JP4580903B2 - Filtering strength determination method, video encoding method, and video decoding method - Google Patents

Description

  The present invention relates to a filtering strength determination method for determining the strength of filtering for removing coding distortion between blocks, and a moving image encoding method for performing coding or decoding of a moving image by filtering according to the determined filtering strength. And a moving picture decoding method.

  Filters are usually used in video compression methods to improve image quality and improve compression ratio. Blocky artifacts typically occur in decoded pictures of low bit rate video compression due to quantization noise and motion compensation. One of the tasks of the filter is to smooth the block boundaries in the decoded picture so that these blocky artifacts are reduced or eliminated.

  For example, video compression methods such as ISO / IEC 14496-2 Part 10 Committee Draft that are currently developing standards use loop filters to improve video compression (eg, Non-patent document 1). This loop filter is applied to both reference and non-reference pictures to improve the picture quality of the decoded picture.

  FIG. 13 shows the decision algorithm used in the committee draft of the ISO / IEC 14496-2 Part 10 standard to select the strength of the filter used.

  The decision to select the strength of the filter used is performed at the block boundary between two adjacent blocks p and q. It is determined whether or not these blocks p or q are intra-picture (Intra) encoded (step S102). Here, when one of the block p and the block q is intra-coded (Yes in step S102), it is determined whether or not the block boundary becomes a macroblock boundary (step S103). As a result of this determination, when the block boundary becomes a macroblock boundary, that is, when two blocks are not included in the same macroblock, the strongest filter strength (Bs = 4) is selected (Yes in step S103). ). On the other hand, when the block boundary does not become a macroblock boundary, that is, when these two blocks are included in the same macroblock, the second strength (Bs = 3) is selected (No in step S103).

  As a result of the above determination (step S102), when both the block p and the block q are not intra-coded (No in step S102), one of these two blocks then selects the spatial frequency component after orthogonal transformation. It is determined whether or not the indicated coefficient is included (step S104). If either of the two blocks includes a coefficient (Yes in step S104), the third strongest filter strength (Bs = 2) is selected. On the other hand, when both of the two blocks do not include a coefficient, that is, when the coefficient is not encoded in both the block p and the block q (No in step S104), in order to select whether or not the filtering is skipped. Next determination is performed (step S105).

It is determined whether or not the index numbers Ref (p) and Ref (q) of the reference pictures in both the block p and the block q are the same. Also, the vertical (V (p, y) and V (q, y)) and horizontal (V (p, x) and V (q, x)) motion vectors of the two blocks are compared with each other, and more than one pixel. Determine if there is a small difference. As a result of the two determinations, only when the index numbers of the reference pictures of the two blocks are the same and their vertical and horizontal motion vectors are not separated from one pixel (No in step S105), these two Filtering the boundaries between blocks is skipped. In all other cases (Yes in step S105), weak filtering (Bs = 1) is performed at the block boundary.
Joint Video Team (JVT) of ISO / IEC MPEG and ITU-T VCEG Joint Committee Draft 2002-05-10, JVT-C167 9.5 Deblocking Filter

  Conventional decision algorithms for selecting filter strengths do not fully cover all possible cases for a block in a predictively coded picture that references two pictures. This is because a macroblock of a predictive coded picture that refers to two pictures can be predicted using direct, forward, backward, and modes that refer to two pictures. These prediction modes are not considered in the conventional determination algorithm. Similarly, when one block uses the direct mode and the other block uses a prediction mode that references two pictures, the motion vectors used for comparison are not fully described in the prior art.

  Therefore, the present invention has been made in view of the above circumstances, and a filtering strength determination method capable of determining an optimal filtering strength even when predictive coding that refers to two pictures is used, It is an object of the present invention to provide a moving image encoding method and a moving image decoding method.

  In order to achieve the above object, a filtering strength determination method according to the present invention is a filtering strength determination method that determines the strength of filtering for removing coding distortion between blocks constituting a picture, and is encoded. A parameter acquisition step of acquiring a parameter that is information at the time of encoding of the target block and the encoded adjacent block adjacent to the target block, and the picture including the target block and the adjacent block refers to two pictures In the case of a picture to be subjected to inter-picture predictive coding, it includes a comparison step for comparing the parameters of the target block and the adjacent block, and a determination step for determining the strength of filtering based on the comparison result of the comparison step. It is characterized by.

  Here, the parameter includes a coding mode of a block, and the comparison step refers to a reference that the target block and the neighboring block refer to based on the coding mode of the target block and the neighboring block, respectively. It may include a picture number determining step for determining whether or not the number of pictures is the same. In the determining step, different filtering strengths may be determined according to the determination result in the picture number determining step.

  The parameter further includes a reference index for uniquely identifying a reference picture, and the comparing step further includes the target block and the reference block based on the reference index of each of the target block and the neighboring block. A reference picture determination step for determining whether or not the reference pictures referenced by the adjacent blocks are the same, and in the determination step, different filtering strengths are determined according to a determination result in the reference picture determination step. May be.

  The parameter includes a motion vector with respect to a reference picture, and the comparison step further includes a horizontal component of an arbitrary motion vector of the target block based on the motion vector included in the target block and the adjacent block. And a difference between a horizontal component of an arbitrary motion vector of the adjacent block or a vertical component of an arbitrary motion vector of the target block and a vertical component of an arbitrary motion vector of the adjacent block, A motion vector determination step for determining whether or not the value is equal to or greater than a predetermined value may be included, and in the determination step, different filtering strengths may be determined according to a determination result in the motion vector determination step.

  This makes it possible to cover all possible cases for a block in a predictive coded picture that references two pictures, even if predictive coding that refers to two pictures is used. It is possible to optimally determine the filtering strength of a filter that filters image data and removes block distortion (encoding distortion between blocks) that is high-frequency noise near the boundary between blocks. Further, this filtering strength determination method can be applied to both the moving picture coding apparatus and the moving picture decoding apparatus.

