Abstract:
A sharp/blurred frame mode classifying unit specifies a frame to be subjected to sharp or blurred process. A 3D video signal extracting unit extracts a predetermined area or predetermined macro block in the specified target frame, and a 3D FFT  15  frequency-converts it to acquire a coefficient string. An intersection coordinate calculating unit finds a non-perceptible high frequency coefficient based on a spatio-temporal visual property model for the coefficient string, and a coefficient cut processing unit cuts the non-perceptible high frequency coefficient for a frequency conversion coefficient of orthogonal conversion of a predictive error signal. The code amount of a video signal is largely reduced for a high frame rate video by the processings only at the encode side without deteriorating the picture quality.

Description:
[0001]    The present application is claims priority of Japanese Patent Application Serial No. 2010-192719, filed Aug. 30, 2010, the content of which is hereby incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a code amount reducing apparatus, an encoder and a decoder in an apparatus for encoding video signals having a high frame rate particularly based on human visual property in order to perform encode control on the video signals. 
         [0004]    2. Description of the Related Art 
         [0005]    As an encode system based on human spatio-temporal visual property, there is proposed a system in Patent Literature 1 described later. In the Patent Literature 1, there is disclosed a technique in which an encode parameter is decided by a cost function minimizing rule using an encode distortion weighted based on a spatio-temporal visual property. 
         [0006]    On the other hand, in Patent Literature 2 and Non-Patent Literature 1, there is disclosed an encoded picture controlling system using an illusion principle by sharp/blurred repeated playback. The sharp/blurred repeated illusion means that when there are pictures at 60 frames per second, for example, if sharp pictures (high resolution pictures, 30 frames per second) and blurred pictures (low resolution pictures, 30 frames per second) are repeated every picture, the entire picture seems fairly sharp. Consequently, it is expected to improve a picture encode efficiency with a little deterioration of the picture quality.
   Patent Literature 1: Japanese Patent Application Laid-Open No. 2008-283599 Publication   Patent Literature 2: Japanese Patent Application Laid-Open No. 2009-100433 Publication   Non-Patent Literature 1: “Repetition of Sharp/Blurred TV Pictures and Its Application to Frame Interpolation (TFI)-Extension of Signal Processing of Visual Perception” Journal of The Institute of Image Information and Television Engineers 63(4) (727) pp. 549-552   
 
         [0010]    However, the technique described in Patent Literature 1 has a problem that the code amount cannot be drastically reduced at a high frame rate such as 60 frames per second. 
         [0011]    As described in Patent Literature 2 and Non-Patent Literature 1, since encoding low resolution pictures every picture may lead to lowering a correlation in the temporal direction, in some cases, the encode efficiency can be lowered. The system described in Patent Literature 2 and Non-Patent Literature 1 assumes that frames are uniquely decided as either sharp or blurred frames and a uniform filter processing is applied to the blurred frames in a picture. There is known that a problem occurs in which when the uniform filter processing is performed in the picture in this way, a deterioration partially occurs due to video motion property. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to provide a code amount reducing apparatus, an encoder and a decoder capable of highly reducing the code amount of a video signal for a high frame rate video without deteriorating the picture quality by processings only at the encode side. 
         [0013]    In order to achieve the object, this invention is firstly characterized in that a code amount reducing apparatus in an apparatus for performing frequency conversion such as orthogonal conversion on a predictive error signal obtained by using a correlation between video signals in the temporal or spatial direction, and then encoding said predictive error signal, comprises a target frame specifying unit for specifying a frame to be processed, a unit for acquiring a coefficient string by collectively frequency-converting, for a target frame specified in said target frame specifying unit, pixel values at predetermined area or predetermined macro block of said target frame and pixel values at the same area or macro block in the frames before and after said target frame, a unit for finding a non-perceptible coefficient based on a spatio-temporal visual property model for said coefficient string and a unit for setting said non-perceptible high frequency coefficient at 0 for a frequency conversion coefficient of orthogonal conversion of said predictive error signal. 
