsive device, resistivity to transmission errors may be enhanced by using the error correcting function of packets in the blanking period  407 . Also, the user may be notified by indicating on the display section  208  that the image receiving device is not responsive to compression, the image is in the usual size and there is no responsiveness error correction coding. 
         [0208]    An example of statement of this EDID is shown in  FIG. 19 .  FIG. 19  shows an example of expansion into what is known as an HDMI-VSDB area. 
         [0209]    At Bit 2 of Byte 6, an Eco_transfer flag is provided, which shows whether or not the device is responsive to the compressed coding transmission formula of this embodiment. As this area has been treated as a reserved area, it is stated as 0 in non-responsive legacy equipment, and only responsive equipment can maintain backward interchangeability by being stated as 1. Where this Eco_transfer flag is 1, statement of Byte 9 and Byte 10 is validated. 
         [0210]    Block — 64 and Block — 128 are flags indicate that the respective sizes of image data unit blocks to be compressed are 64 pixels and 128 pixels. The image data unit block size of 32 pixels is defined as a required mode in responding to this compressed image data transmission, and its statement is intentionally dispensed with for the sake of saving the EDID stating space. 
         [0211]    Eco-Codes 1 through 4 are flags indicating responsiveness to compressed coding formulas including the Wavelet conversion, run length encoding, Huffman encoding and differential encoding, whose respective examples are show in  FIG. 18 . 
         [0212]    CLK — 1, CLK3/4 and CLK1/2 are flags indicating responsiveness to modes in which the frequency of the TMDS transmission clock to 1/1, 3/4 and 1/2, respectively of the uncompressed image data clock. 
         [0213]    Eco_Errors 1 through 4 are flags which take on 1 to indicate responsiveness to respectively prescribed error coding formulas or 0 to indicate non-responsiveness. 
         [0214]    Eco_Mem takes on 1 when the main compression coding information is to be transmitted in the horizontal blanking period immediately preceding the valid period  406  in which compressed image data are to be transmitted, and takes on 2 when it is to be transmitted in the horizontal blanking period immediately following the valid period  406  in which compressed image data is to be transmitted. Numeral 3 indicates that it is responsive to both, and 0 indicates that it is responsive to neither. 
         [0215]    Or where the image transmitting device  100  is to be used as mobile equipment, since it has to be battery-driven, power consumption of the image transmitting device  100  becomes a factor to influence the length of time it can be continuously used. In this case, power consumption can be reduced by compressing image data for transmission and thereby reducing the data transmission quantity. This effect makes possible setting of a long continuously usable period by adding, for instance, a function such as a “power saving mode” as an operating mode of the image transmitting device  100  and uncompressed image data when power is supplied from outside or transmitting compressed image data when the equipment is battery-driven. 
         [0216]      FIG. 20  is a block diagram showing one example of configuration of the data reception processor  205 . 
         [0217]    An input section  220  outputs signals converted by a level converter  175  of the image transmitting device  100  to a level converter  22 . 
         [0218]    The level converter  224  converts signals converted in level by the image transmitting device  100  into digital signals, and outputs them to a deserializer  225 . One example of level conversion is conversion of differential signals to single-end signals. 
         [0219]    An input section  221  inputs a clock outputted from the image transmitting device  100  and outputs it to a PLL  226 . The PLL  226  generates a clock  10  times the inputted clock, and outputs it to the deserializer  225 . Further, the PLL  226  outputs from an output section  222  the pixel clock to be used in the image receiving device  200 . When the pixel clock of uncompressed image data of the original image is used in an image display device  200 , a clock resulting from (CK_M/CK_N) multiplication of the input clock by the PLL  226  on the basis of packet data in FIG.  13  is outputted from an output section  223 . 
         [0220]    The deserializer  225  parallelizes serialized data with a clock from the PLL  226  and outputs the parallelized data from the output section  222 . The deserializer  225  parallelizes data of a tenfold clock, turns them into eight-bit parallel data by prescribed TMDS decoding or the like, and outputs them from the output section  222 . 
         [0221]      FIG. 21  is a block diagram showing one example of configuration of the expansion processor  206 . Further,  FIG. 26  is an explanatory drawing of timing illustrating the processing concept of the expansion processor  206  regarding the compressed block shown in  FIG. 4 . An input section  230  is a data input section of the expansion processor  206 . Data inputted to the input section  230  includes HSYNC ( FIG. 26  ( a )) and VSYNC indicating sync signals of image data, compressed image data and auxiliary compression coding information sets  812  and  814  in the valid period  406 , and main compression coding information sets  811  and  813  in the horizontal blanking period  404 . To an input section  231 , the pixel clock of uncompressed image data after restoration, a compressed image data clock and the like are inputted. 
         [0222]    HSYNC, VSYNC, compressed image data clock and the pixel clock of uncompressed image data after restoration are supplied to a timing generator  236 . The timing generator  236  controls a counter with inputted HSYNC and VSYNC, and generates and outputs timings needed for the control of blocks in the expansion processor including timings for the vertical blanking period  401 , the vertical valid period  402 , the horizontal blanking period  404 , the horizontal valid period  405  and the valid period  406 . 
         [0223]    A compression coding information extractor  233  extracts compression coding information on each image data unit block sent in horizontal blanking periods, and stores it into a compression coding information memory  234 . 