  Also, the filtering strength determination method according to the present invention is a filtering strength determination method for determining the strength of filtering for removing coding distortion between blocks constituting a picture. A parameter acquisition step for acquiring a picture type of a picture including an encoded adjacent block adjacent to the block, and an inter-picture predictive encoding in which the picture type acquired by the parameter acquisition step refers to two pictures In some cases, the method includes a determination step of determining the strength of filtering more strongly than the case of indicating inter-picture predictive coding referring to one picture.

  As a result, even when predictive coding that refers to two pictures is used as described above, the decoded image data is filtered to generate block distortion (high-frequency noise near the boundary between blocks). The filtering strength of the filter that removes (distortion) can be optimally determined. Further, this filtering strength determination method can be applied to both the moving picture coding apparatus and the moving picture decoding apparatus.

  The moving picture coding method according to the present invention is a moving picture coding method for coding each picture constituting a moving picture in units of blocks, and the filtering determined by the filtering strength determination method according to the present invention. A filtering step of filtering between the target block and the adjacent block according to intensity is included.

  The moving picture decoding method according to the present invention is a moving picture decoding method for decoding moving picture encoded data in which each picture constituting a moving picture is encoded in units of blocks. A filtering step of performing filtering between the target block and the adjacent block according to the filtering strength determined by the filtering strength determining method is included.

  The present invention can be realized not only as such a filtering strength determination method, a moving image encoding method and a moving image decoding method, but also as such a filtering strength determination method, a moving image encoding method, and Realized as a filtering strength determination device, a moving image coding device, and a moving image decoding device having the characteristic steps included in the moving image decoding method as a means, or realized as a program for causing a computer to execute these steps You can also Needless to say, such a program can be distributed via a recording medium such as a CD-ROM or a transmission medium such as the Internet.

  As is clear from the above description, according to the filtering strength determination method according to the present invention, even when predictive coding that refers to two pictures is used, the decoded image data is filtered to block between blocks. It is possible to optimally determine the filtering strength of a filter that removes block distortion, which is high-frequency noise near the boundary. Therefore, the moving image can be encoded so as to improve the image quality of the decoded moving image. Further, the filtering strength determination method according to the present invention can be applied to both the moving picture coding apparatus and the moving picture decoding apparatus, and its practical value is great.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a moving picture coding apparatus using a filtering strength determination method according to the present invention.

  The moving image encoding device is a device that compresses and encodes an input moving image and outputs it as a code string. As shown in FIG. 1, a picture memory 101, a difference calculation unit 102, a prediction residual encoding unit 103, a code Sequence generation unit 104, prediction residual decoding unit 105, addition operation unit 106, motion vector detection unit 107, motion vector storage unit 108, motion compensation encoding unit 109, filter processing control unit 110, picture memory 111, switch 112, 113 and an inter-pixel filter 114 are provided.

  The picture memory 101 stores moving images input in units of pictures in order of display time. Here, a picture means one encoding unit called a screen including both a frame and a field. The motion vector detection unit 107 uses the encoded decoded image data as a reference picture, and detects a motion vector indicating a position predicted to be optimal in the search area in the picture. The motion vector detection unit 107 notifies the detected motion vector to the motion compensation encoding unit 109 and the motion vector storage unit 108.

  The motion compensation encoding unit 109 determines a block encoding mode using the motion vector detected by the motion vector detection unit 107, and generates predicted image data based on the encoding mode. This encoding mode indicates how the macroblock is encoded, and indicates whether it is non-intra encoding (motion compensation encoding) or intra encoding. For example, when the correlation between pictures is low and intra coding is preferable to performing motion prediction, intra coding is selected. This encoding mode is notified to the filter control unit 110. In addition, the motion vector and the encoding mode are notified from the motion compensation encoding unit 109 to the code string generation unit 104. The motion vector storage unit 108 stores the motion vector detected by the motion vector detection unit 107.

  The difference calculation unit 102 calculates a difference between the image data read from the picture memory 101 and the prediction image data input from the motion compensation encoding unit 109, and generates prediction residual image data. The prediction residual encoding unit 103 performs encoding processing such as orthogonal transformation and quantization on the input prediction residual image data to generate encoded data. The code string generation unit 104 performs variable-length encoding or the like on the encoded data generated by the prediction residual encoding unit 103, and further, information on the motion vector input from the motion compensation encoding unit 109, and encoding A code string is generated by adding mode information and the like.

  The prediction residual decoding unit 105 performs decoding processing such as inverse quantization and inverse orthogonal transform on the input encoded data, and generates decoded differential image data. The addition operation unit 106 adds the decoded differential image data input from the prediction residual decoding unit 105 and the predicted image data input from the motion compensation encoding unit 109 to generate decoded image data. The picture memory 111 stores the filtered decoded image data.

  The filter processing control unit 110 performs filtering strength of the inter-pixel filter 114, that is, the filter A 114a, the filter B 114b, the filter C 114c, the filter D 114d, and no filtering (skip) according to the input motion vector and encoding mode. Of which one to use is selected, and the switch 112 and the switch 113 are controlled. The switch 112 and the switch 113 are switches that selectively connect any one of the terminals “1” to “5” under the control of the filter processing control unit 110. The switch 113 is provided between the output terminal of the addition operation unit 106 and the input terminal of the inter-pixel filter 114. The switch 112 is provided between the input terminal of the picture memory 111 and the output terminal of the inter-pixel filter 114.

  The inter-pixel filter 114 is, for example, a deblocking filter that filters decoded image data and removes block distortion that is high-frequency noise in the vicinity of the boundary between the blocks. The filter A 114a, the filter B 114b, C114c and filter D114d are provided. The filter A 114a, the filter B 114b, the filter C 114c, and the filter D 114d have the strongest filtering strength, the filter B 114b, the filter C 114c, and the filter D 114d have the filtering strengths in order, and the filter D 114d has the weakest filtering strength. Also, the amount of calculation processing for filtering differs according to the filtering strength. The illustrated configuration such as the switch 112 and the switch 113 may be implemented as hardware or software.