         [0014]    The invention is secondly characterized in that when said encode is in the intra-mode, said non-perceptible high frequency coefficient is set at 0 for said frequency conversion coefficient of orthogonal conversion of said predictive error signal, and when said encode is in the inter-mode, all said frequency conversion coefficients of orthogonal conversion of said predictive error signal are set at 0. 
         [0015]    The invention is thirdly characterized in that the apparatus further comprises an encode mode selecting unit, wherein said encode mode selecting unit selects an encode mode having a smaller code amount from among the intra-mode in which said non-perceptible high frequency coefficient is set at 0 for said frequency conversion coefficient of orthogonal conversion of said predictive error signal and the inter-mode in which all said frequency conversion coefficients of orthogonal conversion of said predictive error signal are set at 0. 
         [0016]    The invention is fourthly characterized in that an encoder for performing frequency conversion such as orthogonal conversion on a predictive error signal obtained by using a correlation between video signals in the temporal or spatial direction, and then encoding said predictive error signal, comprises a decoder for decoding an encoded video signal, a target frame specifying unit for specifying a frame to be processed, a unit for acquiring a coefficient string by collectively frequency-converting, for a target frame decoded in said decoding unit and specified in said target frame specifying unit, pixel values at predetermined area or predetermined macro block of said target frame and pixel values at the same area or macro block in the frames before and after said target frame, a unit for finding a non-perceptible coefficient based on a spatio-temporal visual property model for said coefficient string, a unit for setting said non-perceptible high frequency coefficient at 0 for a frequency conversion coefficient of orthogonal conversion of said predictive error signal, and a unit for reconstructing encoded data of said encoded video signal based on the result that said non-perceptible high frequency coefficient is set at 0. 
         [0017]    The invention is fifthly characterized in that an encoder including the code amount reducing apparatus comprises a unit for encoding encode control processing information and applied frame number information acquired from said target frame specifying unit, wherein said encode control processing information and said applied frame number information encoded by said encoding unit are inserted into a bit stream containing said frequency conversion coefficient whose code amount is reduced by said code amount reducing apparatus, and are output. 
         [0018]    The invention is sixthly characterized in that a decoder for decoding a video signal encoded by the encoder comprises a unit for separating a frequency conversion coefficient of a video signal, said encode control processing information and said applied frame number information from said bit stream, a unit for decoding said separated frequency conversion coefficient, a displaying unit for displaying a video signal acquired by said decoding, a unit for decoding said separated encode control processing information and applied frame number information, and a playback control unit for outputting a playback control signal, wherein when a control signal for slow motion playback or pause is output from said playback control unit, a processed frame specified by said target frame specifying unit from a video signal acquired by said decoding is skipped, and is not displayed on the displaying unit. 
         [0019]    According to the first to sixth features, it is possible to provide a code amount reducing apparatus or an encoder suitable to be applied to an apparatus for encoding a video signal particularly at a high frame rate (such as 60 fps, 120 fps). The code amounts of the video signals per several frames can be largely reduced without deteriorating the picture quality by the processings only at the encode side. 
         [0020]    According to the first feature, since the non-perceptible high frequency coefficient can be assumed as 0 based on the spatio-temporal visual property model for the frequency conversion coefficient of the orthogonal conversion of the predictive error signal, the code amount can be reduced with no or little deterioration of the substantial picture quality substantially. 
         [0021]    According to the second feature, since all the frequency conversion coefficients of the orthogonal conversion of the predictive error signal are assumed as 0 in the inter-mode encode, a processing load is small and the code amount can be reduced with no or little deterioration of the substantial picture quality substantially. 
         [0022]    According to the third feature, the encode mode having the smallest code amount can be selected with no or little deterioration of the substantial picture quality substantially. 