         [0224]    The period of this storage is shown in  FIG. 26(   c ). Since the main compression coding information set  811  is data matching the compressed image data set  812  that follows, a period  815  of storing the information until the second-line main compression coding information  813  arrives is sufficient. However, where two lines of image data are vertically compressed for instance, at least compression coding information  816  for vertical expansion has to be held until the period of expand the second-line compressed image data. 
         [0225]    Compressed image data arriving within the horizontal valid period undergo correction of errors in the transmission system by an error corrector  235 . The error corrector  235  calculates for each unit of compressed image data the same error correction code as what the error correction code generator  137  does. The result of this calculation and an error correction code inputted from the compression coding information extractor  233  are compared and, if the result of comparison indicates any difference, error correction is processed. One example of error correction processing is CRC operation. Or, only error detection may be done, leaving interpolation for errors to be done in subsequent processing. 
         [0226]    The inputted compressed image data are supplied to an expander A 237 , an expander B 238  and an expander C 239 . 
         [0227]    The expander A 237 , expander B 238  and expander C 239  processes expansion of the compressed image data each in a different way on the basis of information in the compression coding information memory  234  to generate expanded image data, and outputs them to a selector  261 . 
         [0228]      FIGS. 26(   d ) and  26 ( e ) respectively show output data of each expander when the compressed blocks shown in FIG.  4  are processed for horizontal expansion by the expander A 237  and processed for vertical expansion by the expander B 238 . Horizontally expanded image data  818  and  819  represent the output data of the expander A 237 , and the vertically expanded image data  820  and  821  represent the output data of the expander B 237 . 
         [0229]    The selector  261  appropriately selects, on the basis of information in the compression coding information memory  234 , image data to be inputted to the input section  230 , the output of the expander A 237 , the output of the expander B 238  and the output of the expander C 239 , and outputs the selected data to an output section  232  as restored image data  824  ( FIG. 26(   f )). 
         [0230]      FIG. 25  is an explanatory drawing of timing illustrating the processing concept of the expansion processor  206  when the compressed block shown in  FIG. 3  is processed for horizontal expansion by the expander A 237 . 
         [0231]    The input section  230  is a data input section of the expansion processor  206 . The data sets inputted to the input section  230  include HSYNC ( FIG. 26(   a )) and VSYNC indicating sync signals of image data, compressed image data  802  and auxiliary compression coding information  804  in the valid period  406 , and main compression coding information sets  801  and  803  in the horizontal blanking period  404 . To the input section  231 , the pixel clock of uncompressed image data, compressed image data clock and the like after restoration are inputted. 
         [0232]    The compression coding information extractor  233  extracts compression coding information on each image data unit block arriving in a horizontal blanking period, and stores it into the compression coding information memory  234 . 
         [0233]    The period of that storage is shown in  FIG. 25(   c ). Since the main compression coding information  801  is a data set matching the compressed image data  802  that follows, a storage period  805  for the information until the arrival of the second line of the main compression coding information  803  will be long enough. 
         [0234]    The inputted compressed image data is horizontally expanded by the expander A 237  to generate horizontally expanded image data sets  806  and  807 , which are expanded image data and outputted to the selector  261  ( FIG. 25(   d )). 
         [0235]    The selector  261  appropriately selects, on the basis of information in the compression coding information memory  234 , image data to be inputted to the input section  230 , the output of the expander A 237 , the output of the expander B 238  and the output of the expander C 239 , and outputs the selected data to the output section  232  as restored image data sets  808  and  809  ( FIG. 25(   f )). 
         [0236]      FIG. 22  is a block diagram showing one example of configuration of the expansion processor  206 . This example is an expansion processor for which a formula of transmitting auxiliary compression coding information is transmitted, together with compressed image data in the valid period  406 , instead of in the horizontal blanking period  404 . 
         [0237]    When the data to be transmitted in the valid period  406  is not only compressed image data but also includes compression coding information, some compression formula may require a reduction of the compression rate of the compressed image data, and in such a case the picture quality of restored images may deteriorate substantially. To prevent this deterioration, the horizontal blanking period is shortened to a length just enough for transmission of two audio data transmission packets and the horizontal valid period can be extended correspondingly. When 4k2k image data of an uncompressed image is to be transmitted at a 297-MHz clock, half the 594 MHz of the pixel clock, it was 1920 for the horizontal valid period and 280 for the horizontal blanking period in Embodiment 1. For the transmission period of two audio packets, including guard bands before and after, 96 will be sufficient for the horizontal blanking period, and according the horizontal valid period can be extended by the remaining 184. There is an effect of permitting extension of 1920 of the horizontal valid period by about 95%. 
         [0238]    In this case, as the position and width of the horizontal sync signal deviates from the standard timing of the prescribed uncompressed image data, it is advisable to so restore, with reference to uncompressed image data SVDC (Short Video Descriptor) metadata assigned to the image data, the timing as to conform to the standard timing format on the receiving side. 
         [0239]    In  FIG. 22 , blocks having similar functions to their counterparts in  FIG. 21  are assigned respectively the same reference numbers. The difference is the addition of a second image coding information extractor  250  to the output section of an error correcting circuit  255 . 