  FIG. 2 is an explanatory diagram showing the order of pictures in the picture memory 101, and is an explanatory diagram showing (a) the input order and (b) the rearranged order. Here, the vertical line indicates a picture, and the symbol shown at the lower right of each picture is that the first alphabet is the picture type (I, P, or B), and the second and subsequent numbers are picture numbers in display time order. Is shown. A P picture uses a neighboring I picture or P picture in front in display time order as a reference picture, and a B picture has a neighboring I picture or P picture in front in display time order and rear in display time order. One neighboring I picture or P picture is used as a reference picture.

  FIG. 3 is an explanatory diagram of pictures and reference indexes. The reference index is used to uniquely identify a reference picture stored in the picture memory 111, and is a number associated with each picture as shown in FIG. The reference index is used to indicate a reference picture to be used when a block is encoded by inter picture prediction.

  As the value of the first reference index, first, in the information indicating the display order, a value starting from “0” is assigned to the reference picture before the encoding target picture from the order closest to the encoding target picture. When a value starting from “0” is assigned to all the reference pictures before the encoding target, the subsequent values are assigned to the reference pictures after the encoding target picture in order from the closest to the encoding target picture. .

  As the value of the second reference index, first, in the information indicating the display order, a value starting from “0” is assigned to the reference picture after the encoding target picture in the order closest to the encoding target picture. When values starting from “0” are assigned to all the reference pictures after the encoding target, subsequent values are assigned to the reference pictures before the encoding target picture in order from the closest to the encoding target picture. .

  For example, in FIG. 3, when the first reference index Ridx1 is “0” and the second reference index Ridx2 is “1”, the forward reference picture is a B picture with picture number 7 and the backward reference picture is picture number 9 P picture. Here, the picture number is a number indicating the display order. FIG. 3 shows an example of how to assign a reference index, and the way of assignment is not limited to the example of FIG.

  Next, the operation of the moving picture coding apparatus configured as described above will be described.

  For example, as shown in FIG. 2A, the input image is input to the picture memory 101 in picture units in order of display time. When the picture type to be encoded is determined, the pictures input to the picture memory 101 are rearranged in the order of encoding as shown in FIG. 2B, for example. This rearrangement to the coding order is performed based on the reference relationship in the inter-picture predictive coding, and the picture used as the reference picture is rearranged so that it is coded before the picture used as the reference picture. . Note that the picture type is generally determined by, for example, a method of periodically assigning picture types.

  Each picture that has been rearranged in the picture memory 101 is read in units of macroblocks divided into groups of horizontal 16 × vertical 16 pixels, for example. Also, motion compensation and motion vector extraction are performed in units of blocks divided into groups of, for example, horizontal 8 × vertical 8 pixels.

  The target macroblock read from the picture memory 101 is input to the motion vector detection unit 107 and the difference calculation unit 102.

  The motion vector detection unit 107 uses the decoded image data stored in the picture memory 111 as a reference picture, and detects a motion vector for each block in the macroblock. Then, the motion vector detection unit 107 outputs the detected motion vector and a reference index indicating the reference picture to the motion compensation encoding unit 109.

  The motion compensation encoding unit 109 uses the motion vector detected by the motion vector detection unit 107 and the reference index to determine a macroblock encoding mode. Here, for example, in the case of a B picture, the encoding mode is intra-picture encoding, inter-picture prediction encoding using a forward motion vector, inter-picture prediction encoding using a backward motion vector, and two motion vectors. It is assumed that it is possible to select which method to encode from among the inter-picture predictive encoding and the direct mode used.

  Here, the inter-picture prediction method in the direct mode will be described with reference to FIG. FIG. 4 is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B8 is encoded in the direct mode. In this case, a motion vector c having a block b at the same position as the block a in the picture P9 which is a reference picture behind the picture B8 is used. The motion vector c is a motion vector used when the block b is encoded, and refers to the picture P5. The block a uses the motion vector d for the picture P5 that is the forward reference picture obtained by scaling the motion vector c, and the motion vector e for the picture P9 that is the backward reference picture, and Motion compensation is performed.

  The motion compensation encoding unit 109 generates predicted image data based on the determined encoding mode, and outputs the predicted image data to the difference calculation unit 102 and the addition calculation unit 106. When the motion compensation encoding unit 109 selects the direct mode, the motion vector of the block at the same position as the target block in the backward reference picture is used as the reference motion vector as described above. The compensation encoding unit 109 reads the reference motion vector and the reference index from the motion vector storage unit 108. In addition, when the motion compensation encoding unit 109 selects intra-picture encoding, the predicted image data is not output. Also, the motion compensation encoding unit 109 performs filtering processing on the value of the reference index indicating the reference picture to the filtering processing control unit 110 and the code string generation unit 104 with respect to the determined encoding mode, motion vector, and reference index information. Output to the control unit 110.

  The difference calculation unit 102 to which the prediction image data is input from the motion compensation encoding unit 109 calculates a difference between the prediction image data and the image data of the macroblock of the picture B11 read from the picture memory 101, and performs prediction. Residual image data is generated and output to the prediction residual encoding unit 103.

  The prediction residual encoding unit 103 to which the prediction residual image data is input performs encoding processing such as orthogonal transformation and quantization on the prediction residual image data, generates encoded data, and generates a code string. Unit 104 and prediction residual decoding unit 105. The code string generation unit 104 to which the encoded data is input performs variable-length encoding or the like on the encoded data, and further, motion vector information and encoding mode information input from the motion compensation encoding unit 109. Etc., a code string is generated and output. For macroblocks encoded in the direct mode, motion vector information is not added to the encoded sequence.

  On the other hand, the prediction residual decoding unit 105 performs decoding processing such as inverse quantization and inverse orthogonal transform on the input encoded data, generates decoded difference image data, and adds the decoded difference image data to the addition operation unit 106. Output. The addition operation unit 106 adds the decoded differential image data and the predicted image data input from the motion compensation encoding unit 109 to generate decoded image data, and the inter-pixel filter 114 via the switch 113. Output to.

