Abstract:
To obtain a high-quality still picture, the video reproducing apparatus comprises (i) a determining processor which determines whether or not a picture being reproduced as a still picture by a still picture reproducing processor is an intra-coded picture and (ii) a storing processor which stores coded data of a picture when it is determined that the picture being reproduced as a still picture by the still picture reproducing processor is the forward predictive-coded picture and stores difference data between the picture being reproduced and all the pictures referenced by the picture being reproduced as well as coded data of the intra-coded picture referenced by the picture being reproduced when the determining processor determines that the picture being reproduced as a still picture by the still picture reproducing processor is not the intra-coded picture.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to video reproducing apparatus capable of reproducing video based on compressed video data (for example, MPEG data).  
         [0003]     2. Description of the Prior Art  
         [0004]     MPEG (Moving Picture Experts Group), which is the international standard of the compression/expansion of color motion pictures, has been rapidly spread and applied to computers, communications, entertainment, etc. Of MPEG, MPEG 1 is employed in storage media such as a CD-ROM and MPEG 2 is employed in storage media such as a DVD and also in digital broadcasting.  
         [0005]     Now, referring to  FIG. 5 , the data arrangement structure (bit stream) of MPEG will be described. As shown in  FIG. 5 , the data arrangement structure of MPEG is formed in a hierarchy structure. The sequence  1  representing the entirety of one vide program is constituted by GOPs (Group of Picture)  2  each of which is an information block formed on a unit basis of a prescribed number of frames, and the GOP  2  is constituted by a prescribed number of pictures  3 . Further, the picture  3  is constituted by plural slices  4  which are blocks formed by dividing the picture  2 . The slice  4  is constituted by a plurality of macro blocks (hereinafter called as MBs)  5 . The MB  5  is constituted by blocks  6  each formed by 8×8 pixels. The MB  5  is a minimum unit for coding of MPEG, that is, DCT (Discrete Cosine Transform) processing.  
         [0006]     As shown in  FIG. 6 , GOP  2  includes an intra-coded picture (hereinafter called as an I picture) which is video information for intra-frame coding, a forward predictive-coded picture (hereinafter called as a P picture) which is video information for forward prediction coding, and a bidirectionally predictive-coded picture (hereinafter called as a B picture) which is video information for bidirectional prediction coding. As shown in  FIG. 6 , one GOP  2  is constituted by prescribed numbers of I, P and B pictures which are set in advance. In  FIG. 6 , as shown by the arrows, an I picture  7   a  and a P picture  7   e  are referenced by B pictures  7   b,    7   c,  and  7   d.  Further, the I picture  7   a  is referenced by the P picture  7   e.    
         [0007]     Further, compressed video data (MPEG data) before decoding is saved as coded data of the I picture with regard to the I picture, and as difference data between the P picture and the I picture referenced by the P picture or difference data between the B picture and the P picture. During the decoding, the P and B pictures are produced by using the coded data of the I picture and the difference data.  
         [0008]     In the reproduction mode, the respective I, P and B pictures shown in  FIG. 6  are sequentially reproduced. In this case, the compression rates of video information of these pictures differ from one another. In the still picture mode, when a picture stops at the B picture having the highest compression rate, the picture quality of this picture is quite degraded.  
         [0009]     There is an apparatus for reproducing the pictures of video data, wherein when the reproduction of video is paused in a prescribed manner at a B picture, one of I pictures closest to the B picture is displayed in place of the B picture (see, for example, Japanese Unexamined Patent Publication No. 2000-308016). There is also an apparatus for reproducing pictures of the video data wherein, when the reproduction of video is paused in a prescribed manner, a picture having the best picture quality among the pictures including a stopped picture and nearby pictures is displayed (see, for example, Japanese Unexamined Patent Publication No. 10-257501).  
         [0010]     However, according to the video reproducing apparatuses disclosed by Patent Documents 1 and 2, compressed video data is expanded (decoded) by pausing operation and still pictures based on the decoded video data are shown. Therefore, the picture quality of such a picture depends on a decoding function of the video reproducing apparatus. As a result, the picture quality of the still picture might be degraded.  