         [0240]    In the example of  FIG. 21 , the compression coding information extractor  233  extracts compression coding information (packets in  FIG. 14  and  FIG. 15 ) in the vertical blanking period and compression coding information (packets in  FIG. 16  and  FIG. 17 ) in the horizontal blanking period. In this example, the compression coding information extractor  233  extracts only the main compression coding information to be transmitted in vertical blanking period or the horizontal blanking period, and stores it into the compression coding information memory  234 . 
         [0241]    In this example, instead of transmitting compression coding information in a packet processed for error correction in the blanking period, error correction similar to that for other compressed image data sets is processed. As a result, the main compression coding information processed for error correction by the error corrector  255  and outputted from the second compression coding information extractor  250  and the auxiliary compression coding information outputted from the compression coding information memory  234  are outputted to the expander A 237 , the expander B 238 , the expander C 239  and a selector  251 . 
         [0242]    In this example, since the compressed image data and the compression coding information are close to each other in timing, storage of compression coding information over one horizontal period is unnecessary except for common compression coding information within the frame, resulting in an effect of permitting a reduction in circuit dimensions. 
         [0243]      FIG. 23  is a block diagram showing another example of configuration of the expansion processor  206 . 
         [0244]    In  FIG. 23 , blocks having similar functions to their counterparts in  FIG. 21  are assigned respectively the same reference numbers. The difference is the addition of a selector  260  at a stage preceding the expanders. 
         [0245]    The selector  261  appropriately selects, on the basis of information in the compression coding information memory  234 , image data inputted to the input section  230  output, the output of the expander A 237 , the output of the expander B 238  and the output of the expander C 239 , and outputs the selected data to the output section  232 . The selector  261  can further select any of the output of the expander A 237 , the output of the expander B 238  and the output of the expander C 239 , and output the selected one to the selector  260 . By adopting the formula of this configuration, extension by two or more formulas can be processed for compressed image data inputted to the input section  230 . 
         [0246]    Though not shown, any of the output of the expander A 237 , the output of the expander B 238  and the output of the expander C 239  can be selected, and the selected one can be outputted to the compression coding information memory  234 . The use of this configuration enables, for instance, compressed auxiliary compression coding information  660  in  FIG. 5  to be processed for expansion. 
         [0247]      FIG. 24  is a block diagram showing still another example of configuration of the expansion processor  206 . In  FIG. 24 , blocks having similar functions to their counterparts in  FIG. 22  are assigned respectively the same reference numbers. The difference is the addition of a memory  270  at the stage following the input section  230 . 
         [0248]    A selector  271  has a function to output selected data the memory  270  in addition to the functions of the selector  251  shown in  FIG. 22 . The memory  270  is a block that temporarily stores main compression coding information, auxiliary compression coding information and compressed image data inputted from the input section  230  and expanded data supplied from the selector  271 , and supplies them to blocks of following stages. By using this configuration, expansion of data inputted to the input section  230  can be processed at a plurality of stages. If only one stage of expansion processing is needed, data supply from the selector  271  to the memory  270  can be dispensed with. 
         [0249]    The use of this configuration enables, for instance, expansion of image data compressed by the method shown in  FIG. 8  or  FIG. 11  to be processed. 
       Embodiment 2 
       [0250]    Another mode of realizing the image transmission device and the image receiving device described as Embodiment 1 will be described below. 
         [0251]      FIG. 29  shows one example of input and output waveforms of the serializer  184 . The serializer  184  serializes compressed image data corresponding to image data of inputted YCbCr luminance chromatic difference signals (hereinafter referred to as YCbCr image data) or image data of RGB signals (hereinafter referred to as RGB image data) with a tenfold multiplied clock into three one-bit data sets, and output them to the level converter  175 . 
         [0252]    In one example of serialization, image data of eight-bit YCbCr luminance chromatic difference signals or RGB signals is outputted in the order of MSB or LSB from the beginning with a tenfold multiplied clock. 
         [0253]    The level converter  185  outputs signals converted into a standard data transmission format via the output section  182 . Examples of standard data transmission format include a differential level signal form of the TMDS formula. In a blanking period of images in this form, since transmission of no image data is needed, strength against transmission errors is increased in transmitting data other than image data by using only four-bit parts of the data of the tenfold multiplied clock to be serialized by the serializer  184  and not using the remaining six bits. Further, by using the two kinds of clocks, clocks generated by the PLL  186  can be reduced to 1/2 of the clock for transmitting image data to obtain the same effect. 
         [0254]      FIG. 30  shows one example of data composition of the serializer  184 . There are three output lines of the serializer  184 , of which one is configured of sync signals (HSYNC and VSYNC), a packet head and fixed bits. The configuration is such that the remaining two lines are used for transmitting data. The packet size is a 32-cycle equivalent of the transmission clock. 
         [0255]      FIG. 31  shows one example of data composition of audio data superposed in a horizontal blanking period. In the audio packet, sub-packets are configured generating seven-byte data with the same bits for two lines of data to be transmitted to the serializer and attaching an error correcting code, such as a parity check, to the data. A packet for the horizontal blanking period is configured in a format of four lines of the sub-packets and four bytes of a packet header. 
         [0256]    As this configuration includes an error correcting code for sub-packet data, an error occurring on the transmission path can be corrected to increase error resistivity. Further, as data for transmitting sub-packet data are configured in a zigzag form on two physically different channels, an error arising in a burst-like way does not affect the other channel, data error can be corrected. The error correction rate is high enough for an improving effect of 10 −14  in the horizontal blanking period against 10 −9  in the horizontal valid period. 