  The inter-pixel filter 114 to which the decoded image data is input filters or filters the decoded image data by any of the filter A 114a, the filter B 114b, the filter C 114c, and the filter D 114d selected by the switches 112 and 113. First, it is stored in the picture memory 111 via the switch 112. At this time, control for switching the terminals “1” to “5” of the switch 112 and the switch 113 is performed by the filter processing control unit 110 as follows.

  FIG. 5 is a flowchart illustrating a filtering strength determination method in the filter processing control unit 110.

  The filter processing control unit 110 determines the filtering strength necessary for both the vertical and horizontal block boundaries in the decoded image data. The determination for selecting the strength of the filter used for filtering is executed at the block boundary between two adjacent blocks p and q as in the conventional case shown in FIG. 13 (step S201). First, based on the encoding mode of each macroblock output from the motion compensation encoding unit 109, the filter processing control unit 110 determines whether or not these blocks p or q are intra-picture (intra) encoding. Is determined (step S202). Here, when one of the block p or the block q is intra-encoded (Yes in step S202), the filter processing control unit 110 determines whether or not the block boundary becomes a macroblock boundary ( Step S203).

  As a result of this determination, if the block boundary becomes a macroblock boundary, that is, if two blocks are not included in the same macroblock, the filter processing control unit 110 uses the filter A 114a (Bs = 4) having the strongest filtering strength. Is selected (Yes in step S203). That is, the filter processing control unit 110 performs control to switch each terminal of the switch 112 and the switch 113 to “1”. On the other hand, if the block boundary does not become a macroblock boundary, that is, if these two blocks are included in the same macroblock, the filter processing control unit 110 selects the second strength filter B114b (Bs ≧ 3). (No in step S203). That is, the filter processing control unit 110 performs control to switch each terminal of the switch 112 and the switch 113 to “2”. Here, Bs ≧ 3 indicates that Bs is at least a value of 3 or more under the conditions shown in this flowchart, and whether Bs = 3 or Bs is a value greater than 3 is not disclosed here. Determined by the conditions. Hereinafter, the formula including this inequality sign indicates a range that can be determined under conditions not disclosed in the present invention.

  As a result of the determination (step S202), when both the block p and the block q are not intra-coded (No in step S202), the filter processing control unit 110 determines whether either the block p or the block q is used. It is determined whether or not a coefficient indicating a spatial frequency component after orthogonal transformation is included (step S204). If either of the two blocks includes a coefficient (Yes in step S204), the filter processing control unit 110 selects the filter C114c (Bs ≧ 2) having the third strongest filtering strength. That is, the filter processing control unit 110 performs control to switch each terminal of the switch 112 and the switch 113 to “3”.

  On the other hand, when both of the two blocks do not include the coefficient, that is, when the coefficient is not encoded in both the block p and the block q (No in step S204), the filter processing control unit 110 changes the block p and the block q to each other. It is determined whether the included picture is a P picture or a B picture (step S205). Here, when the picture including the block p and the block q is a P picture, the filter processing control unit 110 is input from the reference index value and motion vector storage unit 108 input from the motion compensation encoding unit 109. Based on the motion vectors, the reference pictures referenced by the blocks p and q are the same, and the vertical components (V (p, y) and V (q, y)) of the motion vectors of the blocks p and q and It is determined whether or not the difference between the horizontal components (V (p, x) and V (q, x)) is smaller than one pixel (step S208). That is, whether all of the following formulas (A), (B), and (C) are satisfied.

  Here, Ref (p) and Ref (q) indicate reference pictures referenced by the block p and the block q, respectively.

  As a result of the determination, when the reference pictures referred to by the block p and the block q are the same and the difference between the vertical and horizontal motion vectors of the block p and the block q is less than one pixel (Yes in step S208), The filter processing control unit 110 selects no filtering (Bs = 0). That is, the filter processing control unit 110 performs control to switch each terminal of the switch 112 and the switch 113 to “5”. On the other hand, in other cases (No in step S208), the filter processing control unit 110 selects the filter D114d (Bs ≧ 1) having the weakest filtering strength. That is, the filter processing control unit 110 performs control to switch each terminal of the switch 112 and the switch 113 to “4”.

  As a result of the above determination (step S205), when the picture including the block p and the block q is a B picture, the coding mode of the macroblock is the inter-picture predictive coding using the forward motion vector, the backward motion vector. The inter-picture predictive coding used, the inter-picture predictive coding using two motion vectors, or the direct mode. For example, when block p uses only forward prediction and block q uses prediction that refers to two pictures, the number of reference pictures in block p is “1” and the number of reference pictures in block q Is “2”. Therefore, the filter processing control unit 110 determines whether or not the number of reference pictures referenced by the block p and the block q is the same (step S206). As a result, when the number of reference pictures to which the block p and the block q refer is different (No in step S206), the filter processing control unit 110 selects the filter D114d (Bs ≧ 1) having the weakest filtering strength.

  On the other hand, when the number of reference pictures referenced by the block p and the block q is the same (Yes in step S206), the filter processing control unit 110 is based on the reference index value input from the motion compensation encoding unit 109. Then, it is determined whether or not the reference pictures referred to by the block p and the block q are exactly the same (step S207). As a result, if even one reference picture is referenced by the block p and the block q (No in step S207), the filter processing control unit 110 selects the filter D114d (Bs ≧ 1) having the weakest filtering strength. .

  On the other hand, when the reference pictures referred to by the block p and the block q are exactly the same (Yes in step S207), the filter processing control unit 110 has the same weighted prediction weighting (ABP) coefficients in the block p and the block q. It is determined whether or not there is (step S209). As a result, when the weighting coefficients of the block p and the block q are different (No in step S209), the filter processing control unit 110 selects the filter D114d (Bs ≧ 1) having the weakest filtering strength. Here, the weighted prediction is a prediction method in which, in inter-picture prediction, a value obtained by multiplying a pixel value of a reference image by a first weighting factor α and further adding a second weighting factor β is a predicted pixel value. That is.