       SUMMARY OF THE INVENTION  
       [0011]     In view of the above, it is an object of the present invention to provide a video reproducing apparatus capable of obtaining a still picture with good picture quality which is not degraded compared with the original compressed video data.  
         [0012]     In order to achieve the above object, the present invention provides a video reproducing apparatus capable of outputting video signals based on video data constituted by a sequence of video information blocks each of which constitutes one unit by a prescribed number of intra-coded pictures each of which is video information for intra-frame coding and a prescribed number of predictive-coded pictures for prediction coding by motion compensation prediction, the video reproducing apparatus comprising: (i) a still picture reproducing processor reproducing one of the pictures as a still picture by motion compensation prediction when the reproduction of video signals is paused in a prescribed manner; (ii) a determining processor determining whether or not the picture being reproduced as a still picture by the still picture reproducing processor is the intra-coded picture; and (iii) a storing processor storing coded data of the picture when the above determining processor determines that the picture being reproduced as a still picture by the above still picture reproducing processor is the intra-coded picture, and storing difference data between the picture and all the pictures referenced by the picture as well as coded data of the intra-coded picture referenced by the picture when the above determining processor determines that the picture being reproduced as a still picture by the above still picture reproducing processor is not the intra-coded picture.  
         [0013]     As described above, according to the present invention, the above still picture reproducing processor reproduces one of the pictures as a still picture by motion compensation prediction when the reproduction of video signals is paused in a prescribed manner. Further, the above determining processor determines whether or not the picture being reproduced as a still picture by the above still picture reproducing processor is an intra-coded picture (I picture).  
         [0014]     The above storing processor stores coded data of the picture when the above determining processor determines that the picture being reproduced as a still picture by the above still picture reproducing processor is the intra-coded picture and stores difference data between the picture and all the pictures referenced by the picture as well as coded data of the intra-coded picture referenced by the picture when the above determining processor determines that the picture being reproduced as a still picture by the above still picture reproducing processor is not the above intra-coded picture (namely, the picture is a P picture or a B picture). When the picture being reproduced as a still picture is an I picture, coded data (intra-coded data) of the picture is captured as it is from the compressed video data and stored. Therefore, the picture quality is not degraded compared with the original compressed video data. Thus, by expanding the intra-coded data using a high-performance PC (Personal Computer) etc., it becomes possible to obtain a high-quality still picture. On the other hand, when the picture being reproduced as a still picture is a predictive coded picture (a P picture or a B picture), difference data between the predictive-coded picture and a picture to be referenced as well as the coded data of an I picture to be referenced by the predictive coded picture are captured as they are from the compressed video data and stored. Therefore, the picture quality is not degraded compared with the original compressed video data. Thus, by using a PC etc., it becomes possible to obtain a high-quality still picture based on such data.  
         [0015]     According to another aspect, the present invention provides a video reproducing apparatus capable of outputting video signals based on video data constituted by a sequence of video information blocks each of which constitutes one unit by a prescribed number of intra-coded pictures each of which is video information for intra-frame coding and a prescribed number of predictive coded pictures for prediction coding by motion compensation prediction, the video reproducing apparatus comprising: 
        a still picture reproducing processor reproducing one of the pictures as a still picture by motion compensation prediction when the reproduction of video signals is paused in a prescribed manner;     a determining processor determining whether or not the picture being reproduced as a still picture by the still picture reproducing processor is the intra-coded picture; and     a storing processor storing coded data of the picture when the determining processor determines that the picture being reproduced as a still picture by the above still picture reproducing processor is the intra-coded picture, and storing, with respect to all the pictures including the above picture belonging to the video information block, difference data between every two related pictures and coded data of the intra-coded picture when the above determining processor determines that the picture being reproduced as a still picture by the still picture reproducing processor is not the intra-coded picture.        
 
         [0019]     According to the present aspect with the above configuration, the still picture reproducing processor reproduces one of the pictures as a still picture by motion compensation prediction when the reproduction of the video signals is paused in a prescribed manner. Further, the above determining processor determines whether or not the picture being reproduced as a still picture by the above still picture reproducing processor is an intra-coded picture (I picture).  