         [0023]    Further, according to the fourth feature, the encode data can be reconstructed by the processing of assuming the high frequency coefficient which cannot be perceived based on the spatia-temporal visual property mode as 0, thereby the code amount of the encoded video signal is effectively reduced. 
         [0024]    According to the fifth feature, the encode control processing information and the applied frame number information can be output to the decoder with ease and with no credibility damaged. 
         [0025]    Further, according to the sixth feature, there can be configured such that deteriorated images are not displayed during slow motion playback or pause. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a block diagram showing a schematic structure of one embodiment of the present invention; 
           [0027]      FIG. 2  is an explanatory diagram of a 3D video signal; 
           [0028]      FIG. 3  is an explanatory diagram showing a relationship between a spatio-temporal visual property model and encode control; 
           [0029]      FIG. 4  is an explanatory diagram of a spatial visual property model; 
           [0030]      FIG. 5  is an explanatory diagram of one specific example of the encode control; 
           [0031]      FIG. 6  is a block diagram showing a structure of essential parts according to a third embodiment of the present invention; 
           [0032]      FIG. 7  is a block diagram showing a structure of essential parts according to a fourth embodiment of the present invention; 
           [0033]      FIG. 8  is a conceptual diagram showing an exemplary sequence format output from an encoder according to the present invention; 
           [0034]      FIGS. 9A to 9C  are explanatory diagrams showing positions in a header where encode control processing information and applied frame number information are inserted; and 
           [0035]      FIG. 10  is a schematic block diagram of a decoder suitable for decoding a signal encoded by the encoder according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    The present invention will be described below in detail with reference to the drawings.  FIG. 1  is a block diagram for explaining one embodiment of the present invention. An explanation will be made below by way of a H.264 encoder, but the present invention is not limited thereto and is applicable to encoders using other methods. 
         [0037]    In  FIG. 1 , it is assumed that an input video signal (I) is input to be encoded in units of frames into a code amount reducing apparatus  1 . The input video signal (I) is managed in an appropriate signal form, and frame numbers and/or pixel positions can be appropriately acquired at any stage in the system. 
         [0038]    The input video signal (I) is first stored in a frame memory  10  in order of frame number such as F 1 , F 2 , . . . , F 7 . This is because information on frames before and after the frame to be encoded needs to be referred to in the later processings. Though a capacity of the frame memory  10  depends on the number of frames to be referred to in a 3D FFT (Fast Fourier Transform)  15  in the later stage, the memory  10  can store information for more than the number of frames to be referred to. 
         [0039]    A frame delaying unit  11  delays the input video signal (I) for a time for storing the information required for the processing of the 3D FFT  15  in the frame memory  10 . For example, when the frame to be encoded is F 4 , the signal (I) is delayed for the time for storing the future frames F 5  to F 7 . 
         [0040]    A sharp/blurred frame mode classifying unit  12  as target frame specifying means for specifying a frame to be processed classifies the frame F 4  to be encoded into either of sharp picture or blurred picture. It is preferable that an insertion ratio of the blurred frames into the sharp frames is such that the sharp frames and the blurred frames are repeated every frame for sharp/blurred playback, that is, at the ratio of 1:1, but the present invention is not limited thereto and may take an arbitrary ratio. The ratio of one blurred frame to two sharp frames or the ratio of one blurred frame to three sharp frames may be taken. Alternatively, the ratio may be decided according to the frame rate of the video signal. Actually, since as the frame rate is higher, the ratio of the number of blurred frames to the number of sharp frames can be increased more, there may be performed a processing of assuming 60 fps as one frame interval and, at a higher frame rate, increasing the ratio in proportion to the frame rate. The classification of sharp frame and blurred frame is made based on the frame numbers F. The sharp/blurred frame mode classifying unit  12  outputs a signal b (or binary signal 1) when the frame is classified as blurred and outputs nothing (or binary signal 0) when the frame is classified as sharp. 
