Patent Publication Number: US-2011058611-A1

Title: Video encoding apparatus, video encoding method, video encoding program, video decoding apparatus, video decoding method and video decoding program

Description:
RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 10/810,792 filed on Mar. 26, 2004, which claims priority to JP 2003-088618 filed on Mar. 27, 2003, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a video encoding apparatus, a video encoding method, a video encoding program, a video decoding apparatus, a video decoding method, and a video decoding program. 
     2. Description of the Related Art 
     Generally, in a video encoding apparatus, a coding target frame is divided into a plurality of blocks of predetermined size, and motion compensation prediction between each of the blocks and a prediction reference image of a predetermined region in a reference frame is performed so that motion vectors are detected, thus producing a predicted image of the coding target frame. In the video encoding apparatus, the coding target frame is expressed by motion vectors from the reference frame, so that the redundancy existing in the time direction is reduced. Furthermore, a prediction residual image based on a difference between the coding target frame and the predicted image is converted by DCT (Discrete Cosine Transform), and is expressed as a set of DCT coefficients, so that the redundancy existing in the spatial direction is reduced. 
     In the abovementioned video encoding apparatus, in order to achieve a further reduction of the redundancy existing in the time direction, the motion compensation prediction is performed with a high resolution by disposing interpolated pixels at the ½ pixel positions or ¼ pixel positions between the integer pixels of the reference frame, so that the encoding efficiency is improved. A pixel value obtained by applying linear filter of (1, −5, 20, 20, −5, 1)/16 to 6 integer pixels that include 3 neighborhood integer pixels each on the left and right is given to the interpolated pixel that is located in the ½ pixel position between the integer pixels that are lined up in the horizontal direction. A pixel value obtained by applying a linear filter of (1, −5, 20, 20, −5, 1)/16 to 6 integer pixels that include 3 neighborhood integer pixels each above and below is given to the interpolated pixel that is located in the ½ pixel positions between the integer pixels that are lined up in the vertical direction. A mean value of the pixel values of interpolated pixels in the ½ pixel positions which are adjacent in the horizontal direction is given to the interpolated pixel that is located at equal distances from four neighborhood integer pixels. Furthermore, a linearly interpolated value from two pixels among the neighborhood integer pixels or interpolated neighborhood pixels in the ½ pixel positions is given to the interpolated pixel that is in the ¼ pixel position. Namely, pixel values obtained by applying filtering to neighborhood integer pixels are given to the interpolated pixels, so that even in cases where the difference between the reference frame and the coding target frame is large. Thus the redundancy is effectively reduced. 
     Here, a video encoding apparatus is known in which motion compensation prediction is performed by giving the means values of four neighborhood integer pixels to the pixels at the (¾, ¾) pixel positions in order to improve the filtering effect further (for example, see G. Bjontegaard, “Clarification of “Funny Position””, ITU-T SG 16/Q15, doc. Q15-K-27, Portland, 2000.). In such a video encoding apparatus, the interpolated pixels are provided by using low-pass filters of which spectral band-pass in low frequency band is narrower than filter corresponding to linear interpolation, thereby improving the effect of filtering further. As a result, the redundancy is reduced. The interpolated pixels to which low-pass filters of which spectral band-pass in low frequency band is narrow are applied are called “Funny Positions”. 
     SUMMARY OF THE INVENTION 
     In the abovementioned video encoding apparatus, the following problem is encountered: namely, although the redundancy is reduced by providing the funny positions in the case of blocks of the coding target frame in which the variation from the reference frame is large, the provision of the funny positions increase the difference from the reference frames in the case of blocks of the coding target frame in which the variation from the reference frame is small, so that the effect of achieving high resolution of motion compensation prediction is lost. 
     The present invention was devised in order to solve the abovementioned problem; it is an object of the present invention to provide a video encoding apparatus, video encoding method, and video encoding program which allow the realization of an improvement in the encoding efficiency due to an increase in the resolution of motion compensation prediction and an improvement in the encoding efficiency due to filtering, and a video decoding apparatus, video decoding method, and video decoding program which restore a video from compressed data generated by the video encoding apparatus of the present invention. 
     In order to solve the abovementioned problem, a video encoding invention comprises motion compensation prediction means for generating a predicted image of a coding target frame by dividing the coding target frame into a plurality of blocks, generating a prediction reference image that are formed by providing interpolated pixels which are produced by interpolation between integer pixels from integer neighborhood pixels in a predetermined region of a reference frame, and determining a motion vector for the prediction reference image for each of the plurality of blocks. The motion compensation prediction means has complexity extraction means for extracting complexity information which indicates a degree of complexity of movement from the reference frame for each of the plurality of blocks; and predicted image generating means for generating the predicted image by using the prediction reference image to which filtering pixels are provided in accordance with the complexity information on the basis of a predetermined rule which increases the number of the filtering pixels which have pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics to neighborhood integer pixels. 
     A video encoding apparatus of another aspect of the present invention includes a motion compensation prediction step in which motion compensation prediction means generates a predicted image of a coding target frame by dividing the coding target frame into a plurality of blocks, generating a prediction reference image that is formed by providing interpolated pixels which are produced by interpolation between integer pixels from integer neighborhood pixels in a predetermined region of a reference frame, and determining a motion vector for the prediction reference image for each of the plurality of blocks. In the motion compensation prediction step, complexity extraction means extracts complexity information which indicates a degree of complexity of movement from the reference frame for each of the plurality of blocks, and predicted image generating means generates the predicted image by using the prediction reference image to which filtering pixels are provided in accordance with the complexity information on the basis of a predetermined rule which increases the number of the filtering pixels which have pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics to neighborhood integer pixels. 
     A video encoding of still another aspect of the present invention causes a computer to function as motion compensation prediction means for generating a predicted image of a coding target frame by dividing the coding target frame into a plurality of blocks, generating a prediction reference image that is formed by providing interpolated pixels which are produced by interpolation between integer pixels from integer neighborhood pixels in a predetermined region of a reference frame, and determining a motion vector for the prediction reference image for each of the plurality of blocks. The motion compensation prediction means has: complexity extraction means for extracting complexity information which indicates a degree of complexity of movement from the reference frame for each of the plurality of blocks; and predicted image generating means for generating the predicted image by using the prediction reference image to which filtering pixels are provided in accordance with the complexity information on the basis of a predetermined rule which increases the number of the filtering pixels which have pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics to neighborhood integer pixels. 
     According to the abovementioned present invention, the complexity information indicating the degree of complexity of movement with respect to the reference frame is extracted for each of a plurality of blocks into which the coding target frame is divided. The number of filtering pixels which are given pixel values obtained by applying low-pass filters each of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics in the prediction reference image is increased in accordance with the degree of complexity specified by such complexity information. Namely, in the case of blocks in which the variation from the reference frame is small, the predicted image is generated by using the prediction reference image with high resolution in which the number of filtering pixels is reduced, so that the precision of the motion compensation prediction is improved; accordingly, the redundancy is reduced. On the other hand, in the case of blocks in which the variation from the reference frame is large, the predicted image are generated by using the prediction reference image in which the number of filter pixels is increased. Accordingly, the difference between the predicted image and the processing target block is reduced. As a result, the redundancy is reduced. As described above, since the number of filtering pixels is flexibly altered in accordance with the variation from the reference frame for each block of the coding target frame, the encoding efficiency is improved. 
     In the present invention, the complexity extraction means can use an absolute value of a differential motion vector of a block surrounding the block for which the complexity information is to be extracted as the complexity information. 
     Furthermore, in the present invention, conversion means converts predicted residual difference image produced by calculating a difference between the coding target frame and the predicted image into a set of coefficients on the basis of a predetermined conversion rule. In this case, the complexity extraction means can use the numbers of non-zero coefficients among the coefficients in a block surrounding the blocks for which the complexity information is to be extracted as the complexity information. 
     Furthermore, in the present invention, the complexity extraction means can use an absolute value of a differential motion vector of the blocks for which complexity information is to be extracted as the complexity information. 
     In addition, a video decoding apparatus of the present invention comprises motion compensation prediction means for generating a prediction reference image that is formed by providing interpolated pixels which are produced by interpolation between integer pixels from integer neighborhood pixels in a predetermined region of a reference frame, and generating a predicted image by dividing the decoding target frame into a plurality of blocks, and performing motion compensation based on a motion vector included in compression data by using the prediction reference image. The motion compensation prediction means has: complexity extraction means for extracting complexity information which indicates a degree of complexity of movement from the reference frame for each of the plurality of blocks; and predicted image generating means for generating the predicted image by using the prediction reference image to which filtering pixels are provided in accordance with the complexity information on the basis of a predetermined rule which increases the number of the filtering pixels which have pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics to neighborhood integer pixels. 
     A video decoding method of another aspect of the present invention includes motion compensation prediction step in which motion compensation prediction means generates a prediction reference image that is formed by providing interpolated pixels which are produced by interpolation between integer pixels from integer neighborhood pixels in a predetermined region of a reference frame, and generates a predicted image by dividing the decoding target frame into a plurality of blocks and performing motion compensation based on a motion vector included in compression data by using the prediction reference image. In the motion compensation prediction step, complexity extraction means extracts complexity information which indicates a degree of complexity of movement from the reference frame for each of the plurality of blocks, and predicted image generating means generates the predicted image by using the prediction reference image to which filtering pixels are provided in accordance with the complexity information extracted by the complexity extraction means on the basis of a predetermined rule which increases the number of the filtering pixels which have pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics to neighborhood integer pixels. 