         [0257]    It is advisable to transmit the error correction code of compressed images as the highly error-resistive packet. The following description will take up as an example of number of transmittable packets a case in which the number of pixels in the horizontal period is 2200 and that of pixels in the horizontal valid period is 1920. To add, the example of image form is YCbCr422. 
         [0258]    Assuming the size of images to be compressed to be 64 pixels (32 luminance pixels and 32 chromatic difference pixels), the size of 60 error correction codes (2-byte) will require 120 bytes. 
         [0259]    As the available capacity permits transmitting 28 bytes per packet, five packets will be a large enough size for the transmission. As the horizontal blanking period has 280 pixels, eight packets can be superposed. This configuration allows, even if a maximum of two packets are provided for audio packets as 192 kHz 8ch LPCM audio transmitting, transmission of a maximum of five packets of the error correction code in the horizontal period. 
         [0260]    When compressed image data of inputted RGB image data are to be outputted to the data transmission section  115  in compressed block units over respectively prescribed TMDS channels, periods in which no compressed image data are transmitted occurs between compressed blocks. Considered on a line-by-line basis, there is a problem that no substantial reduction of horizontal valid periods, compared with no compression is done. 
         [0261]      FIG. 32  shows one example of output waveforms on each of TMDS channel 0, TMDS channel 1 and TMDS channel 2 when compressed image data of inputted RGB image data is to be outputted to the data transmission section  115 . 
         [0262]    The following description concerns a case in which compression is processed for each of R, G and B components of RGB image data in this embodiment and R compressed image data, G compressed image data and B compressed image data are generated. CR0 and CR1 in the drawing are compressed image data in sub-compression blocks, and a compressed block is configured of CR0 and CR1. CR2 is the leading sub-block of the next compressed block. The same applies CG0, CG1, CG2, CB0, CB1 and CB2 as what applies to CR0, CR1 and CR2 mentioned above. 
         [0263]    In this embodiment, it is made possible to reduce the non-transmission period for compressed image data between compressed blocks and sub-compression blocks by transmitting R compressed image data clammed in bit units and transmitting them over TMDS channel 0. 
         [0264]      FIG. 35  shows another example of output waveforms on each of TMDS channel 0, TMDS channel 1 and TMDS channel 2 when compressed image data of inputted RGB image data is to be outputted to the data transmission section  115 . 
         [0265]    In this embodiment, where sub-compression blocks  1300 ,  1301 ,  1302 ,  1305 ,  1306 ,  1309  and  1310  cannot be divided into even numbers by 8 bits, the leading bit of any sub-compression block is caused to be positioned always as the leading bit of a channel by adding stuffing data sets  1303 ,  1304 ,  1307 ,  1308  and  1311  at the end. In this way, the receiving circuit for sub-compression blocks on the image receiving device side can be simplified. Although stuffing data is added in sub-compression block units in this example, the addition may as well be done in compressed block units as shown in  FIG. 36 . 
         [0266]    The examples of this embodiment described with reference to  FIG. 32  and  FIG. 35  involve a problem the transmission band occupied by transmitted compressed image data is limited to the TMDS channel on which the compressed data quantity is the greatest, entailing elongation of the valid period, because compressed image data corresponding to RGB image data inputted to the data transmission section  115  is outputted to respectively prescribed TMDS channels. 
         [0267]      FIG. 33  shows another example of output waveforms on each of TMDS channel 0, TMDS channel 1 and TMDS channel 2 when R compressed image data, G compressed image data and B compressed image data, which are components of compressed image data of inputted RGB image data, are to be outputted to the data transmission section  115 . 
         [0268]    In this embodiment, R compressed image data, G compressed image data and B compressed image data are successively outputted in this order in sub-compression block units to TMDS channel 0, TMDS channel 1 and TMDS channel 2 successively in an interleaved way. Here is taken up, by way of example, a case in which R compressed image data CR0 is in 18 bits, G compressed image data CG0 in 37 bits, B compressed image data CB0 in 8 bits, R compressed image data CR1 in 20 bits, G compressed image data CG1 in 18 bits and B compressed image data CB1 in 14 bits. 
         [0269]    As the use of the above-described output formula enables compressed image data corresponding to RGB image data inputted to the data transmission section  115  to be transmitted over the three TMDS channels in an evenly shared way, the valid periods for transmitting compressed image data can be shortened. Although outputting in this case is done in sub-compression block units in the order of RGB, it may as well be done in compressed block units as shown in  FIG. 34 . 
         [0270]      FIG. 37  shows still another example of output waveforms on each of TMDS channel 0, TMDS channel 1 and TMDS channel 2 when compressed image data of YCbCr444 image data to be inputted to the data transmission section  115  are to be outputted. The proportions of data quantities of the components of YCbCr444 image data are the same among Y image data, Cb image data and Cr image data. Incidentally, the proportions of data quantities of the components of YCbCr422 image data are 1 each for Cb image data and Cr image data against 2 of Y image data. 
         [0271]    Reference numeral  1500  denotes image data inputted to the compression processor  114 . Reference numerals  1501 ,  1502  and  1503  respectively denote Y compressed image data (luminance-compressed image data), Cb compressed image data (Cb chromatic difference-compressed image data) and Cr compressed image data (Cr chromatic difference-compressed image data), which are components of compressed image data generated by compression of Y image data, Cb image data and Cr image data. 