  On the other hand, when the weighting coefficients of the block p and the block q are the same (Yes in step S209), the filter processing control unit 110 determines that the difference between the vertical and horizontal motion vectors for all the motion vectors of the block p and the block q is It is determined whether the number is less than one pixel (step S210). That is, whether all of the following formulas (D) to (G) are satisfied.

  Here, Vf and Vb represent motion vectors in the blocks p and q, respectively. For example, when there is one reference picture, there is only one.

  If the result of this determination is that the difference between the vertical and horizontal motion vectors for all the motion vectors in block p and block q is less than one pixel (Yes in step S210), the filter processing control unit 110 performs filtering. None (Bs = 0) is selected. On the other hand, in other cases (No in step S210), the filter processing control unit 110 selects the filter D114d (Bs ≧ 1) having the weakest filtering strength.

  As described above, a macroblock of a B picture can be predicted using the direct mode. When the direct mode is used, the motion vector of the target block is derived from the motion vector of the block corresponding to the same position as the target block in the reference picture whose second reference index Ridx2 is “0”. In this case, the forward reference picture of the target block is a reference picture referred to by the motion vector of the corresponding block, and the backward reference picture of the target block is a reference picture whose second reference index Ridx2 is “0”. Therefore, the filter processing control unit 110 uses the derived motion vector and reference picture to determine the filtering strength.

  As described above, when the picture including the block p and the block q is a B picture, whether or not the number of reference pictures to which the block p and the block q refer is the same, and the reference picture to be referred to is exactly the same. Therefore, the optimum filtering strength can be determined even when predictive coding that refers to two pictures is used. Therefore, the moving image can be encoded so as to improve the image quality of the decoded moving image.

  FIG. 6 is a block diagram showing a configuration of a moving picture decoding apparatus using the filtering strength determination method according to the present invention.

  The video decoding device is a device that decodes the code sequence encoded by the video encoding device, and as shown in FIG. 6, a code sequence analysis unit 201, a prediction residual decoding unit 202, and motion compensation decoding. A unit 203, a motion vector storage unit 204, a filter processing control unit 205, a picture memory 206, an addition operation unit 207, switches 208 and 209, and an inter-pixel filter 210.

  The code string analysis unit 201 extracts various data such as information on the coding mode and information on the motion vector used at the time of coding from the input code string. The prediction residual decoding unit 202 decodes the input prediction residual encoded data, and generates prediction residual image data. The motion compensation decoding unit 203 obtains image data from the reference picture stored in the picture memory 206 based on the coding mode information and the motion vector information at the time of coding, and generates motion compensated image data. To do. The motion vector storage unit 204 stores the motion vector extracted by the code string analysis unit 201. The addition operation unit 207 adds the prediction residual image data input from the prediction residual decoding unit 202 and the motion compensated image data input from the motion compensation decoding unit 203 to generate decoded image data. . The picture memory 206 stores the filtered decoded image data.

  The filter processing control unit 205 selects the filtering strength of the inter-pixel filter 210, that is, which of the filter A 210a, the filter B 210b, the filter C 210c, the filter D 210d, and the non-filtering (skip) is used, and the switch 208 and The switch 209 is controlled. The switch 208 and the switch 209 are switches that selectively connect any of the terminals “1” to “5” under the control of the filter processing control unit 205. The switch 209 is provided between the output terminal of the addition operation unit 207 and the input terminal of the inter-pixel filter 210. The switch 208 is provided between the input terminal of the picture memory 206 and the output terminal of the inter-pixel filter 210.

  The inter-pixel filter 210 is, for example, a deblocking filter that filters the decoded image data and removes block distortion that is high-frequency noise in the vicinity of the boundary between the blocks. Each of the filters A210a, B210b, C210c and filter D210d are provided. The filter A 210a, the filter B 210b, the filter C 210c, and the filter D 210d have the strongest filtering strength, the filter B 210b, the filter C 210c, and the filter D 210d have the lowest filtering strength in this order, and the filter D 210d has the weakest filtering strength. Also, the amount of calculation processing for filtering differs according to the filtering strength.

  Next, the operation of the moving picture decoding apparatus configured as described above will be described.

  The code string analysis unit 201 extracts various data such as coding mode information and motion vector information from the input code string. The code string analysis unit 201 outputs the extracted encoding mode information to the motion compensation decoding unit 203 and the filter processing control unit 205, and outputs the motion vector information and the reference index to the motion vector storage unit 204. Further, the code string analysis unit 201 outputs the extracted prediction residual encoded data to the prediction residual decoding unit 202. The prediction residual decoding unit 202 to which the prediction residual encoded data is input decodes the prediction residual encoded data, generates prediction residual image data, and outputs the prediction residual image data to the addition calculation unit 207.

  On the other hand, the motion compensation decoding unit 203 is based on the coding mode information and the reference index value input from the code stream analysis unit 201 and the motion vector information read out from the motion vector storage unit 204, based on the picture memory 206. The motion compensation image data is generated with reference to the reference picture stored in. Next, the motion compensation decoding unit 203 outputs the generated motion compensated image data to the addition operation unit 207, and outputs a reference index value indicating a reference picture to the filter processing control unit 205. The addition operation unit 207 adds the motion compensated image data and the prediction residual image data input from the prediction residual decoding unit 202 to generate decoded image data, and the inter-pixel filter 210 via the switch 209. Output to.

  The inter-pixel filter 210 to which the decoded image data is input filters or filters the decoded image data by any of the filter A 210a, the filter B 210b, the filter C 210c, or the filter D 210d selected by the switches 208 and 209. Instead, it is stored in the picture memory 206 via the switch 208. At this time, control for switching the terminals “1” to “5” of the switch 208 and the switch 209 is performed by the filter processing control unit 205 in the same manner as the operation of the filter processing control unit 110 of the moving picture coding apparatus.