     A video decoding program of still another aspect of the present invention causes a computer to function as motion compensation prediction means for generating a prediction reference image that are formed by providing interpolated pixels which are produced by interpolation between integer pixels from integer neighborhood pixels in a predetermined region of a reference frame, and generating a predicted image by dividing the decoding target frame into a plurality of blocks, and performing motion compensation based on a motion vector included in compression data by using the prediction reference image. The motion compensation prediction means has: complexity extraction means for extracting complexity information which indicates a degree of complexity of movement from the reference frame for each of the plurality of blocks; and predicted image generating means for generating the predicted image by using the prediction reference image to which filtering pixels are provided in accordance with the complexity information extracted by the complexity extraction means on the basis of a predetermined rule which increases the number of the filtering pixels which have pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics to neighborhood integer pixels. 
     According to the present invention, motion vectors are decoded from compressed data produced by the abovementioned video encoding apparatus or by a computer operated by the abovementioned video encoding program. Furthermore, for each of the plurality of blocks of the decoding target frame, the complexity information indicating the degree of complexity of the movement from the reference frame is extracted. The prediction reference image in which the number of filtering pixels which have pixel values produced by applying low-pass filters each of which spectral band-pass in low frequency band is narrow among a plurality of low-pass filters with different high-frequency cutoff characteristics are increased in accordance with the degree of complexity of the movement specified by such complexity information are produced. The predicted image is produced from the prediction reference image using the abovementioned motion vectors. Accordingly, a video can be restored from the compressed data produced by the abovementioned video encoding apparatus or by a computer operated by the abovementioned video encoding program. 
     In the abovementioned present invention, the complexity extraction means can use an absolute value of a differential motion vector of a block surrounding the block for which the complexity information is to be extracted as the complexity information. 
     Furthermore, in the abovementioned present invention, decoding means decodes compression data including compression codes. The compression code is generated by converting predicted residual difference image produced by calculating a difference between the decoding target frame and the predicted image into a set of coefficients on the basis of a predetermined conversion rule and encoding the set of coefficients. In this case, the complexity extraction means can use the numbers of non-zero coefficients among the coefficients in a block surrounding the blocks for which the complexity information is to be extracted as the complexity information. 
     Furthermore, in the abovementioned present invention, the complexity extraction means can use an absolute value of a differential motion vector of the blocks for which complexity information is to be extracted as the complexity information. 
     The present invention will be more fully understood from the detailed description given hereinbelow and the attached drawings, which are given by way of illustration only and are not to be considered as limiting the present invention. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the course of the following detailed description, reference will be made to the attached drawings in which: 
         FIG. 1  is a block diagram which shows the functional configuration of a video encoding apparatus of a first embodiment; 
         FIG. 2  is a block diagram which shows the configuration of the motion compensation prediction unit provided in the video encoding apparatus of the first embodiment; 
         FIG. 3  is a schematic view of an example of a first prediction reference image generated by a first FP production unit provided in the video encoding apparatus of the first embodiment; 
         FIG. 4  is a schematic view of an example of a second prediction reference image produced by a second FP production unit provided in the video encoding apparatus of the first embodiment; 
         FIG. 5  is a flow chart which shows a video encoding method of a first embodiment; 
         FIG. 6  is a flow chart relating to motion compensation prediction in the video encoding method of the first embodiment; 
         FIG. 7  is a block diagram which shows the configuration of a video encoding program relating to a first embodiment; 
         FIG. 8  is a block diagram which shows the configuration of the motion compensation prediction module in the video encoding program of the first embodiment; 
         FIG. 9  is a block diagram which shows the configuration of an alternative motion compensation prediction unit in the video encoding apparatus of the first embodiment; 
         FIG. 10  is a flow chart relating to alternative motion compensation prediction in the video encoding method of the first embodiment; 
         FIG. 11  is a diagram which shows the configuration of an alternative motion compensation prediction module in the video encoding program of the first embodiment; 
         FIG. 12  is a block diagram which shows the functional configuration of a video encoding apparatus of a second embodiment; 
         FIG. 13  is a block diagram which shows the functional configuration of a video encoding apparatus constituting a third embodiment; 
         FIG. 14  is a block diagram which shows the configuration of the motion compensation prediction unit of the video encoding apparatus of the third embodiment; 
         FIG. 15  is a flow chart which shows the processing of the motion compensation prediction in the third embodiment; 
         FIG. 16  is a diagram which shows the configuration of the motion compensation prediction module of a video encoding program relating to a third embodiment; 
         FIG. 17  is a block diagram which shows the functional configuration of a video decoding apparatus relating to a fourth embodiment; 
         FIG. 18  is a block diagram which shows the configuration of the motion compensation prediction unit of the video decoding apparatus of the fourth embodiment; 
         FIG. 19  is a flow chart of a video decoding method relating to a fourth embodiment; 
         FIG. 20  is a flow chart showing processing relating to the motion compensation prediction of the video decoding method of the fourth embodiment; 
         FIG. 21  is a diagram which shows the configuration of a video decoding program relating to a fourth embodiment; 
         FIG. 22  is a block diagram which shows the configuration of an alternative motion compensation prediction unit in the video decoding apparatus of the fourth embodiment; 
         FIG. 23  is a diagram which shows the configuration of an alternative motion compensation prediction module in the video decoding program of the fourth embodiment; 
         FIG. 24  is a block diagram which shows the functional configuration of a video decoding apparatus relating to a fifth embodiment; 
         FIG. 25  is a block diagram which shows the functional configuration of a video decoding apparatus constituting a sixth embodiment; 
         FIG. 26  is a block diagram which shows the configuration of the motion compensation prediction unit of the video decoding apparatus of the sixth embodiment; 
         FIG. 27  is a flow chart which shows the processing of motion compensation prediction in a video decoding method relating to a sixth embodiment; 
         FIG. 28  is a diagram which shows the configuration of a video decoding program relating to a sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below. Furthermore, in the description relating to the following embodiments, the same symbols are applied to the same or corresponding units in the respective figures in order to facilitate understanding of the description. 
     First Embodiment 
     A video encoding apparatus  1  of a first embodiment of the present invention will be described. In physical terms, the video encoding apparatus  1  is a computer comprising a CPU (central processing unit), a memory apparatus called a memory, a storage apparatus called a hard disk, and the like. Here, in addition to ordinary computers, such as personal computers or the like, the term “computer” also includes portable information terminals such as mobile communications terminals, so that the concept of the present invention can be widely applied to apparatus that are capable of information processing. 
     Next, the functional configuration of the video encoding apparatus  1  will be described.  FIG. 1  is a block diagram which shows the functional configuration of the video encoding apparatus  1 . The video encoding apparatus  1  functionally comprises a motion compensation prediction unit  2 , a frame memory  4 , a subtraction unit  6 , a conversion unit  8 , a quantizing unit  10 , an encoding unit  12 , an inverse quantizing unit  14 , an inverse conversion unit  16 , an addition unit  18 , and an MVD storage unit  20 . 
     The motion compensation prediction unit  2  performs motion compensation prediction using a reference frame that is stored in the frame memory  4 , thereby determining differential motion vectors (hereafter, a differential motion vector is referred to as “MVD”) and producing a predicted image of a coding target frame. The MVD is differential vector formed by a motion vector of a processing target block and intermediate value of motion vectors in blocks surrounding the processing target block. Details of the motion compensation prediction unit  2  will be described later. 
     The subtraction unit  6  calculates a difference between the predicted image produced by the motion compensation prediction unit  2  and the coding target frame so that the subtraction unit  6  generates a predicted residual difference image. 
     The conversion unit  8  decomposes the predicted residual difference image into a set of coefficients on the basis of a predetermined conversion rule. For example, DCT (Discrete Cosine Transform) can be used as the predetermined conversion rule. In the case where DCT is used, the predicted residual difference image is converted into a set of DCT coefficients. Furthermore, besides DCT, the matching pursuits method (hereafter referred to as the “MP method”) can be used as the predetermined conversion rule. The MP method is a method in which the predicted residual difference image is used as the initial residual component, and processing in which the residual component is decomposed using a basis set on the basis of Equation (1) shown below is repeated. Here, in Equation (1), f indicates the predicted residual image, R n f indicates the residual component after the n-th repetitive operation, g kn  indicates the basis that maximizes the inner product with R n f, and R m f indicates the residual component after the m-th repetitive operation. That is, according to the MP method, the basis which maximizes an inner product value with a residual component is selected from the basis set, and the residual component is decomposed into the selected basis and a largest inner product value which is a coefficient for multiplication with this basis. 
     
       
         
           
             
               
                 
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     The quantizing unit  10  generates quantized coefficients by applying a quantizing operation to the coefficients generated by decomposing the predicted residual image by the conversion unit  8 . 
     The encoding unit  12  generates a compression code that is obtained by encoding the MVD produced by the motion compensation prediction unit  2 . Furthermore, the encoding unit  12  generates a compression code that is obtained by encoding the quantized coefficients produced by the quantizing unit  10 . The encoding unit  12  produces compressed data that contains these compression codes. For example, entropy coding such as arithmetic coding can be used for this encoding processing. 
     The inverse quantizing unit  14 , inverse conversion unit  16 , and addition unit  18  are units that perform processing that is used to store the reference frame in the frame memory  4 . The inverse quantizing unit  14  inversely quantizes the quantized coefficients that have been obtained by the quantizing unit  10 . Using the coefficients generated by the inverse quantizing unit  14 , the inverse conversion unit  16  performs conversion processing that is the inverse of the conversion processing performed by the conversion unit  8 , thereby restoring the predicted residual image. The addition unit  18  produces a reference frame by adding the predicted image of the reference frame and the predicted residual image restored by the inverse conversion unit  16 . The reference frame is stored in the frame memory  4 , as described above, and is used in the processing performed by the motion compensation prediction unit  2  that generates a predicted image of a next coding target frame. 