         [0041]    The sharp/blurred frame mode classifying unit  12  may also decide an interval between target frames according to a frame rate of the input signal. 
         [0042]    When the frame is classified as blurred in the sharp/blurred frame mode classifying unit  12 , a switching unit  13  is powered on (closed) and the processings described later will be performed. On the other hand, when the frame is classified as sharp, the switching unit  13  remains off (opened). As a determination whether sharp/blurred playback is performed is done by an encode block, the subsequent processings will be performed in units of block. 
         [0043]    A 3D video signal extracting unit  14  extracts block 3D picture information (c), i.e. a coefficient string, as shown in  FIG. 2  from the frame memory  10 . In order to reflect the spatio-temporal property of the video, the encode blocks are extracted from the same positions of each frame of (N B +N F +1) frames made of the target frame F 4 , the past N B  frames and the future N F  frames. Assuming that the block to be processed is the block B 4  within the frame F 4  to be processed and its size is N X ×N y , the block 3D picture information (c) comprising N X ×N y ×(N B +N F +1) pixels is extracted. In the following, the block B 4  of N x ×N y  pixels is called macro block. 
         [0044]    Then, the 3D FFT  15  is applied to the block 3D picture information (c) to obtain a spatio-temporal frequency property (g). Typically, the result of the 3D FFT  15  shows the property (g) of  FIGS. 3A and 3B  without considering the folded part, and it can be shown as one straight line through the origin. The folded part surely occurs when the 3D FFT is performed, but its illustration is omitted from  FIGS. 3A and 3B . A sign (h) in  FIGS. 3A and 3B  indicates a visual passband. A spatial frequency component outside the visual passband (h) of the spatia-temporal frequency property (g) is not perceptible by human eyes. The horizontal axis of  FIG. 3A  indicates the spatial frequency ω x  and the longitudinal axis indicates the temporal frequency ω T .  FIG. 3B  three-dimensionally shows the relationship between ω x  and ω T , where ω 0  indicates the spatial frequency in the vertical direction and ω 1  indicates the spatial frequency in the horizontal direction. 
         [0045]      FIG. 4  shows a spatial visual property model  16  (see  FIG. 1 ). Since the visual passband (h) has a human visual pass property that the passband in the spatial frequency direction is wider in a lower temporal frequency f (f 0  in  FIG. 4 ) and is narrower as the temporal frequency is higher (f 0 →f 1 →f 2  in  FIG. 4 ), the spatial visual property model is designed assuming that the model has a cone-like shape as shown in  FIG. 4 . Since the specific frequency property depends on the resolution of a motion picture to be encoded and the sizes of display systems (monitor, projector), it is suitable that the model is separately designed. The cone of  FIG. 4  indicates the visual passband (h) of  FIG. 3  and means that the inside of the cone is the passband. 
         [0046]    Turning to  FIG. 1 , an intersection coordinate calculating unit  17  obtains the spatial frequency coordinate (ω 0 ′, ω 1 ′) at the intersection between the spatia-temporal frequency property (g) and the visual passband (h). In other words, as shown in  FIG. 3B , the spatial frequency coordinate (ω 0 ′, ω 1 ′) at the intersection (g′) is obtained. The spatial frequency coordinate (ω 0 ′, ω 1 ′) indicates the spatial frequency at the boundary where human eyes cannot perceive. 
         [0047]    The input video signal is input into an encoder  21 , (for example, a H.264 encoder) via the frame delaying unit  11  to be subjected to intra-encode (intra-prediction) or inter-encode (motion compensation). An encode coefficient (d) obtained by the intra-encode or inter-encode is divided into the sharp and blurred frames in a switching unit  22  which is switched by the sharp/blurred frame mode signal (b). As well known, the intra-encode and the inter-encode comprise a plurality of encode modes, respectively. 
