JP4767992B2 - Variable length encoding method and variable length decoding method - Google Patents

Description

  The present invention relates to a variable-length encoding method and a variable-length decoding method when compressing and expanding an image signal.

  Standardization work is currently underway. In the H.264 coding method, two methods, a context adaptive variable length coding (hereinafter referred to as CAVLC) method and a context adaptive binary arithmetic coding (hereinafter referred to as CABAC) method, are defined as variable length coding methods.

  In the CAVLC method, encoding efficiency is improved by adaptively switching the VLC table using information (context) of neighboring blocks. In the CABAC system, the coding efficiency is improved by switching the probability table according to the context.

  A method for encoding or decoding the number of significant coefficients in a block in the CAVLC scheme will be described. Here, the significant coefficient is a coefficient whose coefficient value is not 0. In FIG. 5, it is assumed that block C is a block to be subjected to variable length coding, and blocks A and B are blocks located on the left and above block C, respectively. Here, for example, H.M. In the H.264 system, each block is frequency-converted with the size of 4 horizontal pixels and 4 vertical pixels regardless of the magnitude of motion compensation, and the maximum number of significant coefficients is 16. In this case, if the blocks A and B are both in the screen and are in the same slice, two average values are obtained for the number of significant coefficients of the blocks A and B, and the VLC table used according to the average value is calculated. change. For example, when the average value is 0 or 1, VLC0 in FIG. 4 is used, when the average value is 2 or 3, VLC1 in FIG. 4 is used, and when the average value is 5 or more, VLC2 in FIG. 4 is used. .

  Next, a method for encoding or decoding a bit (CBP bit) indicating whether each block has a significant coefficient in the CABAC system will be described. In FIG. 5, it is assumed that block C is a block to be subjected to variable length coding, and blocks A and B are blocks located on the left and above block C, respectively. In this case, if the blocks A and B are both in the screen, are in the same slice, and are the same type of blocks as the block C (for example, A, B, and C are all luminance signal blocks), Which of the four combinations of whether or not B has a significant coefficient is determined. Then, the probability table used when arithmetically coding the CBP bits is selected from the four patterns according to the pattern.

  Next, a method for encoding or decoding a bit indicating whether or not each coefficient in a block is a significant coefficient in the CABAC system will be described. FIG. 6 shows the coefficients in the block rearranged in a predetermined scanning order. Here H. In the H.264 system, a method of scanning in a zigzag order from a low frequency component to a high frequency component is used. At this time, whether each coefficient is a significant coefficient is expressed by bits called SIG bit and LAST bit, and these bits are arithmetically encoded. Here, the SIG bit is 1 when the coefficient is significant, and is 0 when the coefficient value is 0. The LAST bit is assigned only to the significant coefficient, and is 1 when the significant coefficient is the last coefficient in the block, and 0 otherwise. Here, the probability table when arithmetically encoding the SIG bit and the LAST bit is different depending on the type of block (for example, intra-screen prediction luminance signal block, inter-picture prediction luminance signal block, intra-screen prediction color difference signal block, inter-picture prediction color difference signal). Are prepared for each coefficient position (position in scanning order) for each block type. Thus, for example, if a block type has a maximum of 16 coefficients, 15 probability tables are used for each SIG bit and LAST bit. This is because if the 16th significant coefficient exists, the final coefficient does not need to be encoded.

  In the CABAC method, as a context that causes the probability table to be selected, in addition to the above-described CBP, SIG bit, and LAST bit, for example, an intra macroblock, a skip macroblock, a direct mode macroblock, or the like , Whether the reference picture number is 0, and whether the difference QP is 0. Then, with respect to these contexts, the context value of the target block is determined using the values of the blocks located to the left and above the block that is the target of arithmetic coding, and the variable length code using the probability table corresponding to the value Is going on. The bit string subjected to variable length coding is described in the code string as shown in FIG. In FIG. 24, a probability table is shown below each information. For example, when MB_type, which is a macroblock encoding mode, is variable length encoded, four probability tables (MB0 to MB3) are used according to the context value.

  However, in the conventional CAVLC method and CABAC method, selection of the VLC table and the probability table is based on the assumption that the frequency conversion blocks (hereinafter simply referred to as conversion blocks) have the same size. Since the methods are determined, there is a problem that these methods cannot be used when the size of the transform block is not constant.

  In addition, the conventional CAVLC method and CABAC method have a problem that they do not support the case where the image signal is an interlaced signal. In other words, since the interlaced signal is encoded / decoded in a frame or field structure for each block, the block to be encoded / decoded is different from the block located on the left or above. In some cases, coding / decoding is performed with a structure, but the conventional CAVLC scheme and CABAC scheme do not define a variable length coding decision method in the case of such an interlaced signal.

  Therefore, the present invention solves the above-described problem. When the size of the transform block is not constant, the VLC table improves the coding efficiency when the CAVLC method or the CABAC method is used as the variable length coding method. Another object of the present invention is to provide a variable-length encoding method and a variable-length decoding method that realize a method for selecting a probability table.

  In addition, the present invention realizes a method for selecting a VLC table or a probability table that improves coding efficiency when the CAVLC method or the CABAC method is used as the variable length coding method when the image signal is an interlace signal. It is another object of the present invention to provide a variable length encoding method and a variable length decoding method.