     The MVD storage unit  20  stores the MVDs that are generated by the motion compensation prediction unit  2 . The MVDs stored in the MVD storage unit  20  are used in the processing performed by the motion compensation prediction unit  2  (described later). 
     The motion compensation prediction unit  2  will be described in detail below. The motion compensation prediction unit  2  divides the coding target frame into a plurality of blocks of a predetermined size. For each of the plurality of blocks, the motion compensation prediction unit  2  detects a motion vector to the reference frame, and uses the reference frame to generate the predicted image of the coding target frame.  FIG. 2  is a block diagram which shows the configuration of the motion compensation prediction unit  2 . The motion  23  compensation prediction unit  2  comprises a prediction reference region production unit  24 , a first FP production unit  26 , a second FP production unit  28 , a first prediction reference region storage unit  30 , a second prediction reference region storage unit  32 , a motion vector generation unit  34 , a reference region selector  36 , a predicted image production unit  38 , and a prediction error decision unit  40 . 
     The prediction reference region production unit  24  generates the prediction reference image on the basis of the. reference frame RI stored in the frame memory  4 . The prediction reference region production unit  24  comprises a ½ pixel interpolation region production unit  42  and a ¼ pixel interpolation region production unit  44 . 
     The ½ pixel interpolation region production unit  42  provides interpolated pixels in the ½ pixel positions between the integer pixels of the reference frame, and thus converts the reference frame into image with a doubled resolution. Pixel values that are produced by applying a linear filter of (1, −5, 20, 20, −5, 1)/16 to a total of 6 integer pixels (3 neighborhood integer pixels each on the left and right) are given to the interpolated pixels that are located in the ½ pixel positions sandwiched between integer pixels that are lined up in the horizontal direction. Pixel values that are produced by applying a linear filter of (1, −5, 20, 20, −5, 1)/16 to a total of 6 integer pixels (3 nearby integer pixels each above and below) are given to the interpolated pixels that are located in the ½ pixel positions sandwiched between integer pixels that are lined up in the vertical direction. The mean values of the pixel values of interpolated pixels in the ½ pixel positions that are adjacent in the horizontal direction are given as pixel values to the interpolated pixels that are located at equal distances from four neighborhood integer pixels. 
     The ¼ pixel interpolation region production unit  44  further provides interpolated pixels to the image with a doubled resolution produced by the ½ pixel interpolation region production unit  42 , thus producing an image in which the resolution of the reference frame is quadrupled. Values that are linearly interpolated from 2 pixels among the neighborhood integer pixels and interpolated pixels in the ½ pixel positions are given to these interpolated pixels as pixel values. The reference frame is converted into the image with a quadrupled resolution by the ½ pixel interpolation region production unit  42  and ¼ pixel interpolation region production unit  44 , and the image is output to the first FP production unit  26  and second FP production unit  28  as the prediction reference image. 
     The first FP production unit  26  produces a first prediction reference image in which pixel values produced by applying a low-pass filter of which spectral band-pass in low frequency band is narrow to the prediction reference image are given to the (¾, ¾) pixel positions. The first FP production unit  26  stores the first prediction reference image in the first prediction reference region storage unit  30 . Hereafter, in the present specification, each of the interpolated pixels provided with pixel values obtained by applying low-pass filters each of which spectral band-pass in low frequency band is narrow to integer pixels will be referred to as “FP (funny position)”. Furthermore, low-pass filters each of which spectral band-pass in low frequency band is narrow will be referred to as “low-pass filters”. 
       FIG. 3  is a schematic view of an example of a first prediction reference image generated by a first FP production unit provided in the video encoding apparatus of the first embodiment. The circles in  FIG. 3  indicate pixels. In  FIG. 3 , the solid black circles indicate integer pixels, and the empty circles indicate interpolated pixels. Furthermore, the circles with lattice-form hatching indicate the FPs. The first FP production unit  26  provides a pixel value determined by adding values which are calculated by multiplying each of the pixel values of four neighborhood integer pixels which are located directly under the FP and lined up in the horizontal direction by a coefficient of ½ to each of the FPs. 
     The second FP production unit  28  produces a second prediction reference image which is provided with a greater number of FPs than in the case of the first FP production unit  26 . The second FP production unit  28  stores the second prediction reference image in the second prediction reference region storage unit  32 .  FIG. 4  is a schematic view of an example of a second prediction reference image produced by a second FP production unit provided in the video encoding apparatus of the first embodiment. In  FIG. 4  as in  FIG. 3 , circles indicate pixels. In  FIG. 4 , the solid black circles indicate integer pixels, the empty circles indicate interpolated pixels, and the circles shown with hatching indicate FPs. 
     The second FP production unit  28  gives pixel values produced as described below to the FPs. A pixel value obtained by applying a one-dimensional low-pass filter with coefficients of ( 4/32, 24/32, 4/32) to three neighborhood integer pixels, which are lined up in the horizontal and located in direction immediately above the FP, is given to each of the FP at the (¼, ¼) pixel positions shown with diagonal hatching in  FIG. 4 . A pixel value obtained by applying a one-dimensional low-pass filter with coefficients of (− 2/32, 1/32, 17/32, 17/32, 1/32, − 2/32) to six neighborhood integer pixels, which are lined up in the horizontal direction and located immediately above the FP, is given to each of the FPs at the (¾, ¼) pixel positions shown with vertical hatching. A pixel values obtained by applying a one-dimensional low-pass filter with coefficients of ( 2/32, 6/32, 8/32, 8/32, 2/32) to five neighborhood integer pixels, which are lined up in the horizontal direction and located immediately below the FP, is given to each of the FPs at the (¼, ¾) pixel positions shown with horizontal hatching. A pixel value obtained by applying a one-dimensional low-pass filter with coefficients of ( 3/32, 13/32, 13/32, 3/32) to four neighborhood integer pixels, which are lined up in the horizontal direction and located immediately below the FP, is given to each of the FPs in the (¾, ¾) pixel positions shown with lattice-form hatching. 
     The motion vector generation unit  34  generates motion vectors from a processing target block of the coding target frame to positions where block matching for the motion compensation is performed in predetermined regions in the first or second prediction reference images, and outputs these motion vectors to the reference region selector  36  and predicted image production unit  38 . For example, the motion vector generation unit  34  generates motion vectors from (−16, −16) to (16, 16) centered on the same position as the processing target block of the coding target frame. 
     The reference region selector  36  acquires MVDs in the blocks surrounding the processing target block from the MVD storage unit  20 , and uses the absolute values of these MVDs as complexity information that indicates the degree of complexity of the movement of the processing target block. Since the MVD is a differential vector between the motion vector for a certain block and the motion vectors for blocks surrounding the certain block, the absolute value of MVDs of blocks surrounding the processing target block with complex movement is large. On the other hand, the absolute value of MVDs of blocks surrounding the processing target block with flat movement is small. Accordingly, the complexity of the movement of the processing target block from the reference frame can be expressed by the absolute value of the MVDs of blocks surrounding the processing target block. 
     In cases where the absolute values of the MVDs in blocks surrounding the processing target blocks is smaller than a predetermined value, the reference region selector  36  decides that the movement of the processing target block is not complex, and then decides that the first prediction reference image stored in the first prediction reference region storage unit  30  should be selected as the prediction reference image used for motion compensation prediction. On the other hand, in cases where the absolute value of the MVDs in blocks surrounding the processing target block is equal to or greater than the predetermined value, the reference region selector  36  decides that the movement of the processing target block is complex, and then decides that the second prediction reference image stored in the second prediction reference region storage unit  32  should be selected as the prediction reference image used for motion compensation prediction. The reference region selector  36  outputs the decision to the predicted image production unit  38 . 
     On the basis of the decision results from the reference region selector  36 , the predicted image production unit  38  selects either the first prediction reference image or second prediction reference image. The predicted image production unit  38  takes the images of blocks of portions specified by the motion vectors output by the motion vector generation unit  34  from the selected image as predicted image candidates, and establishes a correspondence between these candidates and the abovementioned motion vectors. Such predicted image candidates are determined for all of a plurality of motion vectors generated by the motion vector generation unit  34 , so that a plurality of sets, each of which is constituted by the predicted image candidate, and the motion vector corresponding to the candidate are produced. 
     The prediction error decision unit  40  selects the predicted image candidate that shows the least error with respect to the processing target block in the coding target frame EI among the predicted image candidates produced by the predicted image production unit  38 , and takes the selected candidate as the predicted image PI of the processing target block. Furthermore, the prediction error decision unit  40  takes the motion vector that has been associated with the selected candidate as the motion vector of the processing target block. The predicted images PI are determined for all of the blocks of the coding target frame EI. These predicted images are processed as described above by the subtraction unit  6 . Furthermore, motion vectors are also determined for all of the blocks of the coding target frame EI, and these motion vectors are converted into MVDs by the prediction error decision unit  40 . Such MVDs are output to the encoding unit  12  by the prediction error decision unit  40 . 
     Next, the operation of the video encoding apparatus  1  will be described. At the same time, a video encoding method of a first embodiment of the present invention will be described.  FIG. 5  is a flow chart which shows a video encoding method of a first embodiment. Furthermore,  FIG. 6  is a flow chart relating to motion compensation prediction in this video encoding method. 
     In the video encoding method of the first embodiment, as shown in  FIG. 5 , motion compensation prediction is first performed by the motion compensation prediction unit  2  (step S 01 ). In the motion compensation prediction, as shown in  FIG. 6 , prediction reference image is first produced by the prediction reference region production unit  24  (step S 02 ). The prediction reference image is produced on the basis of the reference frame. The reference frame is converted into an image with a quadrupled resolution by the ½ pixel interpolation region production unit  42  and ¼ pixel interpolation region production unit  44 , and the resulting image with a quadrupled resolution is taken as prediction reference image. 