         [0048]    When the blurred frame mode, the encode coefficient (d) in each encode mode is transmitted to a coefficient cut processing unit  23 , while, when the sharp frame mode, the encode coefficient (d) is transmitted to a next processing unit as usual without any processing by the present invention. The coefficient cut processing unit  23  performs the processing in which the high frequency component of the encode coefficient (or conversion coefficient) of the macro block predictive error signal (called residue signal below) is cut according to the spatial frequency coordinate (ω 0 ′, ω 1 ′) found in the intersection coordinate calculating unit  17 . 
         [0049]    In other words, in the coefficient cut processing unit  23 , the high frequency component not perceptible by human eyes is assumed as 0 according to the spatial frequency coordinate (ω 0 ′, ω 1 ′), and is removed from the components to be encoded. Consequently, the conversion coefficient having a higher frequency than the spatial frequency coordinate (ω 0 ′, ω 1 ′) does not need to be transmitted, thereby reducing the code amount. 
         [0050]    There will be described below with reference to  FIG. 5  one specific example of the processing of assuming the conversion coefficient of the macro block residue signal obtained by the intra-encode or inter-encode as 0 according to the spatial frequency coordinate (ω 0 ′, ω 1 ′). Assuming that the matrix of the orthogonal conversion coefficient of the residue signal is made in 4×4 size, M and N meeting the following equation (1) are found and the coefficients meeting m≧M and n≧N are assumed as zero for the index (m, n) of the orthogonal conversion coefficient. 
         [0000]      ( M/ 4)π≦|ω 0 ′|&lt;(( M+ 1)/π), ( N/ 4)π≦|ω 1 ′|&lt;(( N+ 1)/π) (where, M, N=0, 1, 2, 3)  (1)
 
         [0051]    For example, when the matrix in 4×4 size of the residue signal  30  is as shown in  FIG. 5  and in the case of M=1 and N=2, a frequency component outside the frequency component at the position (1, 2) may be assumed as 0 as illustrated. 
         [0052]    Reference numeral  51  in  FIG. 1  indicates an encoder for an applied information of encode control and Reference numeral  52  indicates a muxer, and their functions will be described later. 
         [0053]    A second embodiment of the present invention will be described below. As a result of the experiment of the present invention by the present inventors, it is found that even when the encode coefficient (d) or the residue signal is neglected (that is, not coded) for the macro block of the blurred frame subjected to the inter-encode in the encoder  21  of  FIG. 1 , the picture quality is not largely influenced. Thus, it is found that it is suitable that the coefficient cut by the spatio-temporal frequency property (g) is applied only to the residue signal of the macro block subjected to the intra-encode of the blurred frame. 
         [0054]    A third embodiment of the present invention will be described below with reference to  FIG. 6 . The embodiment is such that a mode selecting unit  25  is added to the second embodiment thereby to select an encode mode having a small code amount. The same reference numerals are denoted to the blocks having the same or similar functions as those of  FIG. 1 . 
         [0055]    The input video signal (I) delayed in the frame delaying unit  11  of  FIG. 1 , for example, is input into the encoder  21  of  FIG. 6 . The switching unit  22  is controlled by the sharp/blurred frame mode classifying signal (b), is connected to one illustrated position for the blurred frame, and is connected to the other position for the sharp frame. The mode selecting unit  25  is input an intra-mode encode coefficient having the residue signal subjected to the code amount reduction processing in the coefficient cut processing unit  23  and an inter-mode encode coefficient for which a conversion coefficient value of the residue signal is assumed as 0 in a Not Coded unit  24 . The mode selecting unit  25  obtains the code amount of each encode coefficient in the intra-mode and the inter-mode, and selects the encode mode having the smallest code amount. On the other hand, the sharp frame encode coefficient is directly transmitted to the mode selecting unit  25  not via the coefficient cut processing unit  23  and the Not Coded unit  24 , and is subjected to the conventional mode selection processing. The mode selecting unit  25  can select the encode mode by a well-known rate distortion optimization processing, for example. 