  As described above, when the picture including the block p and the block q is a B picture, whether or not the number of reference pictures to which the block p and the block q refer is the same, and the reference picture to be referred to is exactly the same. Therefore, the optimum filtering strength can be determined even when predictive coding that refers to two pictures is used. Therefore, it is possible to improve the image quality of moving images and perform decoding.

(Embodiment 2)
In the present embodiment, the filtering strength determination method in the filter processing control unit 110 described in the first embodiment is partially different. The configuration is the same as that of the first embodiment, and detailed description thereof is omitted. In addition, regarding the determination of the filtering strength in the filter processing control unit 110, the description of the same parts as those in the first embodiment will be omitted. In the case of a video decoding device, this is a method for determining the filtering strength in the filter processing control unit 205.

  FIG. 7 is a flowchart showing a filtering strength determination method according to the second embodiment.

  As a result of the determination (step S304) that either of the block p or the block q includes a coefficient indicating the spatial frequency component after the orthogonal transformation performed by the filter processing control unit 110, either of the two blocks is a coefficient. (Step S304: Yes), the following processing is performed.

  The filter processing control unit 110 determines whether a picture including the block p and the block q is a P picture or a B picture (step S311). When the picture including the block p and the block q is a P picture, the filter processing control unit 110 selects the filter C114c (Bs (p) ≧ 2) having the third strongest filtering strength. On the other hand, when the picture including the block p and the block q is a B picture, the filter processing control unit 110 uses Bs (b) (Bs (b )> Bs (p)).

  As described above, when either block p or block q includes a coefficient indicating a spatial frequency component after orthogonal transformation, it is determined whether a picture including block p and block q is a P picture or a B picture. Therefore, the optimum filtering strength can be determined even when predictive coding that refers to two pictures is used. Therefore, the moving image can be encoded so as to improve the image quality of the decoded moving image.

  In each of the above embodiments, when the filter processing control unit 110 selects not to perform filtering (Bs = 0), it does not perform filtering (skip), for example, the filter D114d (weakest filtering strength) A filter having a filtering strength lower than that of Bs ≧ 1) may be used.

  In each of the above embodiments, the filter processing control unit 110 does not have to execute all the steps shown in the flowchart of FIG. 5 or FIG. For example, if the result of determination in step S207 (S307) is that the reference pictures referenced by block p and block q are exactly the same (Yes in step S207 (S307)), the determination process in step S209 (S309) is performed. The determination process in step S210 (S310) may be performed without performing this process. Moreover, the execution order of each step may be changed.

  In each of the above embodiments, a picture is used as a coding unit. However, a field or a frame may be used.

(Embodiment 3)
Furthermore, by recording a program for realizing the configuration of the moving picture encoding method or the moving picture decoding method shown in each of the above embodiments on a storage medium such as a flexible disk, The processing shown in the form can be easily performed in an independent computer system.

  FIG. 8 is an explanatory diagram of a storage medium for storing a program for realizing the moving picture coding method and the moving picture decoding method of each embodiment by a computer system.

  FIG. 8B shows an appearance, a cross-sectional structure, and a flexible disk as seen from the front of the flexible disk, and FIG. 8A shows an example of a physical format of the flexible disk that is a recording medium body. The flexible disk FD is built in the case F, and a plurality of tracks Tr are formed concentrically on the surface of the disk from the outer periphery toward the inner periphery, and each track is divided into 16 sectors Se in the angular direction. ing. Therefore, in the flexible disk storing the program, a moving image encoding method as the program is recorded in an area allocated on the flexible disk FD.

  FIG. 8C shows a configuration for recording and reproducing the program on the flexible disk FD. When recording the program on the flexible disk FD, the moving picture encoding method or the moving picture decoding method as the program is written from the computer system Cs via the flexible disk drive FDD. Further, when the above moving image coding method is constructed in a computer system by a program in a flexible disk, the program is read from the flexible disk by a flexible disk drive and transferred to the computer system.

  In the above description, a flexible disk is used as the recording medium, but the same can be done using an optical disk. Further, the recording medium is not limited to this, and any recording medium such as an IC card or a ROM cassette capable of recording a program can be similarly implemented.

  Furthermore, application examples of the video encoding method and video decoding method shown in the above embodiment and a system using the same will be described.

  FIG. 9 is a block diagram showing an overall configuration of a content supply system ex100 that implements a content distribution service. The communication service providing area is divided into desired sizes, and base stations ex107 to ex110, which are fixed radio stations, are installed in each cell.

  The content supply system ex100 includes, for example, a computer ex111, a PDA (personal digital assistant) ex112, a camera ex113, a mobile phone ex114, a camera via the Internet ex101, the Internet service provider ex102, the telephone network ex104, and the base stations ex107 to ex110. Each device such as the attached mobile phone ex115 is connected.

  However, the content supply system ex100 is not limited to the combination as shown in FIG. 9, and any of the combinations may be connected. Further, each device may be directly connected to the telephone network ex104 without going through the base stations ex107 to ex110 which are fixed wireless stations.

  The camera ex113 is a device capable of shooting a moving image such as a digital video camera. The mobile phone is a PDC (Personal Digital Communications) system, a CDMA (Code Division Multiple Access) system, a W-CDMA (Wideband-Code Division Multiple Access) system, or a GSM (Global System for Mobile Communications) system mobile phone, Alternatively, PHS (Personal Handyphone System) or the like may be used.

  In addition, the streaming server ex103 is connected from the camera ex113 through the base station ex109 and the telephone network ex104, and live distribution or the like based on the encoded data transmitted by the user using the camera ex113 becomes possible. The encoded processing of the captured data may be performed by the camera ex113 or may be performed by a server or the like that performs data transmission processing. Further, the moving image data shot by the camera ex116 may be transmitted to the streaming server ex103 via the computer ex111. The camera ex116 is a device that can shoot still images and moving images, such as a digital camera. In this case, the encoding of the moving image data may be performed by the camera ex116 or the computer ex111. The encoding process is performed in the LSI ex117 included in the computer ex111 and the camera ex116. Note that moving image encoding / decoding software may be incorporated in any storage medium (CD-ROM, flexible disk, hard disk, or the like) that is a recording medium readable by the computer ex111 or the like. Furthermore, you may transmit moving image data with the mobile telephone ex115 with a camera. The moving image data at this time is data encoded by the LSI included in the mobile phone ex115.