         [0020]     Further, the above storing processor stores coded data of the picture when the above determining processor determines that the picture being reproduced as a still picture by the above still picture reproducing processor is the above intra-coded picture and stores, with respect to all the pictures including the picture belonging to the above video information block, difference data between every two related pictures and coded data of the intra-coded picture when the above determining processor determines that the picture being reproduced as a still picture by the still picture reproducing processor is not the intra-coded picture. When the picture being reproduced as a still picture is an I picture, coded data of the picture (intra-coded data) is captured as it is from the compressed video data and stored. Therefore, its picture quality is not degraded compared with the original compressed video data. Thus, by expanding the intra-coded data using a high-performance PC etc., it becomes possible to obtain a high-quality still picture. On the other hand, when the picture being reproduced as a still picture is a predictive coded picture (a P picture or a B picture), difference data and the coded data of the I picture are captured as they are from the compressed video data and stored. Therefore, the picture quality is not degraded compared with the original compressed video data. Thus, by using a high-performance PC etc., it becomes possible to obtain a high-quality still picture based on such data.  
         [0021]     According to another aspect, the present invention provides a video reproducing apparatus comprising a sending processor sending coded data saved by the above saving processor or coded data and the difference data saved by the above saving processor to an external memory.  
         [0022]     According to the present aspect with the above configuration, it is possible to save data stored by the above storing processor in an external memory such as a SmartMedia and a USB memory.  
         [0023]     According to still another aspect of the present invention, the above predictive-coded picture is a forward predictive-coded picture which is video information for forward prediction coding or a bidirectionally predictive-coded picture which is video information for bidirectional prediction coding.  
         [0024]     According to the present aspect with the above configuration, it is possible to capture coded data of the P picture or the B picture and difference data corresponding to such a picture from the compressed video data and store them. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a block diagram showing a configuration of a TV-broadcast receiving system;  
         [0026]      FIG. 2  is a flowchart showing main processing;  
         [0027]      FIG. 3  is a flowchart showing processing to store MPEG data which is called and performed in step S 150  of the flowchart shown in  FIG. 2 ;  
         [0028]      FIG. 4  is a flowchart showing another processing to store MPEG data which is called and performed in step S 150  of the flowchart shown in  FIG. 2 ;  
         [0029]      FIG. 5  is a conceptual diagram for showing a data arrangement structure of video data in MPEG; and  
         [0030]      FIG. 6  is a conceptual diagram for showing a configuration of GOP. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     Now, embodiments of the present invention will be described.  
         [0032]     Although the embodiments will be explained as to the case where the video reproducing apparatus of the present invention is a television tuner which is capable of outputting video signals based on digital broadcast signals. However, the video reproducing apparatus of the present invention is not limited to this, and it may be a DVD player etc. that can reproduce video images based on a DVD on which MPEG data is saved.  
         [0033]      FIG. 1  is a block diagram of a TV-broadcast receiving system comprising a TV tuner according to the present invention. In  FIG. 1 , the TV tuner  20  comprises a tuner unit  22  inputting frequency signals from an antenna  10 . The tuner unit  22  is of a so-called synthesizer tuner and, as channel-selection control signals, PLL data, namely, data of division ratio of a variable frequency divider in a PLL loop is given to the tuner unit  22 . Upon receipt of the PLL data as the channel-selection control signals from a CPU  28   a,  the tuner unit  22  selects one channel from a plurality of channels by extracting a frequency signal of a desired frequency band out of the inputted frequency signals. The CPU  28   a  detects a frequency offset of the tuner unit  22  and, based on the detected result, supplies an AFT voltage to the tuner unit  22 . Then, the tuner unit  22  corrects the frequency band to be extracted according to the AFT voltage so that an optimum channel selection can be made.  
         [0034]     The output from the tuner unit  22  is supplied to a digital reproduction unit  23 . Namely, the TV tuner  20  of the present embodiment is capable of reproducing digital broadcast. The digital reproduction unit  23  comprises a digital I/F  23   a,  a demodulator  23   b,  a descrambler  23   c,  a demultiplexer  23   d,  and an MPEG decoder  23   g.  The digital I/F  23   a  through which frequency signals are inputted from the tuner unit  22  comprises an A/D converter. Further, the demodulator to which signals are supplied from the digital I/F  23   a  comprises a channel equalizer and an error-correcting decoder, etc.  