     As described above, the prediction reference image is converted into the first prediction reference image by the first FP production unit  26 , and is stored in the first prediction reference region storage unit  30 . Furthermore, the prediction reference image is converted into the second prediction reference image by the second FP production unit  28 , and is stored in the second prediction reference region storage unit  32  (step S 03 ). 
     Next, the degree of complexity of the processing target block is determined by the reference region selector  36  using the MVDs of blocks surrounding the processing target block. This degree of complexity is compared with the predetermined value by the reference region selector  36 , and a decision that selects either the first prediction reference image or second prediction reference image is made on the basis of the results of this comparison (step S 04 ). 
     Next, the motion vector is generated by the motion vector generation unit  34 , and the motion vector is output to the predicted image production unit  38  (step S 05 ). Then, on the basis of the degree of complexity of the movement of the processing target block, the first prediction reference image or the second prediction reference image is selected by the reference region selector  36 . Image of the region specified by the abovementioned motion vector in the image selected by the reference region selector  36  is extracted by the predicted image production unit  38 , and is taken as predicted image candidate. The predicted image candidate is associated with the motion vector (step S 06 ). 
     The processing of step S 05  and step S 06  is repeated for a region in the prediction reference image which is predetermined for the processing target block, and the candidate showing the least error with respect to the processing target block among the plurality of predicted image candidates is extracted by the prediction error decision unit  40  as the predicted image of the processing target block. Furthermore, the motion vector that is associated with the predicted image candidate thus extracted is extracted by the prediction error decision unit  40  as the motion vector of the processing target block (step S 07 ). After the processing of steps S 02  through S 07  has been repeated for all of the blocks of the coding target frame, predicted images of the coding target frame are produced and output to the subtraction unit  6 ; furthermore, motion vectors of all of the blocks are converted into MVDs, and these MVDs are output to the encoding unit  12 . 
     Returning to  FIG. 5 , calculation of the differences between the predicted images output by the motion compensation prediction unit  2  and the coding target frame is performed by the subtraction unit  6  so that predicted residual image is produced (step S 08 ). The predicted residual image is decomposed into a set of coefficients by the conversion unit  8  (step S 09 ). The coefficients are respectively quantized by the quantizing unit  10 , and are thus converted into quantized coefficients (step S 10 ). Then, the abovementioned MVD and the quantized coefficients are encoded by the encoding unit  12 , so that compressed data is produced (step S 11 ). 
     Next, a video encoding program  50  that causes a computer to function as the video encoding apparatus  1  will be described.  FIG. 7  is a block diagram which illustrates the configuration of the video encoding program  50 . The video encoding program  50  comprises a main module  51  that controls the processing, a motion compensation prediction module  52 , a subtraction module  54 , a conversion module  56 , a quantizing module  58 , an encoding module  60 , an inverse quantizing module  62 , an inverse conversion module  64 , an addition module  66 , and an MVD memory module  68 . As is shown in  FIG. 8 , which is a diagram that illustrates the configuration of the motion compensation prediction module  52 , the motion compensation prediction module  52  comprises a prediction reference region production sub-module  70 , a first FP production sub-module  72 , a second FP production sub-module  74 , a motion vector generation sub-module  76 , a reference region selection sub-module  78 , a predicted image production sub-module  80 , and a prediction error decision module  82 . The prediction reference region production sub-module  70  comprises a ½ pixel interpolation region production sub-module  84  and a ¼ pixel interpolation region production sub-module  86 . 
     The functions that are realized in a computer by the motion compensation prediction module  52 , subtraction module  54 , conversion module  56 , quantizing module  58 , encoding module  60 , inverse quantizing module  62 , inverse conversion module  64 , addition module  66 , MVD memory module  68 , prediction reference region production sub-module  70 , first FP production sub-module  72 , second FP production sub-module  74 , motion vector generation sub-module  76 , reference region selection sub-module  78 , predicted image production sub-module  80 , prediction error decision module  82 ,  1 / 2  pixel interpolation region production sub-module  84 , and ¼ pixel interpolation region production sub-module  86  are respectively the same as the motion compensation prediction unit  2 , subtraction unit  6 , conversion unit  8 , quantizing unit  10 , encoding unit  12 , inverse quantizing unit  14 , inverse conversion unit  16 , addition unit  18 , MVD storage unit  20 , prediction reference region production unit  24 , first FP production unit  26 , second FP production unit  28 , motion vector generation unit  34 , reference region selector  36 , predicted image production unit  38 , prediction error decision unit  40 , ½ pixel interpolation region production unit  42 , and ¼ pixel interpolation region production unit  44 . The video encoding program  50  is provided, for example, by recording media such as CD-ROM, DVD, ROM, or by semiconductor memories. The video encoding program  50  may be a program provided as computer data signals over a carrier wave through a network. 
     The action and effect of the video encoding apparatus  1  of the first embodiment will be described below. In the video encoding apparatus  1 , the absolute values of MVDs surrounding blocks are extracted for each of a plurality of blocks into which the coding target frame is divided. The absolute values of these MVD express the degree of complexity of the movement from the reference frame for the processing target block. In the video encoding apparatus  1 , in cases where the absolute values of the MVDs in blocks surrounding the processing target block are smaller than a predetermined value, the predicted image is produced using the first prediction reference image produced by the first FP production unit  26 . Namely, in cases where the movement of the processing target block from the reference frame is not complex, the predicted image is extracted from the first prediction reference image in which the number of FPs is small. Accordingly, for the processing target block in which the movement from the reference frame is not complex, the encoding efficiency is improved by increasing the resolution. On the other hand, in cases where the absolute values of the MVDs in blocks surrounding the processing target are equal to or greater than the predetermined value, the predicted image is produced using the second prediction reference image produced by the second FP production unit  28 . Namely, in cases where the movement of the processing target block is complex, the predicted image is extracted from the second prediction reference image in which the number of FPs is large. Accordingly, for the processing target block in which the movement from the reference frame is complex, since the difference between the predicted image and the image of the processing target block is small as a result of the predicted image being extracted from second prediction reference image in which the number of FPs is large, the redundancy is reduced. Thus, as a result of predicted images being produced from first prediction reference image and second prediction reference image in a flexible manner in accordance with variation of the processing target block from the reference frame, the encoding efficiency is improved. 
     Note that, in the abovementioned motion compensation prediction unit  2 , the prediction reference image for the reference frame as a whole is produced when motion compensation prediction is performed. However, it would also be possible to produce prediction reference image only for a predetermined region in the reference frame in accordance with the positions of the processing target blocks, i.e., region in which block matching is to be performed in order to detect motion vector. In this case, the prediction reference image is newly produced each time that the processing target block is switched.  FIG. 9  is a diagram which shows the configuration of an alternative motion compensation prediction unit in the video encoding apparatus of the first embodiment. This motion compensation prediction unit  88  can be substituted for the motion compensation prediction unit  2  of the video encoding apparatus  1 . 
     As is shown in  FIG. 9 , the motion compensation prediction unit  88  comprises a prediction reference region production unit  90 , an adaptive FP production unit  92 , a prediction reference region storage unit  94 , a motion vector generation unit  96 , a predicted image production unit  98 , and a prediction error decision unit  100 . 
     The prediction reference region production unit  90  produces a prediction reference image on the basis of image of a predetermined region in the reference frame corresponding to the processing target block in which motion compensation prediction is to be performed. Such a predetermined region is a region in which block matching is to be performed in order to detect the motion vector of the processing target block. 
     The prediction reference region production unit  90  comprises a ½ pixel interpolation region production unit  102  and a ¼ pixel interpolation region production unit  104 . The ½ pixel interpolation region production unit  102  converts the image of the abovementioned predetermined region in the reference frame into an image with a doubled resolution. Furthermore, the ¼ pixel interpolation region production unit produces a prediction reference image in which the image with a doubled resolution is further converted into an image with a quadrupled resolution. The abovementioned increase in resolution is realized by processing that is the same as the processing performed by the above-mentioned ½ pixel interpolation region production unit  42  and ¼ pixel interpolation region production unit  44 . 
     The adaptive FP production unit  92  acquires MVDs in blocks surrounding the processing target block from the MVD storage unit  20 . In cases where the absolute values of the MVD are smaller than a predetermined value, the adaptive FP production unit  92  converts the (¾, ¾) pixel positions of the prediction reference image as FPs. The production processing of such FPs is the same as the processing performed by the first FP production unit  26 . On the other hand, in cases where the absolute values of the abovementioned MVD are equal to or greater than the predetermined value, the adaptive FP production unit  92  provides FP to the prediction reference image by the same processing as that of the second FP production unit  28 . The prediction reference image provided with FPs by the adaptive FP production unit  92  is stored in the prediction reference region storage unit  94 . 
     The motion vector generation unit  96  generates motion vectors from the processing target block to the positions of the prediction reference image for which matching is to be performed, and outputs these motion vectors to the predicted image production unit  98 . The motion vectors are generated to realize block matching with the entire region of prediction reference image. 
     The predicted image production unit  98  extracts an image of a region which is specified by the motion vector output by the motion vector generation unit  96  among the prediction reference images stored in the prediction reference region storage unit  94 , as a candidate for the predicted image, and establishes a correspondence between the predicted image candidate and the motion vector. Such a predicted image candidate is produced in correspondence with each of the motion vectors generated by the motion vector generation unit  96 . 
     The prediction error decision unit  100  selects the predicted image candidate that shows the least error with respect to the processing target block among the predicted images candidates produced by the predicted image production unit  98 , and takes the selected candidates as the predicted image PI of the processing target block. Furthermore, the prediction error decision unit  100  takes the motion vector that is associated with the selected predicted image candidate as the motion vector of the processing target block. The predicted images are determined for all of the blocks of the coding target frame EI, and these predicted images PI are then output to the subtraction unit  6 . Furthermore, motion vectors are also determined for all of the blocks of the coding target frame EI. These motion vectors are converted into MVDs, and then the MVDs output to the encoding unit  12  by the prediction error decision unit  100 . 