  In this content supply system ex100, the content (for example, video shot of music live) captured by the user with the camera ex113, camera ex116, etc. is encoded and transmitted to the streaming server ex103 as in the above embodiment. On the other hand, the streaming server ex103 distributes the content data to the requested client. Examples of the client include a computer ex111, a PDA ex112, a camera ex113, a mobile phone ex114, and the like that can decode the encoded data. In this way, the content supply system ex100 can receive and reproduce the encoded data at the client, and also realize personal broadcasting by receiving, decoding, and reproducing in real time at the client. It is a system that becomes possible.

  For the encoding and decoding of each device constituting this system, the moving image encoding device or the moving image decoding device described in the above embodiments may be used.

  A mobile phone will be described as an example.

  FIG. 10 is a diagram showing the mobile phone ex115 using the moving picture coding method and the moving picture decoding method described in the above embodiment. The cellular phone ex115 includes an antenna ex201 for transmitting and receiving radio waves to and from the base station ex110, a camera such as a CCD camera, a camera unit ex203 capable of taking a still image, a video shot by the camera unit ex203, and an antenna ex201. A display unit ex202 such as a liquid crystal display that displays data obtained by decoding received video and the like, a main body unit composed of a group of operation keys ex204, an audio output unit ex208 such as a speaker for audio output, and audio input To store encoded data or decoded data such as a voice input unit ex205 such as a microphone, captured video or still image data, received mail data, video data or still image data, etc. Recording medium ex207, and slot portion ex20 for enabling recording medium ex207 to be attached to mobile phone ex115 The has. The recording medium ex207 stores a flash memory element, which is a kind of EEPROM (Electrically Erasable and Programmable Read Only Memory), which is a nonvolatile memory that can be electrically rewritten and erased, in a plastic case such as an SD card.

  Further, the cellular phone ex115 will be described with reference to FIG. The cellular phone ex115 controls the power supply circuit ex310, the operation input control unit ex304, and the image coding for the main control unit ex311 which is configured to control the respective units of the main body unit including the display unit ex202 and the operation key ex204. Unit ex312, camera interface unit ex303, LCD (Liquid Crystal Display) control unit ex302, image decoding unit ex309, demultiplexing unit ex308, recording / reproducing unit ex307, modulation / demodulation circuit unit ex306, and audio processing unit ex305 via a synchronization bus ex313 Are connected to each other.

  When the end call and power key are turned on by a user operation, the power supply circuit ex310 activates the camera-equipped digital mobile phone ex115 by supplying power from the battery pack to each unit. .

  The mobile phone ex115 converts the voice signal collected by the voice input unit ex205 in the voice call mode into digital voice data by the voice processing unit ex305 based on the control of the main control unit ex311 including a CPU, a ROM, a RAM, and the like. The modulation / demodulation circuit unit ex306 performs spread spectrum processing, and the transmission / reception circuit unit ex301 performs digital analog conversion processing and frequency conversion processing, and then transmits the result via the antenna ex201. In addition, the cellular phone ex115 amplifies the received data received by the antenna ex201 in the voice call mode, performs frequency conversion processing and analog-digital conversion processing, performs spectrum despreading processing by the modulation / demodulation circuit unit ex306, and analog audio by the voice processing unit ex305. After the data is converted, it is output via the audio output unit ex208.

  Further, when an e-mail is transmitted in the data communication mode, text data of the e-mail input by operating the operation key ex204 of the main body is sent to the main control unit ex311 via the operation input control unit ex304. The main control unit ex311 performs spread spectrum processing on the text data in the modulation / demodulation circuit unit ex306, performs digital analog conversion processing and frequency conversion processing in the transmission / reception circuit unit ex301, and then transmits the text data to the base station ex110 via the antenna ex201.

  When transmitting image data in the data communication mode, the image data captured by the camera unit ex203 is supplied to the image encoding unit ex312 via the camera interface unit ex303. When image data is not transmitted, the image data captured by the camera unit ex203 can be directly displayed on the display unit ex202 via the camera interface unit ex303 and the LCD control unit ex302.

  The image encoding unit ex312 is configured to include the moving image encoding device described in the present invention, and the image data supplied from the camera unit ex203 is a code used in the moving image encoding device described in the above embodiment. The encoded image data is converted into encoded image data by compression encoding using the encoding method, and is sent to the demultiplexing unit ex308. At the same time, the cellular phone ex115 sends the sound collected by the audio input unit ex205 during imaging by the camera unit ex203 to the demultiplexing unit ex308 as digital audio data via the audio processing unit ex305.

  The demultiplexing unit ex308 multiplexes the encoded image data supplied from the image encoding unit ex312 and the audio data supplied from the audio processing unit ex305 by a predetermined method, and the multiplexed data obtained as a result is a modulation / demodulation circuit unit A spectrum spread process is performed at ex306, a digital-analog conversion process and a frequency conversion process are performed at the transmission / reception circuit unit ex301, and then transmitted through the antenna ex201.

  When data of a moving image file linked to a homepage or the like is received in the data communication mode, the received data received from the base station ex110 via the antenna ex201 is subjected to spectrum despreading processing by the modulation / demodulation circuit unit ex306, and the resulting multiplexing is obtained. Is sent to the demultiplexing unit ex308.

  In addition, in order to decode multiplexed data received via the antenna ex201, the demultiplexing unit ex308 separates the multiplexed data into a bit stream of image data and a bit stream of audio data, and synchronizes them. The encoded image data is supplied to the image decoding unit ex309 via the bus ex313, and the audio data is supplied to the audio processing unit ex305.