         [0035]     Namely, the digital I/F  23   a  and the demodulator  23   b  convert the frequency signals inputted from the tuner unit  22  into digital signals and perform so-called ghost cancellation on digitally-demodulated signals based on the control information from the CPU  28   a.  Also, the digital I/F  23   a  and the demodulator  23   b  correct bit errors taking place on a transmission line, and obtain transport stream (TS) output. Further, in the above processing, the demodulator  23   b  detects the ratio of the bit errors to the whole data as a bit error rate.  
         [0036]     The transport stream obtained when the demodulator  23   b  performs demodulation and error correction is supplied to the descrambler  23   c.  Since the transport stream is usually scrambled, video and audio data cannot properly be reproduced as they are from it. Therefore, the descrambler  23   c  descrambles the transport stream so that the transport stream is restored to the data arrangement structure that can be reproduced. The transport stream descrambled is in a format where video signals, audio signals, and character information, etc. are multiplexed. Then, such data is supplied to the demultiplexer  23   d,  and the demultiplexer  23   d  demultiplexes the inputted data. Namely, the multiplexed data is demultiplexed. Further, it is possible for the descrambler  23   c  and the demutiplexer  23   d  to use DRAM  23   e  as a work area when they perform respective processing.  
         [0037]     When the demultiplexing is performed, the data is divided into MPEG data in which video signals and audio signals are compressed by a prescribed method, and data other than the video signals and audio signals such as character information about programs. The latter is supplied to the CPU  28   a.  On the other hand, the former is supplied to the MPEG decoder  23   g  and decompressed, namely, MPEG-decoded by the MPEG decoder  23   g.  Digital video signals and digital audio signals are produced by decoding the MPEG data, and the produced digital video signals are further converted into analog video signals.  
         [0038]     The MPEG decoder  23   g  comprises an OSD processing unit  23   h  that can display a prescribed still picture overlaid on a video image or replace the prescribed still picture with another and display it. The OSD processing unit  23   h  is capable of inputting the received data such as character information through the CPU  28   a  and producing a still picture based on the data such as the character information.  
         [0039]     The MPEG decoder  23   g  performs the MPEG decoding and OSD processing by using the DRAM  23   f  as an work area. Namely, the MPEG decoder  23   g  once writes the video data into the external DRAM  23   f  and performs the processing. In the DRAM  23   f,  MPEG data  23   f   1  demultiplexed by the demultiplexer  23   d  and pictures  23   f   2  such as an I picture, a P picture, and a B picture produced through the decoding by the MPEG decoder  23   g  are stored in sequence. When the reproduction of video based on digital broadcasting is paused in a prescribed manner, a still picture based on the picture  23   f  is reproduced in timing for it. Video signals decompressed and analog-converted by the MPEG decoder  23   g  are supplied to the video outputting unit  26 , which outputs the video signals to the television  30 . Various kinds of methods such as composite output and S-Video output can be adopted for outputting analog video signals to the television  30 .  
         [0040]     On the other hand, the audio signals produced by the MPEG decoding is inputted to a D/A converter  25  and is converted to analog audio signals by the D/A converter  25 . These analog audio signals are inputted to an audio outputting unit  27  and are outputted to the television  30  by the audio outputting unit  27 . However, if the television  30  is provided with an optical input terminal etc. and can accept digital audio signals, the digital audio signals may be outputted not through the D/A converter  25  but directly to the television  30 .  
         [0041]     The CPU  28   a  described earlier is connected to a bus  29  and, using a RAM  28   b  connected to the bus  29  as a work area, exercises control to achieve various functions of the television tuner  20 . A program for exercising control is stored in a ROM  28   c  in advance, and the CPU  28   a  exercises control while reading a prescribed program from the ROM  28   c  into the RAM  28   b  as required. The bus  29  is provided with a rewritable EEPROM  28   d,  and the CPU  28   a  exercises control using various kinds of data saved in the EEPROM  28   d.    
         [0042]     Channel-selection data  28   d   1  is saved in the EEPROM  28   d.  The channel-selection data  28   d   1  is for the tuner unit  22  to select a frequency band to be received based on a channel-selecting instruction from a remote controller  40  etc. Further, OSD data  28   d   2  is saved in the EEPROM  28   d  so that the OSD processing unit can perform OSD processing.  