     The operation of the video encoding apparatus  1  in a case where the motion compensation prediction unit  88  is used, and the video encoding method performed by this video encoding apparatus  1 , will be described below. Here, only the processing performed by the motion compensation prediction unit  88  that differs from the processing performed by the video encoding apparatus  1  using the motion compensation prediction unit  2  will be described.  FIG. 10  is a flow chart relating to alternative motion compensation prediction in the video encoding method of the first embodiment. 
     In this video encoding method, an image of a predetermined region of the reference frame is first extracted in accordance with the positions of the processing target block. The extracted image is converted into an image with a quadrupled resolution by the prediction reference region production unit  90 . The image with a quadrupled resolution is taken as the prediction reference image (step S 20 ). 
     Next, FPs are provided in the prediction reference image by the adaptive FP production unit  92  (step S 21 ). The adaptive FP production unit  92  changes the number of FP provided in the prediction reference image as described above on the basis of the results of a comparison of the absolute values of the MVDs of the blocks surrounding the processing target block with a predetermined value. The prediction reference image thus provided with FPs is stored in the prediction reference region storage unit  94 . 
     Next, the motion vector generated by the motion vector generation unit  96  is output to the predicted image production unit  98  (step S 22 ). Furthermore, an image of the block specified by the motion vector is extracted from the prediction reference image by the predicted image production unit  98 , and the extracted image is taken as a predicted image candidate and associated with the motion vector (step S 23 ). The processing of steps S 22  and S 23  is repeated while the motion vectors are changed, so that a plurality of predicted image candidates are produced. Furthermore, the candidate showing the least error with respect to the processing target block, among the plurality of predicted image candidates, is selected by the prediction error decision unit  40  as the predicted image of the processing target block. Moreover, the motion vector associated with the selected candidate is extracted as the motion vector of the processing target block by the prediction error decision unit  100  (step S 24 ). The processing of steps S 20  through S 24  is repeated for all of the blocks of the coding target frame so that predicted images of the coding target frame are produced, and these predicted images are output to the subtraction unit  6 . Furthermore, motion vectors relating to all of the blocks are converted into MVDs by the prediction error decision unit  100 , and the MVDs are then output to the encoding unit  12 . 
     Next, a video encoding program which is used to cause a computer to function as the video encoding apparatus  1 , comprising the motion compensation prediction unit  88 , will be described. This video encoding program is constructed by replacing the motion compensation prediction module  52  in the video encoding program  50  with the motion compensation prediction module  106  described below.  FIG. 11  is a diagram which shows the configuration of an alternative motion compensation prediction module in the video encoding program of the first embodiment. 
     The motion compensation prediction module  106  comprises a prediction reference region production sub-module  108 , an adaptive FP production sub-module  110 , a motion vector generation sub-module  112 , a predicted image production sub-module  114 , and a prediction error decision sub-module  116 . Furthermore, the prediction reference region production sub-module  108  comprises a ½ pixel interpolation region production sub-module  118  and a ¼ pixel interpolation region production sub-module  120 . The functions that are realized in a computer by the prediction reference region production sub-module  108 , adaptive production sub-module  110 , motion vector generation sub-module  112 , predicted image production sub-module  114 , prediction error decision sub-module  116 , ½ pixel interpolation region production sub-module  118 , and ¼ pixel interpolation region production sub-module  120  are respectively the same as the prediction reference production unit  90 , adaptive FP production unit  92 , motion vector generation unit  96 , predicted image production unit  98 , prediction error decision unit  100 , ½ pixel interpolation region production unit  102 , and ¼ pixel interpolation region production unit  104 . 
     In the case of processing that thus produces the prediction reference image for a predetermined region in the reference frame for which block matching is to be performed, the memory capacity required at one time is reduced compared to processing that produces the prediction reference image for the reference frames as a whole. 
     Second Embodiment 
     Next, a video encoding apparatus  130  of a second embodiment of the present invention will be described. The video encoding apparatus  130  differs from the video encoding apparatus  1  of the first embodiment in that the numbers of non-zero DCT coefficients in the blocks surrounding the processing target block are used to express the degree of complexity of the movement of the processing target block from the reference frame. Since the DCT coefficients are coefficients into which the prediction residual difference image is decomposed, the number of non-zero DCT coefficients increases with an increase in the difference between the processing target block and the predicted image, i.e., with an increase in the degree of complexity of the movement of the processing target block from the reference frame. 
     In physical terms, the video encoding apparatus  130  has a configuration similar to that of the video encoding apparatus  1  of the first embodiment.  FIG. 12  is a block diagram which shows the functional configuration of a video encoding apparatus of a second embodiment. In functional terms, as is shown in  FIG. 12 , the video encoding apparatus  130  comprises a motion compensation prediction unit  132 , a frame memory  134 , a 20 subtraction unit  136 , a conversion unit  138 , a quantizing unit  140 , an encoding unit  142 , an inverse quantizing unit  144 , an inverse conversion unit  146 , an addition unit  148 , and a coefficient number storage unit  150 . Among these constituent elements, the motion compensation prediction unit  132 , conversion unit  138 , and coefficient number storage unit  150  are units with 47 functions that differ from those in the video encoding apparatus  1 . The motion compensation prediction unit  132 , conversion unit  138 , and coefficient number storage unit  150  will be described below, and a description of the other units will be omitted. 
     The conversion unit  138  divides the prediction residual difference image output from the subtraction unit  136  into a plurality of blocks of a predetermined size, and performs a DCT on the prediction residual difference image in each of the plurality of blocks. The DCT coefficients are quantized by the quantizing unit  140  and are thus converted into quantized DCT coefficients, and the number of non-zero quantized DCT coefficients is recorded in the coefficient number storage unit for each block. These numbers of non-zero DCT coefficients stored in the coefficient number storage unit  150  are used by the motion compensation prediction unit  132 . 
     The motion compensation prediction unit  132  has a configuration similar to that of the motion compensation prediction unit  2  of the first embodiment shown in  FIG. 2 , but uses the numbers of non-zero quantized DCT coefficients in the blocks surrounding the processing target block instead of using the absolute values of the MVDs in the blocks surrounding the processing target block when the reference region selector  36  determines the degree of complexity of the movement in the processing target block in the first embodiment. Furthermore, since the remaining processing of the motion compensation prediction unit  132  is similar to that of the motion compensation prediction unit  2 , a description of this processing is omitted. 
     The operation of the video encoding apparatus  130  and the video encoding method performed by the video encoding apparatus  130  also differ from the first embodiment only in that the numbers of non-zero quantized DCT coefficients in the blocks surrounding the processing target block are used to express the degree of complexity of the movement of the processing target block from the reference frame. Accordingly, a description of this operation and method is omitted. Furthermore, the video encoding program that is used to cause a computer to operate as the video encoding apparatus  130  similarly differs from the video encoding program  50  of the first embodiment only in that the numbers of non-zero quantized DCT coefficients in the surrounding blocks are used to express the degree of complexity of the movement of the processing target block from the reference frame. Accordingly, a description of this program is omitted. 
     Furthermore, in the video encoding apparatus  130  as in the video encoding apparatus  1  of the first embodiment, the prediction reference image may be produced for the reference frame as a whole when motion compensation prediction is performed, or the prediction reference image may be produced only for a predetermined region in the reference frame for which block matching is to be performed in accordance with the position of the processing target block. 
     As explained above, the concept of the present invention can also be realized by using the numbers of non-zero quantized DCT coefficients in the blocks surrounding the processing target block as the degree of complexity of the movement of the processing target block from the reference frames as described above. 
     Third Embodiment 
     Next, a video encoding apparatus  160  of a third embodiment of the present invention will be described. The video encoding apparatus  160  differs from the video encoding apparatus  1  of the first embodiment in that the absolute value of the MVD in the processing target block is used to express the degree of complexity of the movement of the processing target block from the reference frame. 
     In physical terms, the video encoding apparatus  160  has a configuration similar to that of the video encoding apparatus  1  of the first embodiment.  FIG. 13  is a block diagram which shows the functional configuration of a video encoding apparatus constituting a third embodiment. In functional terms, as is shown  FIG. 13 , the video encoding apparatus  160  comprises a motion compensation prediction unit  162 , a frame memory  164 , a subtraction unit  166 , a conversion unit  168 , a quantizing unit  170 , an encoding unit  172 , an inverse quantizing unit  174 , an inverse conversion unit  176 , and an addition unit  178 . Among these constituent elements, in the video encoding apparatus  160 , the motion compensation prediction unit  162  performs processing that differs from that of the constituent elements provided in the video encoding apparatus  1 . Accordingly, the motion compensation prediction unit  162  will be described below, and a description relating to the other constituent elements will be omitted. 
       FIG. 14  is a block diagram which shows the configuration of the motion compensation prediction unit of the video encoding apparatus of the third embodiment. As shown in  FIG. 14 , the motion compensation prediction unit  162  comprises a prediction reference region production unit  180 , a prediction reference region storage unit  182 , a motion vector generation unit  184 , and adaptive FP production unit  186 , a predicted image production unit  188 , and a prediction error decision unit  190 . 
     The prediction reference region production unit  180  comprises a ½ pixel interpolation region production unit  192  and a ¼ pixel interpolation region production unit  194 . The prediction reference region production unit  180  produces a prediction reference image in which an image of predetermined region of the reference frame corresponding to the processing target block is converted into an image with a quadrupled resolution by the same processing as that of the prediction reference region production unit  90  of the first embodiment. The prediction reference region production unit  180  stores the prediction reference image in the prediction reference region storage unit  182 . 