         [0272]    Because of the characteristic of human vision that is more sensitive to luminance (Y) components than to chromatic difference (Cb and Cr) components, it is possible to make the data quantity of compressed image data of Cb components (hereinafter referred to as Cb compressed image data) and the data quantity of compressed image data of Cr components (hereinafter referred to as Cr compressed image data) smaller than the data quantity of compressed image data of Y components (hereinafter referred to as Y compressed image data) by setting the compression rate of Y components higher than the compression rates of Cb components and Cr components. 
         [0273]    This embodiment represents one example of compression processing of image data higher in priority of transmission among different components of image data at a higher compression rate. 
         [0274]    More specifically, the level of priority of Y compressed image data higher in those of Cb compressed image data and Cr compressed image data and, as the width of output bit from the data transmission section  115 , 12 bits are allocated to Y compressed image data, 6 bits to Cb compressed image data, and 6 bits to Cr compressed image data. 
         [0275]    When Y compressed image data  1501 , Cb compressed image data  1502  and Cr compressed image data  1503  are to be outputted to TMDS channel 0 (8 bits/cycle), TMDS channel 1 (8 bits/cycle) and TMDS channel 2 (8 bits/cycle), respectively, the transmission bands occupied by the transmitted compressed image data is limited to the TMDS channel 0 on which the compressed data quantity is the greatest, entailing elongation of the valid period. 
         [0276]    Reference numerals  1505 ,  1506 ,  1507 ,  1508  and  1511  denote one example of output data where more channels (12 bits/cycle) are allocated to Y compressed image data than to Cb compressed image data (6 bits/cycle) and Cr compressed image data (6 bits/cycle). The use of this output formula enables the valid period for transmitting compressed image data to be shortened. 
         [0277]    To add, allocation of output bit width is instructed from the controller  110  to the data transmission section  115 . Or the data transmission section  115  may allocate in advance at predetermined rates of distribution according to an image format (for instance YCbCr444 or the like) instructed from the controller. The rates of distribution may be set by the controller  115 . 
         [0278]    Whereas this embodiment has been described with respect to a case in which the image data are YCbCr444, for other image signals such as RGB signal, too, the level of transmission priority may be given to each individual compressed image data set, and the bit width of outputting to an output transmission path (for instance TMDS channel 0, 1 or 2). For example where the image data is RGB signals, there is a method by which the level of transmission priority for G components can be set higher than for the levels of transmission priority for R components and B components. More specifically, there is a method by which 12 bits are allocated as bit width of outputting to G components, and 6 bits each are allocated as bit width of outputting to R components and B components. 
         [0279]    Further, as another case of the level of transmission priority in which the image data are YCbCr444, there is a method by which a level of transmission priority higher the other chromatic difference components is allocated to 4:2:2 components. More specifically, it is a method by which 20 bits are allocated as the output bit width for 4:2:2 and 4 bits each are allocated as the output bit width for the remaining Cb components and Cr components. 
         [0280]      FIG. 38  shows another example of output waveforms in which inputted Y compressed image data  1601  is outputted to the data transmission section  115 , and Cb compressed image data  1602  and Cr compressed image data  1603  are outputted to TMDS channel 0, TMDS channel 1 and TMDS channel 2. To add,  1600  denotes image data to be input to the compression processor  114 . 
         [0281]    Regarding this embodiment, a case in which bit 4, bit 5, bit 6 and bit 7 of TMDS channel 0 and bit 0, bit 1, bit 6 and bit 7 of TMDS channel 1 are lower in transmission error rate than other bits. 
         [0282]    Reference numerals  1604 ,  1605 ,  1606 ,  1607 ,  1608  and  1609  denote examples of output data where Y compressed image data is allocated to bits lower in transmission error rate on TMDS channel. The use of this output formula enables the error occurrence rate of Y compressed image data to be brought down. 
         [0283]    To add, in this embodiment Cb compressed image data is allocated to  1602 ,  1605  and  1607 , and Cr compressed image data is allocated to  1603  and  1609 . 
         [0284]    Further, information on the transmission error rate is supplied from the controller  110  to the data transmission section  115 . Or, on the basis of the transmission error rate, the controller may designate bit allocation of Y compressed image data, Cb compressed image data and Cr compressed image data to TMDS channels. Although YCbCr luminance chromatic difference signals have been taken up as an example in the description of this embodiment, in other image forms including RGB signals as well, a level of priority may be assigned to each compressed image data set in bit allocation to TMDS channels. 
         [0285]    Further, the level of transmission priority of each component may be represented by the compression rate of each component. In this case, a greater output bit width shall be allocated to components of a higher compression rate and a smaller output bit width shall be allocated to components of a lower compression rate. For instance, there is a method by which the compression rates of different components (Y, Cb and Cr) of YCbCr444 are respectively set to 80%, 40% and 40%, the levels of transmission priority are respectively set to 2, 1 and 1, or another method by which the output bit widths of different components (Y, Cb and Cr) are respectively set to 12 bits, 6 bits and 6 bits. 
       Embodiment 3 
       [0286]    Another mode of realizing the image transmission device and the image receiving device described as Embodiment 1 will be described below. 