         [0043]     Further, MPEG data  28   d   3  is saved in the EEPROM  28   d.  The MPEG data  28   d   3  is the one retrieved, while the reproduction of video is paused to reproduce a still picture, from the DRAM  23   f  and stored in the EEPROM  28   d  according to a prescribed instruction by the remote controller  40  etc., and corresponds to the still picture being reproduced. How the MPEG data is stored will be described later in detail.  
         [0044]     The bus  29  is connected with a remote control I/F  28   e  through which infrared blinking signals outputted from the remote controller  40  as an external device can be inputted. The infrared blinking signals are transmitted through the bus  29  to the CPU  28   a,  which exercises corresponding control. Further, the bus  29  is connected with a bus I/F  28   f  for connection to external devices through cables. Further, the bus  29  is connected with a USB I/F  28   g,  which enables data to be saved in a USB memory  28   h  as an external memory. The TV tuner  20  of the present embodiment is capable of sending the MPEG data  28   d   3  stored in the EEPROM  28   d  to the USB memory  28   h  based on a prescribed operation by the remote controller  40  etc.  
         [0045]     Now, referring to the flowchart of  FIG. 2 , a flow of main processing performed at the TV tuner  20  of  FIG. 1  will be described. First, in step S 100 , initial settings are made. In this step, processing related to the initial settings such as clearing the register of the CPU  28   a  and the RAM  28   b,  reading the set data for adjusting white balance from the EEPROM  28   d,  etc. are performed.  
         [0046]     Next, in step S 110 , processing to control video signals is performed. In this step, based on a current channel number saved in the EEPROM  28   d,  the CPU  28   a  controls, under its initiative, units and circuits making up the TV tuner  20  and performs processing for showing a television picture corresponding to the channel number on the television  30 .  
         [0047]     In step S 120 , it is checked whether or not an instruction to change the channel is given. Namely, it is checked whether or not an input to change the channel by the remote controller  40  etc. is made. When an instruction to change the channel is given, a frequency band corresponding to the channel instructed is determined in step S 130 . Then, processing to change the channel is performed by giving PLL data corresponding to the frequency to the tuner unit  22 .  
         [0048]     When performing processing of step S 130  or when it is determined that there has been no instruction to change the channel in step S 120 , it is checked in step S 140  whether or not the reproduction is paused. In this step, it is checked whether or not an input of instruction to pause the reproduction of video based on the digital broadcast signals is given by the remote controller  40  etc. When the reproduction has been paused, the MPEG data is stored in step S 150 . How the MPEG data is stored will be described in detail by referring to the drawing ( FIG. 3 ) later.  
         [0049]     When the processing in step S 150  is performed or when it is determined that the reproduction is not paused in step S 140 , it is checked whether or not an instruction to turn off the TV tuner  20  is given in step S 160 . When an instruction to turn off the TV tuner  20  has not been given, the process returns to step S 110 . When such an instruction has been given, the main processing is ended.  
         [0050]     Now, referring to  FIG. 3 , a flow of storing the MPEG data called and executed in step S 150  of the flowchart shown in  FIG. 2  will be described. First, in step S 200 , a still picture is reproduced. In this step, a still picture is reproduced in timing for pausing the reproduction of video signals in step S 140  of the flowchart shown in  FIG. 2 .  
         [0051]     Next, in step S 210 , it is checked whether or not an instruction to store the MPEG data is given. In this step, it is checked whether or not an instruction to store MPEG data corresponding to the still picture being reproduced in step S 200  is given by the remote controller  40  etc. If an instruction to store the MPEG data has not been given, the processing to store MPEG data is ended.  
         [0052]     On the other hand, in step S 210 , when it is determined that an instruction to store the MPEG data has been given, it is checked whether or not the reproduction is paused at an I Picture in step S 220 . Namely, it is checked whether or not the picture being reproduced is the one based on the I picture. If it is determined that the reproduction has paused at the I picture, coded data of the I picture is stored in step S 230 . In this step, the coded data of the I picture corresponding to the still picture being reproduced is retrieved from the DRAM  23   f  and stored in the EEPROM  28   d.  For example, in  FIG. 6 , when the I picture corresponding to the still picture is an I picture  7   a,  coded data of the I picture  7   a  is captured from the MPEG data saved in the DRAM  23   f  and stored in the EEPROM  28   d.    