     The motion vector generation unit  184  produces motion vectors to the positions in the prediction reference image in which block matching is to be performed for the processing target block, and outputs these motion vectors to the adaptive FP production unit  186  and predicted image production unit  188 . 
     The adaptive FP production unit  186  produces MVD by calculating a difference between median value of the motion vectors in the blocks surrounding the processing target block and a motion vector output by the motion vector generation unit  184 . In cases where the absolute value of the MVD is smaller than a predetermined value, the adaptive FP production unit  186  converts the (¾, ¾) position pixels of the prediction reference image into the FPs. The processing that produces these FPs is similar to the processing performed by the first FP production unit  26  of the first embodiment. On the other hand, in cases where the absolute value of the MVD is equal to or greater than the predetermined value, FP are provided in the prediction reference image by processing similar to that of the second FP production unit of the first embodiment. The prediction reference image provided with FP by the adaptive FP production unit  186  is output to the predicted image production unit  188 . 
     The predicted image production unit  188  takes the image of a region specified by the motion vector output by the motion vector generation unit  184  from the prediction reference image output by the adaptive FP production unit  186  as a predicted image candidate, and establishes a correspondence between the predicted image candidate and the motion vector. The motion vector generation unit  184  produces a plurality of motion vectors so that block matching is performed for the entire region of the prediction reference image, and the predicted image candidates for the plurality of motion vectors are produced by the predicted image production unit  188 . 
     The prediction error decision unit  190  selects the candidate that shows the least error with respect to the processing target block, among the plurality of predicted image candidates produced by the predicted image production unit  188 , as a predicted image. The prediction error decision unit  190  extracts the motion vector associated with the selected candidate as the motion vector of the processing target block. Predicted images are determined for all of the blocks of the coding target frame, and are output to the subtraction unit  166 . Motion vectors are also determined for all of the blocks of the coding target frame. These motion vectors are converted into MVDs, and the MVDs are then output to the encoding unit  172  by the prediction error decision unit  190 . 
     Next, the operation of the video encoding apparatus  160  and the video encoding method of the third embodiment will be described. Here, only the processing relating to the motion compensation prediction that differs from the video encoding method of the first embodiment will be described.  FIG. 15  is a flow chart which shows the processing of the motion compensation prediction in the third embodiment. 
     In the motion compensation prediction of the third embodiment, as shown in  FIG. 15 , an image of a region which is predetermined in accordance with the processing target block, among the reference frame, is first converted into an image with a quadrupled resolution by the prediction reference region production unit  180 , and the image with a quadrupled resolution is stored as a prediction reference image in the prediction reference region storage unit  182  (step S 30 ). 
     Next, a motion vector to a position of the prediction reference image in which block matching is to be performed is generated by the motion vector generation unit  184 , and the motion vectors is output to the adaptive FP production unit  186  and predicted image production unit  188  (step S 31 ). 
     Next, a differential motion vector (MVD) is produced by the adaptive FP production unit  186  on the basis of the motion vector output by the motion vector generation unit  184  and vectors formed by the median value of motion vectors of the blocks surrounding the processing target block. The adaptive FP production unit  186  varies the number of FP provided in the prediction reference image as described above on the basis of the result of a comparison of the absolute value of the MVD and a predetermined value (step S 33 ). 
     The image of the block in positions corresponding to the motion vector output by the motion vector generation unit  184  is extracted by the predicted image production unit  188  from the prediction reference image output by the adaptive FP production unit  186 , and the image is taken as a predicted image candidate, caused to correspond to the abovementioned motion vector and output to the prediction error decision unit  190  (step S 34 ). The processing from step S 31  to step S 34  is repeated until block matching has been performed for all of the entire region of the prediction reference image, so that a plurality of predicted image candidates is produced. 
     The prediction error decision unit  190  selects the candidate that shows the least error with respect to the processing target block, among the plurality of predicted image candidates, as a predicted image, and outputs the predicted image to the subtraction unit  166 . Furthermore, the prediction error decision unit  190  extracts the motion vector that is associated with the predicted image. The prediction error decision unit  190  converts the motion vectors into MVD, and outputs the MVD to the encoding unit  172  (step S 35 ) 
     The video encoding program that causes a computer to function as the video encoding apparatus  160  will be described below. Since this video encoding program differs from the video encoding program  50  of the first embodiment only in terms of the configuration of the motion compensation prediction module, only the configuration of the motion compensation prediction module  200  will be described here. 
       FIG. 16  is a diagram which shows the configuration of the motion compensation prediction module of a video encoding program relating to a third embodiment. The motion compensation prediction module  200  comprises a prediction reference region production sub-module  202 , a motion vector generation sub-module  204 , an adaptive production sub-module  206 , a predicted image production sub-module  208 , and a prediction error decision sub-module  210 . The prediction reference region production sub-module  202  comprises a ½ pixel interpolation region production sub-module  212  and a ¼ pixel interpolation region production sub-module  214 . The functions that are realized in a computer by the prediction reference region production sub-module  202 , motion vector generation sub-module  204 , adaptive production sub-module  206 , predicted image production sub-module  208 , prediction error decision sub-module  210 , ½ pixel interpolation region production sub-module  212 , and ¼ pixel interpolation region production sub-module  214  are respectively the same as the prediction reference region production unit  180 , motion vector generation unit  184 , adaptive FP production unit  186 , predicted image production unit  188 , prediction error decision unit  190 , ½ pixel interpolation region production unit  192 , and ¼ pixel interpolation region production unit  194 . 
     As explained above, the concept of the present invention can also be realized by means of a video encoding apparatus with a configuration that uses the MVD of the processing target block themselves for expressing the degree of complexity of the movement of the processing target block. 
     Fourth Embodiment 
     Next, a video decoding apparatus  220  of a fourth embodiment of the present invention will be described. The video decoding apparatus  220  is an apparatus that produces video by decoding compressed data produced by the video encoding apparatus  1  of the first embodiment. In physical terms, the video decoding apparatus  220  is a computer comprising a CPU (central processing unit), a memory apparatus called a memory, a storage apparatus called a hard disk, and the like. Here, in addition to ordinary computers, such as personal computers or the like, the term “computer” also includes portable information terminals, such as mobile communications terminals, so that the concept of the present invention can be widely applied to apparatus that is capable of information processing. 
     The functional configuration of the video decoding apparatus  220  will be described below.  FIG. 17  is a block diagram which shows the functional configuration of a video decoding apparatus relating to a fourth embodiment. In functional terms, the video decoding apparatus  220  comprises a decoding unit  222 , an inverse quantizing unit  224 , an inverse conversion unit  226 , an MVD storage unit  228 , a motion compensation prediction unit  230 , a frame memory  232 , and an addition unit  234 . 
     The decoding unit  222  is a unit that decodes compressed data produced by the video encoding apparatus  1 . The decoding unit outputs the MVDs obtained by decoding the compressed data to the MVD storage unit  228  and the motion compensation prediction unit  230 . Furthermore, the decoding unit  222  outputs the quantized coefficients decoded from the compressed data to the inverse quantizing unit  224 . 
     The inverse quantizing unit  224  produces coefficients by performing an inverse quantizing operation on the quantized coefficients, and outputs these coefficients to the inverse conversion unit  226 . Using the coefficients output by the inverse quantizing unit  224 , the inverse conversion unit  226  produces a predicted residual difference image by performing an inverse conversion on the basis of a predetermined inverse conversion rule. The inverse conversion unit  226  outputs the predicted residual image to the addition unit  234 . Here, in cases where the DCT is used by the conversion unit  8  of the video encoding apparatus  1 , the inverse DCT can be used as the specified inverse conversion rule. Furthermore, in cases where the MP method is used by the conversion unit  8  of the video encoding apparatus  1 , the inverse operation of the MP method can be used as the predetermined inverse conversion rule. 
     The MVD storage unit  228  stores the MVDs that are output by the decoding unit  222 . The MVDs stored by the MVD storage unit are utilized by the motion compensation prediction unit  230 . 
     Using the MVDs output by the decoding unit  222 , the motion compensation prediction unit  230  produces a predicted image of the decoding target frame from the reference frame stored in the frame memory  232 . The details of this processing will be described later. The motion compensation prediction unit  230  outputs the predicted image that is produced to the addition unit  234 . 
     The addition unit  234  adds the predicted image output by the motion compensation prediction unit  230  and the predicted residual difference image output by the inverse conversion unit  226 , and thus produces the decoding target frame. The addition unit  234  outputs the frame to the frame memory  232 , and the frame that is output to the frame memory  232  is utilized by the motion compensation prediction unit  230  as a reference frame. 
     Next, the details of the motion compensation prediction unit  230  will be described.  FIG. 18  is a block diagram which shows the configuration of the motion compensation prediction unit of the video decoding apparatus of the fourth embodiment. The motion compensation prediction unit  230  comprises a prediction reference region production unit  236 , a first FP production unit  238 , a second FP production unit  240 , a first prediction reference region storage unit  242 , a second prediction reference region storage unit  244 , a reference region selector  246 , and a predicted image production unit  248 . 
     The prediction reference region production unit  236  produces a prediction reference image on the basis of the reference frame RI stored in the frame memory  232 . The prediction reference region production unit  24  has a ½ pixel interpolation region production unit  250  and a ¼ pixel interpolation region production unit  252 . The ½ pixel interpolation region production unit  250  and ¼ pixel interpolation region production unit  252  respectively perform the same processing as the ½ pixel interpolation region production unit  42  and ¼ pixel interpolation region production unit  44  of the video encoding apparatus  1 . 