  Next, the image decoding unit ex309 is configured to include the moving image decoding apparatus described in the present invention, and a bit stream of image data is decoded by a decoding method corresponding to the encoding method described in the above embodiment. Reproduction moving image data is generated by decoding, and this is supplied to the display unit ex202 via the LCD control unit ex302, thereby displaying, for example, moving image data included in the moving image file linked to the homepage. . At the same time, the audio processing unit ex305 converts the audio data into analog audio data, and then supplies the analog audio data to the audio output unit ex208. Thus, for example, the audio data included in the moving image file linked to the home page is reproduced. The

  It should be noted that the present invention is not limited to the above-described system, and recently, digital broadcasting using satellites and terrestrial waves has become a hot topic. As shown in FIG. Any of the video decoding devices can be incorporated. Specifically, in the broadcasting station ex409, a bit stream of video information is transmitted to a communication or broadcasting satellite ex410 via radio waves. Receiving this, the broadcasting satellite ex410 transmits a radio wave for broadcasting, and receives the radio wave with a home antenna ex406 having a satellite broadcasting receiving facility, such as a television (receiver) ex401 or a set top box (STB) ex407. The device decodes the bitstream and reproduces it. In addition, the moving picture decoding apparatus described in the above embodiment can also be implemented in the playback apparatus ex403 that reads and decodes a bitstream recorded on a storage medium ex402 such as a CD or DVD that is a recording medium. . In this case, the reproduced video signal is displayed on the monitor ex404. A configuration is also possible in which a moving picture decoding apparatus is mounted in a set-top box ex407 connected to a cable ex405 for cable television or an antenna ex406 for satellite / terrestrial broadcasting, and this is reproduced on a monitor ex408 on the television. At this time, the moving picture decoding apparatus may be incorporated in the television instead of the set top box. It is also possible to receive a signal from the satellite ex410 or the base station ex107 by the car ex412 having the antenna ex411 and reproduce a moving image on a display device such as the car navigation ex413 that the car ex412 has.

  Furthermore, the image signal can be encoded by the moving image encoding apparatus shown in the above embodiment and recorded on a recording medium. As a specific example, there is a recorder ex420 such as a DVD recorder that records an image signal on a DVD disk ex421 or a disk recorder that records on a hard disk. Further, it can be recorded on the SD card ex422. If the recorder ex420 includes the moving picture decoding apparatus shown in the above embodiment, the image signal recorded on the DVD disc ex421 or the SD card ex422 can be reproduced and displayed on the monitor ex408.

  For example, the configuration of the car navigation ex413 may be a configuration excluding the camera unit ex203, the camera interface unit ex303, and the image encoding unit ex312 in the configuration illustrated in FIG. 11, and the same applies to the computer ex111 and the television (receiver). ) Ex401 can also be considered.

  In addition to the transmission / reception type terminal having both the encoder and the decoder, the terminal such as the mobile phone ex114 has three implementation formats: a transmitting terminal having only an encoder and a receiving terminal having only a decoder. Can be considered.

  As described above, the moving picture encoding method or the moving picture decoding method described in the above embodiment can be used in any of the above-described devices and systems, and as a result, the above-described embodiment has been described. An effect can be obtained.

  In addition, the present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the scope of the present invention.

It is a block diagram which shows the structure of the moving image encoder which concerns on this invention. It is explanatory drawing which shows the order of the picture in a picture memory, (a) The input order, (b) It is explanatory drawing which shows the rearranged order. It is explanatory drawing of a picture and a reference index. It is explanatory drawing which shows the motion vector in direct mode. 6 is a flowchart illustrating a filtering strength determination method in the filter processing control unit according to Embodiment 1. FIG. It is a block diagram which shows the structure of the moving image decoding apparatus which concerns on this invention. FIG. 10 is a flowchart illustrating a filtering strength determination method in a filter processing control unit according to the second embodiment. It is explanatory drawing about the recording medium for storing the program for implement | achieving the moving image encoding method and moving image decoding method of each embodiment by a computer system, (a) Of flexible disk which is a recording medium main body An explanatory diagram showing an example of a physical format, (b) an external view from the front of the flexible disk, a sectional structure, and an explanatory diagram showing the flexible disk, and (c) a configuration for recording and reproducing the program on the flexible disk FD It is explanatory drawing which showed. It is a block diagram which shows the whole structure of a content supply system. It is the schematic which shows the example of a mobile telephone. It is a block diagram which shows the structure of a mobile telephone. It is a figure which shows the example of the system for digital broadcasting. It is a flowchart which shows the determination method of the conventional filtering strength.

Explanation of symbols

101, 111, 206 Picture memory 102 Difference calculation unit 103 Prediction residual encoding unit 104 Code sequence generation unit 105, 202 Prediction residual decoding unit 106, 207 Addition calculation unit 107 Motion vector detection unit 108, 204 Motion vector storage unit 109 Motion Compensation Encoding Unit 110, 205 Filter Processing Control Unit 112, 113, 208, 209 Switch 114, 210 Interpixel Filter 201 Code Sequence Analysis Unit 203 Motion Compensation Decoding Unit

Claims (1)

A filtering strength determination method for determining a filtering strength for removing coding distortion between blocks constituting a B picture subjected to inter-picture prediction coding ,
In the inter-picture predictive encoding of the B picture, one or two reference pictures are specified from a plurality of reference pictures located in front of or behind the target picture, and each block of the target picture is motion-compensated. In the identification of the reference picture, it is possible to identify the same picture,
When the target block included in the target picture and the adjacent block adjacent to the target block are both inter-picture predictively encoded, and neither the target block nor the adjacent block has transform coefficient data, A reference picture number determination step for determining whether or not the target block and the adjacent block each refer to the same number of pictures;
A filtering strength determination step of selecting a predetermined filtering strength from a plurality of filtering strengths including a strength not to be filtered,
In the filtering strength determination step, when it is determined in the reference picture number determination step that the number of pictures to be referred to is different, the highest strength among the plurality of filtering strengths excluding the strength for which the filtering is not performed. A filtering strength determination method characterized by selecting a weak filter.

Images