         [0287]    In this embodiment, main compression coding information is transmitted in a packet area in the horizontal blanking period  406  shown in  FIG. 30 . It does not take on a packet structure in spite of using the packet area, and four-bit data are supposed to be transmitted on each channel. Further, auxiliary compression coding information  1740  is transmitted in the valid period. 
         [0288]      FIG. 39  shows one example of output data composition of the data transmission section  115  when main compression coding information  1700  is to be transmitted in the horizontal blanking period  406 . 
         [0289]    The use of this configuration can enhance error resistivity in transmitting the main compression coding information  1700  compared with transmitting in the valid period. However, transmitting over a transmission path of a high transmission error rate poses a problem of how to further enhance error resistivity. 
         [0290]      FIG. 40  shows one example in which main compression coding information  1710 , which is the same as the main compression coding information  1700 , is to be transmitted in a horizontal blanking period over the same transmission path. In this embodiment, the main compression coding information  1710  is outputted immediately after the main compression coding information  1700 . To add, the main compression coding information  1710  need not immediately follow the main compression coding information  1700 . The use of this configuration serves to enhance the redundancy of the main compression coding information, and makes it possible to provide main compression coding information with high transmission error resistivity even over a transmission path whose transmission error rate is high. To add, the redundancy level in this embodiment means the number of main compression coding information sets transmitted additionally. In this embodiment, the redundancy level is supposed to be 1. 
         [0291]      FIG. 41  shows one example in which main compression coding information  1720 , which is the same as the main compression coding information  1700 , is to be transmitted in a horizontal blanking period over a different transmission path. In this embodiment, a drop in transmission error resistivity due to transmission error rate fluctuations from channel to channel is restrained by transmitting the main compression coding information  1720  over a different channel than one for the main compression coding information  1700 . 
         [0292]    For instance, if the transmission error rate on channel 0 is higher than the transmission error rate on channel 1, allocation of redundant main compression coding information on channel 0 as shown in  FIG. 40  would invite a drop in error resistivity, but transmitting the same main compression coding information sets over a plurality of channels as shown in  FIG. 41  enables error occurrence rates of main compression coding information to be evened up. In this embodiment, two main compression coding information sets allocated to each channel, but they may as well be allocated to bit. For instance, there is a method to allocate the main compression coding information  1700  to bit 0 and bit 1 of channel 0 and bit 0 and bit 1 of channel 1 and allocate the main compression coding information  1700  to bit 2 and bit 3 of channel 0 and bit 2 and bit 3 of channel 1. Also, bit allocation may be changed in accordance with information on the transmission error rate. 
         [0293]      FIG. 42  shows an example in which the redundancy level is raised to 2 from the embodiments shown in  FIG. 40  and  FIG. 41 . The main compression coding information  1700  and main compression coding information  1730  and main compression coding information  1731 , both the same as the main compression coding information  1700 , are outputted. 
         [0294]    The resistivity of the transmission path to errors may as well be enhanced by raising the redundancy level of main compression coding information according to the transmission error rate. 
         [0295]      FIG. 43  shows a case in which the redundancy level is raised to 2 from the embodiments shown in  FIG. 40  and  FIG. 41 . The main compression coding information  1700  and main compression coding information  1730  and main compression coding information  1731 , both the same as the main compression coding information  1700 , are outputted. 
         [0296]    The redundancy level of main compression coding information may be raised according to the transmission error rate. 
         [0297]    Whereas transmitting of redundant main compression coding information when main compression coding information is to be transmitted in a horizontal blanking period has been described so far, where auxiliary compression coded images are to be transmitted in a valid period, the error resistivity of auxiliary compression coding information may as well be enhanced by transmitting redundant auxiliary compression coding information, which is the same as the auxiliary compression coding information, in a valid period. 
         [0298]      FIG. 43  shows one example of output data composition of the data transmission section  115  in a case in which, where auxiliary compression coding information is to be transmitted in a valid period, the redundancy level of the auxiliary compression coding information is set to 2. 
         [0299]    The use of this configuration can strengthen error resistivity when auxiliary compression coding information  1740  is to be transmitted. 
         [0300]    The redundancy level of main compression coding information may as well be raised according to the transmission error rate. 
       Embodiment 4 
       [0301]    In Embodiment 3, whereas the redundancy level of main compression coding information or auxiliary compression coding information is raised according to the transmission error rate, there is a problem that the transmission capacity of the transmission path over which additional redundant compression coding information is to be transmitted is limited. 
         [0302]    Therefore Embodiment 4 adopts a formula that allows an increase in the transmission capacity of the transmission path over which redundant compression coding information is to be transmitted by shortening the compression rate or the compression formula and lengthening or shortening the horizontal blanking period according to the transmission error rate. 
         [0303]    Instructions to increase/decrease the compression rate, compression formula and horizontal blanking period and information on the redundancy level of compression coding information are supplied from the controller  110  to the compression processor  114  and the data transmission section  115 . 
         [0304]    There is a method to convey by EIDI or CEC communication information on the situation of responses on the image receiving device side to instructions to increase/decrease the compression rate, compression formula and horizontal blanking period and to the redundancy level of compression coding information from the image receiving device to the image transmitting device. 