     The first FP production unit  238  performs the same processing as the first FP production unit  26  of the video encoding apparatus  1 ; this unit produces a first prediction reference image, and stores the image in the first prediction reference region storage unit  242 . The second FP production unit  240  performs the same processing as the second FP production unit  28  of the video encoding apparatus  1 ; this unit produces a second prediction reference image, and stores the image in the second prediction reference region storage unit  244 . 
     The reference region selector  246  performs the same processing as the reference region selector  36  of the video encoding apparatus  1 ; this selector acquires MVDs in the blocks surrounding the processing target block from the MVD storage unit  228 , compares the absolute values of the acquired MVDs with a predetermined value, and outputs the decision that selects either the first prediction reference image or the second prediction reference image on the basis of the result of the comparison. 
     The predicted image production unit  248  calculates the motion vector of the processing target block from the MVD output by the decoding unit  222 . Furthermore, the predicted image production unit  248  selects either the first prediction reference image or the second prediction reference images on the basis of the decision produced by the reference region selector  246 , and extracts an image of a region specified by the motion vector of the processing target block, among the selected image, as a predicted image of the processing target block. 
     The operation of the video decoding apparatus  220  will be described below, and the video decoding method of the fourth embodiment will also be described.  FIG. 19  is a flow chart of a video decoding method relating to a fourth embodiment. Furthermore,  FIG. 20  is a flow chart showing processing relating to the motion compensation prediction of the video decoding method of the fourth embodiment. 
     In the video decoding method of the fourth embodiment, as shown in  FIG. 19 , the MVDs and quantized coefficients for each of the plurality of blocks of the decoding target frame are first decoded by the decoding unit  222  from the compressed data produced by the video encoding apparatus  1  (step S 40 ). The quantized coefficients are converted into coefficients produced by the performance of an inverse quantizing operation by the inverse quantizing unit  224  (step S 41 ). These coefficients are used for the inverse conversion performed by the inverse conversion unit  226 , and as a result of this inverse conversion, the predicted residual difference image is restored (step S 42 ). 
     The MVDs decoded by the decoding unit  222  are stored by the MVD storage unit  208 . Furthermore, the MVDs decoded by the decoding unit  222  are output to the motion compensation prediction unit  230 , and motion compensation prediction is performed by the motion compensation prediction unit  230  using these MVDs (step S 43 ). 
     In the motion compensation prediction unit  230 , as shown in  FIG. 20 , a prediction reference image, which is formed as an image in which the resolution of the reference frame is quadrupled is produced by the prediction reference region production unit  236  (step S 44 ). The prediction reference image is output to the first FP production unit and second FP production unit  240 . The prediction reference image is converted into a first prediction reference image by the first FP production unit  238 , or is converted into a second prediction reference image by the second FP production unit  240  (step S 45 ). 
     Next, the degree of complexity of the movement of the processing target block is determined by the reference region selector  246  using the MVDs in the blocks surrounding the processing target block. This degree of complexity is compared with a predetermined value by the reference region selector  246 , and a decision that selects either the first prediction reference image or the second prediction reference image is made on the basis of the results of the comparison (step S 46 ). Furthermore, a motion vector of the processing target block is generated on the basis of the MVD by the predicted image production unit  248 . Moreover, an image of a region specified by the motion vector of the processing target block is extracted by the predicted image production unit  248  from the image selected by the reference region selector  246 , among the first prediction reference images and second prediction reference images (step S 47 ). The image extracted by the predicted image production unit  248  is taken as the predicted image of the processing target block. 
     The processing of steps S 52  and S 53  is performed for all of the blocks of the decoding target frame, so that the predicted images of the decoding target frame are produced. Returning to  FIG. 19 , the predicted images of the decoding target frame and the predicted residual difference image are added by the adding unit  234 , so that the decoding target frame is restored (step S 48 ). 
     The video decoding program that causes a computer to operate as the video decoding apparatus  220  will be described below.  FIG. 21  is a diagram which shows the configuration of a video decoding program relating to a fourth embodiment. The video decoding program  260  comprises  260  a main module  261  that controls the processing, a decoding module  262 , an inverse quantizing module  264 , an inverse conversion module  266 , an MVD memory module  268 , a motion compensation prediction module  270 , and an addition module  272 . The motion compensation prediction module  270  comprises a prediction reference region production sub-module  274 , a first FP production sub-module  276 , a second FP production sub-module  278 , a reference region selection sub-module  280 , and a predicted image production sub-module  282 . The prediction reference region production sub-module  274  comprises a ½ pixel interpolation region production sub-module  284  and a ¼ pixel interpolation region production sub-module  286 . 
     The functions that are realized in a computer by the decoding module  262 , inverse quantizing module  264 , inverse conversion module  266 , MVD storage module  268 , motion compensation prediction module  270 , addition module  272 , prediction reference region production sub-module  274 , first FP production sub-module  276 , second FP production sub-module  278 , reference region selection sub-module  280 , predicted image production module  282 , ½ pixel interpolation region production sub-module  284 , and ¼ pixel interpolation region production sub-module  286  are respectively the same as the decoding unit  222 , inverse quantizing unit  224 , inverse conversion unit  226 , MVD storage unit  228 , motion compensation prediction unit  230 , addition unit  234 , prediction reference region production unit  236 , first FP production unit  238 , second FP production unit  240 , reference region selector  246 , predicted image production unit  248 , ½ pixel interpolation region production unit  250 , and ¼ pixel interpolation region production unit  252 . The video decoding program  260  comprises  260  is provided, for example, by recording media such as CD-ROM, DVD, ROM, or by semiconductor memories. The video decoding program  260  comprises  260  may be a program provided as computer data signals over a carrier wave through a network. 
     The action and effect of the video decoding apparatus  220  of the fourth embodiment will be described below. In the video decoding apparatus  220 , the absolute values of MVDs in the blocks surrounding the processing target block are extracted. The absolute values of these MVD express the degree of complexity of the movement of the processing target block from the reference frame. In the video decoding apparatus  220 , in cases where the absolute values of the MVDs in the areas surrounding the processing target block are smaller than a predetermined value, a predicted image is extracted from the first prediction reference image produced by the first FP production unit  238 . Namely, the predicted image is produced by using the first prediction reference image, in which the number of FP is small. On the other hand, in cases where the absolute values of the MVDs in the areas surrounding the processing target block are equal to or greater than the predetermined value, the predicted image is extracted from the second prediction reference image produced by the second FP production unit  240 . Namely, the predicted image is produced by using the second prediction reference image, in which the number of FP is large. Thus, the video decoding apparatus  220  can restore the video by faithfully performing the processing that is the inverse processing with respect to the processing of the video encoding apparatus  1 . 
     Note that, in the motion compensation prediction unit  230 , the prediction reference image is produced for the reference frame as a whole when motion compensation prediction is performed. However, the motion compensation prediction unit  230  may also be constructed so that the prediction reference image is produced only for a predetermined region of the reference frame with respect to the processing target block, i.e., for the region that is required in order to extract the predicted image using the motion vector. In this case, the prediction reference image is produced each time that the processing target block is switched.  FIG. 22  is a block diagram which shows the configuration of an alternative motion compensation prediction unit in the video decoding apparatus of the fourth embodiment. Such a motion compensation prediction unit  290  can be substituted for the motion compensation prediction unit  230  of the video decoding apparatus  220 . 
     The motion compensation prediction unit  290  comprises a prediction reference region production unit  292 , an adaptive FP production unit  294 , a prediction reference region storage unit  296 , and a predicted image production unit  298 . 
     The prediction reference region production unit  292  produces a prediction reference image on the basis of a predetermined region of the reference frame corresponding to the processing target block. The prediction reference region production unit  292  comprises a ½ pixel interpolation region production unit  302  and a ¼ pixel interpolation region production unit  304 . The ½ pixel interpolation region production unit  302  converts an image of the above-mentioned predetermined region into an image with a doubled resolution. Furthermore, the ¼ pixel interpolation region production unit  304  produces a prediction reference image in which the image with a doubled resolution is further converted into an image with a quadrupled resolution. Such an increase in resolution can be realized by processing similar to that performed by the ½ pixel interpolation region production unit  42  and ¼ pixel interpolation region production unit  44  of the video encoding apparatus  1 . 
     The adaptive FP production unit  294  acquires MVDs in the blocks surrounding the processing target block from the MVD storage unit  208 , and in cases where the absolute values of these MVDs are smaller than a predetermined value, the adaptive FP production unit  294  converts the (¾, ¾) pixel positions of the prediction reference image into FPs. The processing that produces these FPs is similar to the processing performed by the first FP production unit  238 . On the other hand, in cases where the absolute values of the abovementioned MVDs are equal to or greater than the predetermined value, the adaptive FP production unit  294  provides FP to the prediction reference image by processing similar to that of the second FP production unit  240 . The prediction reference image provided with FP by the adaptive FP production unit  294  is stored in the prediction reference region storage unit  296 . 
     The predicted image production unit  298  generates a motion vector for the processing target block from the MVD decoded by the decoding unit  222 . The predicted image production unit  298  extracts an image specified by the motion vector of the processing target block from the prediction reference image stored in the prediction reference region storage unit  94 , and outputs the resulting image as a predicted image. 
     Next, the motion compensation prediction module  310  that is used to cause a computer to operate in the same manner as the motion compensation prediction unit  290  will be described. The motion compensation prediction module  310  is used instead of the motion compensation prediction module  270  of the video decoding program  260 .  FIG. 23  is a diagram which shows the configuration of an alternative motion compensation prediction module in the video decoding program of the fourth embodiment. 