         [0053]     On the other hand, in step S 220 , when it is determined that the reproduction has not been paused at the I picture (but a P picture or a B picture), processing is performed, in step S 240 , to retrieve coded data of the I picture referenced by the P picture or the B picture corresponding to the still picture being reproduced and difference data between the picture being reproduced and the I picture or the P picture to be referenced from the DRAM  23   f  and store them in the EEPROM  28   d.  For example, in  FIG. 6 , when the P picture corresponding to the still picture is a P picture  7   e,  of the MPEG data saved in the DRAM  23   f , coded data of the I picture  7   a  referenced by the P picture  7   e  and difference data between the picture being reproduced and the I picture  7   a  or the P picture  7   e  are captured and stored in the EEPROM  28   d.  Also, in  FIG. 6 , when the B picture corresponding to the still picture is a B picture  7   c,  of the MPEG data saved in the DRAM  23   f,  coded data of the I picture  7   a  referenced by the B picture  7   c,  difference data between the picture being reproduced and the I picture  7   a  or the B picture  7   c,  and difference data between the picture being reproduced and the P picture  7   e  referenced by the B picture  7   c  or the B picture  7   c  are captured and stored in the EEPROM  28   d.    
         [0054]     When the processing of step S 230  or step S 240  has been performed, it is checked whether or not an instruction to send the MPEG data is given in step S 250 . In this step, it is checked whether or not an instruction is given to send MPEG data stored in the EEPROM  28   d  in step S 230  or step S 240  to the USB memory  28   h.  If it is determined in step S 250  that the instruction to send the MPEG data has been given, the MPEG data stored in the EEPROM  28   d  is sent to the USB memory  28   h  in step S 260 . Also, when it is determined that an instruction to send the MPEG data has not been given, the processing to store MPEG data is ended.  
         [0055]     Now, a specific example of the main processing shown in  FIG. 2  will be described. First, processing related to initial settings is performed (step S 100 ) and a television picture corresponding to a currently received channel is displayed on the television  30  (step S 110 ). Then, it is checked whether or not an instruction to change the channel while the television picture is shown is given (step S 120 ). If it is determined that such an instruction has been given, the currently chosen channel is changed (step S 130 ). Further, it is checked whether or not the reproduction of video signals is paused while the television picture is shown (step S 140 ). If it is determined that the reproduction has been paused, processing to store MPEG data is performed (step S 150 ).  
         [0056]     When storing the MPEG data, first, a still picture is reproduced in timing for pausing the reproduction of video (step S 200 ). Then, it is checked whether or not an instruction to store the MPEG data is given during the reproduction of the still picture (step S 210 ). If it is determined that the instruction has been given, it is checked whether or not the still picture being reproduced is based on an I picture (step S 220 ). If it is determined that the still picture being reproduced is based on the I picture, coded data of the I picture is captured and stored in the EEPROM  28   d  (step S 230 ). Further, if it is determined that the still picture being reproduced is based on a P picture or a B picture, coded data of the I picture to be referenced and difference data are captured and stored in the EEPROM  28   d  (step S 240 ). Then, it is checked whether or not an instruction to send the stored MPEG data to the USB memory  28   h  is given (step S 250 ). If such an instruction has been given, the MPEG data is sent to the USB memory  28   h.    
         [0057]     In  FIG. 3 , the case is described in which, when the picture corresponding to the still picture being reproduced is a P picture or a B picture, in step S 240 , coded data of the I picture to be referenced by the picture and difference data between the picture and a picture to be referenced by the picture are stored in the EEPROM  28   d.  According to the present invention, however, as shown in  FIG. 4 , when the picture corresponding to the still picture being reproduced is a P picture or a B picture, with respect to all the pictures of GOP 2  including such a picture, difference data between every two related pictures and coded data of the I picture included in the GOP  2  may be stored in the EEPROM  28   d  in step S 340 .  
         [0058]     As has been described, according to the present invention, it is possible to provide a video reproducing apparatus capable of obtaining a high-quality still picture which is not degraded compared with the original compressed video data.