         [0305]    Decisions regarding instructions to increase/decrease the compression rate, compression formula and horizontal blanking period and the redundancy level of compression coding information in response to the transmission error rate may be made either by the controller  110  or individually by the compression processor  114  or the data transmission section  115 . 
         [0306]      FIG. 44  shows a case in which the transmission error rate is divided into three ranges and one example of compression rate, horizontal blanking period and redundancy level in each range. When a transmission error rate ER surpasses ERa (when the transmission error rate is high), the compression rate is set to 40%, the quantity of generated compressed image data is reduced, the horizontal blanking period is shortened, and the valid period is extended. The transmittable quantity of auxiliary compression coding information to be transmitted in the valid period can be thereby increased. In this embodiment, the resistivity of auxiliary compression coding information to transmission errors is enhanced by setting the redundancy level of auxiliary compression coding information to  2  and transmitting two sets of redundant auxiliary compression coding information of the same contents as the auxiliary compression coding information in the valid period. 
         [0307]    When the transmission error rate ER is at or below ERb (when the transmission error rate is low), images of high picture quality are made transmittable by setting the compression rate to 80% and increasing the quantity of generated compressed image data. The period in which no data are transmitted is increased by refraining from insertion of redundant compression coding information. The period in which no data is transmitted is the total of neither compressed image data nor auxiliary compression coding information is transmitted in the valid period  406  and neither packets nor main compression coding information is transmitted in the blanking period period  407 . Power saving is made possible by stopping the clock or taking actions at a frequency lower than the clock frequency in this non-transmission period. 
         [0308]    When the transmission error rate ER is above ERb but not above ERa (when the transmission error rate is normal), it is attempted not only to raise the transmission error resistivity but also to enhance the picture quality by setting the compression rate to 60% and the redundancy level of auxiliary compression coding information to 1. 
         [0309]      FIG. 45  shows a case in which the transmission error rate is divided into three ranges and another example of compression rate, horizontal blanking period and redundancy level in each range. When a transmission error rate ER surpasses ERa (when the transmission error rate is high), the compression rate is set to 40%, the quantity of generated compressed image data is reduced, the horizontal blanking period is extended, and the horizontal period is extended. The transmittable quantity of main compression coding information to be transmitted in the horizontal blanking period can be thereby increased. In this embodiment, the resistivity of auxiliary compression coding information and main compression coding information to transmission errors is enhanced by setting the redundancy level of auxiliary compression coding information to 1 and transmitting one set of redundant auxiliary compression coding information of the same contents as the auxiliary compression coding information in the valid period, setting the redundancy level of main compression coding information to 1, and transmitting one set of main compression coding information in the horizontal blanking period. 
         [0310]    In addition, the compression rate described with reference to  FIG. 44  and  FIG. 45 , the compression formula may as well be altered.  FIG. 46  shows a case in which the transmission error rate is divided into three ranges and one example of compression formula, horizontal blanking period and redundancy level in each range. The compression formula is changed over among formula A, formula B and formula C with the transmission error rate ER. When the transmission error rate ER is above Ra, resistivity to transmission errors can be enhanced by using a compression formula that involves less main compression coding information and can raise the redundancy level. Also, by applying a compression formula that can be expected to provide a high compression rate (for instance the compression rate of 40% in  FIG. 45 ), it is made possible to increase the transmittable quantity of auxiliary compression coding information or main compression coding information. 
         [0311]    Whereas the compression rate was taken up as an example in the description referring to  FIG. 44  and  FIG. 45 , and the compression formula was taken up in the description referring to  FIG. 46 , both the compression rate and the compression formula may as well be switched over according to the transmission error rate. 
         [0312]    Although this embodiment has been described with reference to a case in which redundant main compression coding information or redundant auxiliary compression coding information is outputted to enhance resistivity to transmission errors, the error coding formula may as well be switched over according to the transmission error rate. Or where the transmission error rate is high, in addition to reducing the quantity of compressed image data after compression as shown in  FIG. 45 , resistivity to transmission errors can be enhanced by extending the horizontal blanking period and transmitting part of the auxiliary compression coding information in the horizontal blanking period. 
         [0313]    With respect to this embodiment, a method to reduce compressed image data by processing compression at a low compression rate where the transmission error rate is higher than a prescribed level, a method to reduce compressed image data by processing compression by using a compression formula suitable for a low compression rate, a method to increase the transmission capacity of the transmission path for main compression coding information by extending the horizontal blanking period, or a method to increase the transmission capacity of the transmission path for auxiliary compression coding information by extending the valid period  406 , but a method to reduce the number of audio packets transmitted in the horizontal blanking period by audio data may be used as well. Examples of method to reduce audio data include a change from uncompressed audio form to compressed audio form and the number of audio channels from six to two. 
       Embodiment 5 
       [0314]    Whereas the compression rate, horizontal blanking period and redundancy level are increased according to the transmission error rate in Embodiment 4, there is a problem that picture quality and error resistivity in relation to the transmission error rate are determined irrespective of the type of contents of image data. In this embodiment, picture quality and transmission error resistivity suitable for the type of contents can be secured by altering the compression rate, horizontal blanking period and redundancy level according to the type of contents. To add, though the transmission error rate was not touched on in the description of this embodiment, this embodiment may further include switching over according to the transmission error rate. 