     The motion compensation prediction module comprises a prediction reference region production sub-module  312 , an adaptive production sub-module  314 , and a predicted image production sub-module  316 . The prediction reference region production sub-module  312  comprises a ½ pixel interpolation region production sub-module  318  and a ¼ pixel interpolation region production sub-module  320 . The functions that are realized in a computer by the prediction reference region production sub-module  312 , adaptive production sub-module  314 , predicted image production sub-module  316 , ½ pixel interpolation region production sub-module  318 , and ¼ pixel interpolation region production sub-module  320  are respectively the same as the prediction reference region production unit  292 , adaptive FP production unit  294 , predicted image production unit  298 , ½ pixel interpolation region production unit  302 , and ¼ pixel interpolation region production unit  304 . 
     In the case of the motion compensation prediction unit  290 , the prediction reference image can be produced for only the region that is required in order to extract the predicted image for the processing target block; accordingly, the memory capacity that is required in order to produce the prediction reference image for the reference frame as a whole can be reduced. 
     Fifth Embodiment 
     A video decoding apparatus  330  constituting a fifth embodiment of the present invention will be described. The video decoding apparatus  330  is an apparatus that restores video from the compressed data produced by the video encoding apparatus  130  of the second embodiment. The video decoding apparatus  330  differs from the video decoding apparatus  220  of the fourth embodiment in that the numbers of quantized CDT coefficients in the blocks surrounding the processing target block are used to express the degree of complexity of the movement of the processing target block in the decoding target frame from the reference frame. 
     In physical terms, the video decoding apparatus  330  has a configuration similar to that of the video decoding apparatus  220  of the fourth embodiment.  FIG. 24  is a block diagram which shows the functional configuration of a video decoding apparatus relating to a fifth embodiment. In functional terms, the video decoding apparatus  330  comprises a decoding unit  332 , an inverse quantizing unit  334 , an inverse conversion unit  336 , a coefficient number storage unit  338 , a motion compensation prediction unit  340 , a frame memory  342 , and an addition unit  344 . Among these constituent elements, the inverse conversion unit  336 , coefficient number storage unit  338 , and motion compensation prediction unit  340  are units with functions that differ from those of the video decoding apparatus  220 ; accordingly, the inverse conversion unit  336 , coefficient number storage unit  338  and motion compensation prediction unit  340  will be described below, and a description of the other units will be omitted. 
     The inverse conversion unit  336  restores the predicted residual difference image by applying an inverse DCT to the DCT coefficients produced by the performance of an inverse quantizing operation by the inverse quantizing unit  334 . 
     The coefficient number storage unit  338  stores the number of quantized DCT coefficients decoded by the decoding unit  332  for each block of the decoding target frame. The numbers of non-zero quantized DCT coefficients are utilized by the motion compensation prediction unit  340 . 
     In the motion compensation prediction unit  340 , the numbers of the non-zero quantized DCT coefficients in the blocks surrounding the processing target block are used by the reference region selector as the degree of complexity of movement relating to the processing target block. In other respects relating to the configuration of the motion compensation prediction unit  340 , the configuration is the same as that of the motion compensation prediction unit  230  of the video decoding apparatus  220 ; accordingly, a description is omitted. The motion compensation prediction unit  340  produces a predicted image in which the numbers of FP are altered on the basis of this degree of complexity of movement. 
     Furthermore, the video decoding method of the fifth embodiment is the same as the video decoding method of the fourth embodiment, except for the fact that the numbers of non-zero quantized DCT coefficients in the blocks surrounding the processing target block are used as the degree of complexity of the movement of the processing target block; accordingly, a description is omitted. Furthermore, the video decoding program that is used to cause a computer to operate as the video decoding apparatus  330  can also be constructed by changing the motion compensation prediction module  270  of the video decoding program  260  to a module that causes the computer to realize the function of the motion compensation prediction unit  340 . 
     Thus, the video decoding apparatus  330  of the fifth embodiment can restore the video by faithfully performing processing that is the inverse processing with respect to the processing of the video encoding apparatus  130 . 
     Sixth Embodiment 
     A video decoding apparatus  350  of a sixth embodiment of the present invention will be described. The video decoding apparatus  350  is an apparatus that decodes video from the compressed data produced by the video encoding apparatus  160  of the third embodiment. The video decoding apparatus  350  differs from the video decoding apparatus  220  of the fourth embodiment in that the absolute value of the MVD in the processing target block is utilized in order to express the complexity of the movement of the processing target block in the decoding target frame from the reference frame. 
     In physical terms, the video decoding apparatus  350  has a configuration similar to that of the video decoding apparatus  220  of the fourth embodiment.  FIG. 25  is a block diagram which shows the functional configuration of a video decoding apparatus constituting a sixth embodiment. In functional terms, as is shown in  FIG. 25 , the video decoding apparatus  350  comprises a decoding unit  352 , an inverse quantizing unit  354 , an inverse conversion unit  356 , a motion compensation prediction unit  358 , a frame memory  360 , and an addition unit  362 . In the video decoding apparatus  350 , among these constituent elements, the motion compensation prediction unit  358  performs processing that differs from that of the constituent elements provided in the video decoding apparatus  220 ; accordingly, the motion compensation prediction unit  358  will be described below, and a description relating to the other constituent elements will be omitted. 
       FIG. 26  is a block diagram which shows the configuration of the motion compensation prediction unit of the video decoding apparatus of the sixth embodiment. As is shown in  FIG. 26 , the motion compensation prediction unit  358  comprises a prediction reference region production unit  370 , an adaptive FP production unit  372 , a prediction reference region storage unit  374 , and a predicted image production unit  376 . The prediction reference region production unit  370  comprises a ½ pixel interpolation region production unit  380  and a ¼ pixel interpolation region production unit  382 . The prediction reference region production unit  370  produces a prediction reference image in which an image of a predetermined region of the reference frame corresponding to the processing target block are converted into an image with a quadrupled resolution by processing similar to that of the prediction reference region production  292  in the fourth embodiment. 
     In cases where the absolute value of the MVD of the processing target block, which is decoded by the decoding unit  352 , is smaller than a predetermined value, the adaptive FP production unit  372  converts the (¾, ¾) pixel positions of the prediction reference image as FPs. The processing that produces these FPs is similar to the processing performed by the first FP production unit  238  of the fourth embodiment. On the other hand, in cases where the absolute value of the abovementioned MVD is equal to or greater than the predetermined value, the adaptive FP production unit  372  provides FPs to the prediction reference image by processing similar to that of the second FP production unit  240  of the fourth embodiment. The prediction reference image provided by the adaptive FP production unit  372  are stored in the prediction reference region storage unit  374 . 
     The predicted image production unit  376  generates a motion vector from the MVD of the processing target block, which is decoded by the decoding unit  352 . The predicted image production unit  376  takes an image of a region specified by the motion vector of the processing target block, among the prediction reference image produced by the adaptive FP production unit  372 , as a predicted image. The predicted images are determined for all of the blocks of the decoding target frame, and are output to the addition unit  362 . 
     The video decoding method of the sixth embodiment will be described below. In regard to this video decoding method, the motion compensation prediction processing that differs from that of the video decoding method of the fourth embodiment will be described.  FIG. 27  is a flow chart which shows the processing of motion compensation prediction in a video decoding method relating to a sixth embodiment. In this motion compensation prediction processing, as is shown in  FIG. 27 , the prediction reference image is first produced by the prediction reference region production unit  370  (step S 50 ). The prediction reference image is produced on the basis of a predetermined region in the reference frame that is required for producing the predicted image. Next, the absolute value of the MVD of the processing target block is compared with a predetermined value, and the prediction reference image provided with the number of FPs corresponding to the results of this comparison are produced (step S 51 ). Next, a motion vector is produced by the predicted image production unit  376  from the MVD of the processing target block. Then, an image of a region specified by the motion vector of the processing target block is extracted by the predicted image production unit  376 , and the image is output as a predicted image (step S 52 ). The processing of steps S 50  through S 52  is performed for all of the blocks of the decoding target frame, so that the decoding target frames are restored. 
     The video decoding program  390  that is used to cause a computer to operate as the video decoding apparatus  350  will be described below.  FIG. 28  is a diagram which shows the configuration of a video decoding program relating to a sixth embodiment. The video decoding program  390  comprises a main module  391  that generalizes the processing, a decoding module  392 , an inverse quantizing module  394 , an inverse conversion module  396 , a motion compensation prediction module  398 , and an addition module  400 . The motion compensation prediction module  398  comprises a prediction reference region production sub-module  402 , an adaptive production sub-module  404 , and a predicted image production sub-module  406 . The prediction reference region production sub-module  402  comprises a ½ pixel interpolation region production sub-module  408  and a ¼ pixel interpolation region production sub-module  410 . 
     The functions that are realized in a computer by the decoding module  392 , inverse quantizing module  394 , inverse conversion module  396 , motion compensation prediction module  398 , addition module  400 , prediction reference region production sub-module  402 , adaptive production sub-module  404 , predicted image production sub-module  406 , ½ pixel interpolation region production sub-module  408 , and ¼ pixel interpolation region production sub-module  410  are respectively the same as the decoding unit  352 , inverse quantizing unit  354 , inverse conversion unit  356 , motion compensation prediction unit  358 , addition unit  362 , prediction reference region production unit  370 , adaptive FP production unit  372 , predicted image production unit  376 , ½ pixel interpolation region production unit  380 , and ¼ pixel interpolation region production unit  382 . The video decoding program  390  is provided, for example, by recording media such as CD-ROM, DVD, ROM, or by semiconductor memories. The video decoding program  390  may be a program provided as computer data signals over a carrier wave through a network. 
     Thus, the video decoding apparatus  350  of the sixth embodiment can restore the video by faithfully performing the processing that is the inverse processing with respect to the processing of the video encoding apparatus  160 . 
     The principles of the present invention have been illustrated and described in the preferred embodiments, but it is apparent to a person skilled in the art that the present invention can be modified in arrangement and detail without departing from such principles. We, therefore, claim rights to all variations and modifications coming with the spirit and the scope of claims.