         [0056]    A fourth embodiment when an encoded video signal (I′) is input as the input video signal (I) will be described below with reference to  FIG. 7 . The same reference numerals are denoted to the blocks having the same or similar functions as those of  FIGS. 1 and 6 . The processings with numerals  15  to  17  of  FIG. 1  are inserted at the dotted line between the 3D video signal extracting unit  14  and the coefficient cut processing unit  23  based on the visual property model in  FIG. 7 , but an illustration thereof will be omitted for a simplified explanation. 
         [0057]    When the encoded video signal (I′) is input, the encoded video signal (I′) is input into a decoder  31 , a MB (macro block) classifying unit  32  for odd-numbered frames and B pictures and an intra-/inter-deciding unit  33 . The decoder  31  decodes the encoded video signal (I′). The MB classifying unit  32  for odd-numbered frames and B pictures is means for specifying a frame and MB to be processed, i.e. a target frame and MB, and performs the similar processings to the sharp/blurred frame classifying unit  12 . Specifically, the MB classifying unit  32  detects the MB which is an odd-numbered frame and a B picture not referred to by other picture from the encoded video signal (I′), and powers on or closes the switching unit  13  on the detection. Thus, the 3D video signal extracting unit  14  extracts a 3D video signal made of the MB which is an odd-numbered frame and a B picture from the video signal decoded in the decoding unit  31 . The MB classifying unit  32  may also decide an interval between target frames according to a frame rate of the input signal. Thereafter, the 3D video signal passes the processings with numerals  15  to  17  of  FIG. 1 , but the processings are the same as those of  FIG. 1  and thus an explanation thereof will be omitted. 
         [0058]    In the intra-/inter-deciding unit  33 , the encoded video signal (I′) is decided which of the intra-mode or the inter-mode is used for the encoding. In the case of the intra-mode, the MB which is an odd-numbered frame and a B picture is transmitted to the coefficient cut processing unit  23  which processes based on the visual property model, and the high frequency component of the residue signal is subjected to the cut processing. In the case of the inter-mode, the MB which is an odd-numbered frame and a B picture is transmitted to the Not Coded unit  24  and the conversion coefficient of the residue signal is set at 0. An encoded data reconstructing unit  34  reconstructs and outputs the encoded data of the encoded video signal (I′) based on the input result. 
         [0059]    On the other hand, the intra- or inter-encoded video signal not corresponding to the MB which is an odd-numbered frame and a B picture is output as it is without being subjected to the coefficient cut processing or the processing by the Not Coded unit and without the reconstruction of the encoded data. 
         [0060]    The functions of the encoder for the applied information of encode control  51  and the muxer  52  (see  FIG. 1 ) will be described below in detail. The functions also are applicable to the embodiments in  FIGS. 6 and 7 . 
         [0061]    The encoder for the applied information of encode control  51  encodes (1) information on whether the sharp/blurred encode control processing is applied (which will be referred to as encode control processing information below) and (2) information on an applied frame number when the sharp/blurred encode control processing is applied. The encode control processing information and the applied frame number information can be acquired from the sharp/blurred frame mode classifying unit  12 . The encode control processing information and the applied frame number information, which are encoded in the encoder for the applied information of encode control  51 , are sent to the muxer  52 . 
         [0062]    The muxer  52  contains the encoded encode control processing information and applied frame number information within a sequence in which image information to which the sharp/blurred encode control processing is applied is sent as a bit stream, and outputs the same. The encoded encode control processing information and applied frame number information also may be separately sent without being contained in the sequence. 