         [0315]      FIG. 47  shows one example of formula to switch over the compression rate, horizontal blanking period and redundancy level according to the type of contents. In this embodiment, where the contents are a cinematograph, the compression rate is set to 80%, the horizontal blanking period is extended, the redundancy level of main compression coding information is set to 2, and the redundancy level of auxiliary compression coding information is set to 1 to enhance the picture quality and error resistivity. On the other hand, where the contents are Japanese checker/Japanese chess, error resistivity is enhanced by shortening the horizontal blanking period, setting the redundancy level of main compression coding information to 1, and setting the redundancy level of auxiliary compression coding information to 1 while the compression rate is set to 40%, on account of the characteristic that there are many static parts. 
         [0316]    Of where the contents are sports, it is considered that visual sensitivity to errors is low though the images involve many moving parts and are difficult to compress, the horizontal blanking period is shortened and the redundancy level of both main compression coding information and auxiliary compression coding information is set to 0, namely no redundant compression coding information is inserted while setting the compression rate to 80%, thereby to increase non-transmission periods for data while seeking higher picture quality. 
       Embodiment 6 
       [0317]    In Embodiment 4, where the transmission error rate is below its prescribed level, picture quality enhancement was sought by increasing the quantity of compressed image data at a high compression rate. Regarding this embodiment, one example of method to enhance sound quality when the transmission error rate is below its prescribed level will be described with reference to  FIG. 48 . 
         [0318]    Reference numerals  1800  and  1802  denote the valid period  406  in which compressed image data or auxiliary compression coding information is transmitted, and  1801  denotes the blanking period  407  in which main compression coding information or audio packets audio packets are transmitted. Reference numeral  1810  denotes image data before compression. Reference numerals  1820 ,  1821  and  1822  concern one example in which main compression coding information  1820  and an audio packet  1821  are transmitted in a blanking period  1801  and auxiliary compression coding information or compressed image data  1822  are transmitted in a valid period  1802 . In this case, the number of audio packets transmittable within the blanking period  1801  is limited by the transmitted quantity of the main compression coding information  1820 . 
         [0319]    Here, when the transmission error rate is below its prescribed level, main compression coding information  1830  may also be transmitted in the valid period  1802 . In this case, high sound quality can be achieved by allocating more audio packets to the blanking period. 
         [0320]    Although error resistivity is higher in the blanking period than in the valid period, the transmittable data quantity is 1/3 or less if the transmission error rate is below its prescribed level. 
         [0321]      FIG. 49  shows another example of formula to realize high sound quality. Reference numerals  1910 ,  1911  and  1912  concern one example of transmitting main compression coding information  1910 , audio packet  1911 , auxiliary compression coding information and compressed image data  1912  when the valid period is not extended. In this example, there is no vacancy in which the main compression coding information  1910  can be transmitted in the valid period. 
         [0322]    Then, when the transmission error rate is below its prescribed level, a formula is chosen according to which the valid period is extended and main compression coding information  1921  is transmitted in this extended valid period  1902 . The main compression coding information  1921 , auxiliary compression coding information and compressed image data  1922  may be arranged anywhere if only it is within the extended valid period  1902 . In the case of this formula, since the transmittable data quantity in the valid period  1902  is three times that in the blanking period or even more, the extended length of the valid period is 3/1 or less of the transmission period of the main compression coding information in the blanking period. Therefore, as denoted by 1920, the blanking period in which audio packets can be transmitted can be extended. By increasing the audio data quantity, sound quality can be enhanced. Examples of sound quality enhancement features include an increased number of channels, audio signal generation at a higher sound frequency, audio signal generation with larger quantized bits, and relaxation of band limitations in high and low ranges. 
         [0323]    This embodiment so far described enables image data of a larger size than the currently prescribed image size to be transmitted over the currently prescribed transmission path by transmitting in a compressed form the image data to be transmitted by the image transmission device, and moreover it is possible to transmit compressed images having higher error resistivity by transmitting main compression coding information, which is part of compression coding information in an area made more error-resistive than the transmission area of image data. 
         [0324]    Also, when image data of the currently prescribed image size is to be transmitted, the data transmission quantity per prescribed length of time or the data transmission clock can be lowered, the frequency of error occurrence can be brought down and, moreover, a system highly reliable against errors on the transmission path can be architected. 
         [0325]    Further, a system that can deal with errors in such a manner that picture quality deterioration due to an error is kept from being conspicuous even if the error arises on the transmission path and the error cannot be perfectly corrected. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  . . . Image transmission device 
           101  . . . Input section 
           102  . . . Input section 
           103  . . . Input section 
           104  . . . Input section 
           105  . . . Tuner reception processor 
           106  . . . Network reception processor 
           107  . . . Recording medium controller 
           108  . . . Recording medium 
           109  . . . User IF 
           110  . . . Controller 
           111  . . . Stream controller 
           112  . . . Decoder section 
           113  . . . Display processor 
           114  . . . Compression processor 
           115  . . . Data transmission section 
           116  . . . Output section 
           191  . . . Data path 
           192  . . . Data path 
           193  . . . Data path 
           200  . . . Image receiving device 
           201  . . . Input section 
           202  . . . Input section 
           203  . . . User IF 
           204  . . . Controller 
           205  . . . Data reception processor 
           206  . . . Expansion processor 
           207  . . . Display processor 
           208  . . . Display section 
           300  . . . Cable