         [0063]    Reference numeral  53  indicates an output signal of the muxer  52 . A specific example in which the encoded encode control processing information and applied frame number information are inserted into the sequence will be described with reference to  FIG. 8 .  FIG. 8  is a conceptual diagram of the sequence format, where the sequence is configured of a sequence header  53   a , a frame header  53   bn , and image data made of image data  53  cn (n=0, 1, 2, 3, . . . ). Herein, n indicates a frame number of an image signal. The encoded encode control processing information and applied frame number information can be inserted at position (p) of the sequence header  53   a  or in the frame header  53   bn . The exemplary insertion will be described with reference to  FIGS. 9A to 9C . 
         [0064]    In  FIG. 9A , the flag (f) of the encode control processing information, that is, the flag (f) indicating whether the sharp/blurred processing is applied, and a number string (r) (made of 0 or 1) indicating a sharp/blurred processed frame are contained at position (p) of the sequence header  53   a . In the number string (r), “1” indicates a sharp frame and “0” indicates a blurred frame. Reversely, “0” may indicate the sharp frame and “1” may indicate the blurred frame. 
         [0065]    In  FIG. 9B , the flag (f) of the encode control processing information, that is, the flag (f) indicating whether the sharp/blurred processing is applied, the first blurred applied frame number (s), and applied frame interval information (t) are contained at position (p) of the sequence header  53   a . In the illustrated example, since s=1 and t=2 are assumed, the first blurred applied frame is the first frame, and the blurred frame is subsequently applied per frame. 
         [0066]    In  FIG. 9C , the flag (f) indicating whether the corresponding frame is a blurred frame or a sharp frame is inserted in the frame header  53   bn . In the illustrated example, there is shown that the 0-th frame is a sharp frame (1), the first frame is a blurred frame (O), the second frame is a sharp frame (1), . . . . 
         [0067]    One embodiment of a reproducing apparatus will be described below with reference to  FIG. 10 .  FIG. 10  is a schematic block diagram of the reproducing apparatus, where the reproducing apparatus has a playback control unit  61 , a displaying unit  62  and a demuxer  63  for separating multiplexed information. 
         [0068]    The demuxer  63  is input multiplexed image information such as the output signal  53 . The demuxer  63  separates header information  64  and image data  65  from the multiplexed image information. A header data extracting unit  66  extracts the flag (f) of the encode control processing information and the applied frame number information at position (p) from the sequence header  53   a , and sends them to a decoder  67 . The decoder  67  decodes the flag (f) and the applied frame number information. An applied frame number signal (q 1 ) acquired by the decoding is sent to a first switching unit (SW 1 ). On the other hand, a frequency conversion coefficient of the image data  65  is extracted by a frequency conversion coefficient extracting unit  68  and is decoded by a decoder  69 . 
         [0069]    Instruction signals (q 2 ) such as normal playback, slow motion playback and pause are output from a playback control unit  61  and sent to a second switching unit SW 2 . The second switching unit SW 2  selects contact (a) when the instruction signal (q 2 ) is for slow motion playback and pause, and selects contact (b) in other cases. The first switching unit SW 1  is turned off (open) when the applied frame number signal (q 1 ) is for a blurred frame, and turned on (close) when the applied frame number signal q 1  is for a sharp frame. 
         [0070]    Thereby, when the second switching unit SW 2  is connected to contact (b) during normal playback, the decoded sharp and blurred frames are displayed on the displaying unit  62 . However, during slow motion playback or pause, since the second switching unit SW 2  is connected to contact (a) and the first switching unit SW 1  is turned off (open) or on (close) by the applied frame number signal (q 1 ) as described above, the blurred frame is skipped and is not displayed on the displaying unit  62 . 
         [0071]    The first and second switching units SW 1  and SW 2  are merely exemplary for simplified explanation, and can be realized by a circuit, such as a logic circuit having a similar function to the switching units. 
         [0072]    According to the embodiments, the blurred frames are not displayed on the displaying unit  62  during slow motion playback or pause, thereby preventing deteriorated images from being displayed. 
         [0073]    The present invention has been described above using the preferred embodiments, but the present invention is not limited to the embodiments, and it is clear that various modifications may be made within the scope of the present invention.