  In order to achieve the above object, a variable length coding method of the present invention is a variable length coding method used when an image is divided into a plurality of blocks and coding is performed in units of the blocks. When the variable length coding table used when coding the information of the target block is determined according to the information of the neighboring blocks of the coding target block, and the sizes of the coding target block and the neighboring blocks are different Is characterized in that the information on the peripheral blocks is used after being converted into the size of the block to be encoded.

  The variable length coding method according to the present invention is characterized in that the information is the number of significant coefficients of the block.

  The present invention can be realized not only as the variable length coding method and variable length decoding method described above but also as a variable length coding apparatus and variable length decoding provided with characteristic procedures included in the methods. It can also be realized as a device or as a program for causing a computer to execute these procedures. 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 described above, the variable length coding method and the variable length decoding method of the present invention encode the number of significant coefficients of each block by the CAVLC method, and the size of the encoding target block and the size of the surrounding blocks. Are different from each other, the number of significant coefficients of the surrounding blocks is converted based on the ratio of the size of the encoding target block to the surrounding blocks, and the converted value is used to determine the variable length coding table. .

  With the operation as described above, even when the size of the encoding target block is different from the size of the surrounding blocks, the variable length table can be determined according to the size of the encoding target block. It is possible to improve the conversion efficiency.

  Also, the variable length coding method of the present invention uses the CABAC method to encode a bit (CBP bit) indicating whether each block has a significant coefficient or not. If the size is different, the presence / absence of a significant coefficient in the surrounding block is converted based on the ratio of the size of the encoding target block to the surrounding block, and the probability table used in the CABAC method is determined. Used for.

  With the operation as described above, even when the size of the encoding target block and the size of the surrounding blocks are different, the probability table can be determined according to the size of the encoding target block, Efficiency can be improved.

  The variable length coding method of the present invention uses a CABAC method to encode a bit indicating whether or not each coefficient in a block is a significant coefficient. Prepare a different set of probability tables for each block size. Alternatively, a probability table is prepared in accordance with the maximum block size of the encoding target block, and the same set of probability tables is used regardless of the difference in block size.

  By the operation as described above, even if a block has a plurality of sizes, it is possible to improve the coding efficiency by having a set of probability tables for each block size. In addition, by preparing a probability table according to the maximum block size and using the same set of probability tables regardless of the difference in block size, the number of probability tables can be reduced, and the memory size can be reduced. Can be small.

  Also, according to the present invention, when the image signal is interlaced, whether the target block and the peripheral block are encoded in the frame structure when the CAVLC method or the CABAC method is used as the variable length encoding / decoding method. The variable length coding table and the probability table are determined based on the coincidence and difference between the coding structures that are encoded in the field structure. Thus, even when a frame structure and a field structure block coexist, the VLC table and the probability table are uniquely determined, and the coding efficiency is improved.

  Embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
First, the overall operation of the video encoding apparatus will be described with reference to FIG. 1 shows a frame memory 101, a difference calculation unit 102, a prediction error encoding unit 103, a code string generation unit 104, a prediction error decoding unit 105, an addition calculation unit 106, a frame memory 107, a motion vector detection unit 108, and a mode selection. 1 is a block diagram of a video encoding apparatus including a unit 109, an encoding control unit 110, and switches 111 to 115. FIG.

  Assume that each picture rearranged in the frame memory 101 is read in units of macroblocks. Here, it is assumed that the macroblock has a size of horizontal 16 × vertical 16 pixels. Motion compensation is performed in units of 16 × 16, 16 × 8, 8 × 16, 8 × 8, 8 × 4, 4 × 8, and 4 × 4 blocks. Here, for example, 16 × 8 indicates a block having a size of 16 horizontal pixels and 8 vertical pixels. Here, the encoding of a forward reference predictive encoded picture (P picture) will be described as an example.

  In encoding a P picture, the encoding control unit 110 turns on the switch 113. When the P picture is used as a reference picture for other pictures, each switch is controlled so that the switches 114 and 115 are turned on. When not used as a reference picture for other pictures, the switches 114 and 115 are controlled to be turned off. Therefore, the macroblock of the P picture read from the frame memory 101 is first input to the motion vector detection unit 108, the mode selection unit 109, and the difference calculation unit 102.

  The motion vector detection unit 108 detects the forward motion vector of each block included in the macroblock by using the decoded picture data of the reference picture stored in the frame memory 107 as the forward reference picture.

  The mode selection unit 109 determines the macroblock coding mode using the motion vector detected by the motion vector detection unit 108. Here, it is assumed that the coding mode of the P picture can be selected from, for example, intra-picture coding and inter-picture prediction coding by forward reference. In addition, when inter-picture predictive coding based on forward reference is used, the coding mode also includes information on what block a macroblock is divided to perform motion compensation.

  The encoding mode determined by the mode selection unit 109 is output to the code string generation unit 104. Further, a reference image based on the encoding mode determined by the mode selection unit 109 is output to the difference calculation unit 102 and the addition calculation unit 106. However, when intra-picture encoding is selected, the reference image is not output. Further, when intra-picture coding is selected by the mode selection unit 109, the switch 111 is controlled to be connected to a and the switch 112 is connected to c. When inter-picture predictive coding is selected, The switch 111 is controlled to be connected to b, and the switch 112 is connected to d. Hereinafter, a case where inter-picture prediction coding is selected by the mode selection unit 109 will be described.

  A reference image is input from the mode selection unit 109 to the difference calculation unit 102. The difference calculation unit 102 calculates the difference between the macroblock of the P picture and the reference image, and generates and outputs a prediction error image.

  The prediction error image is input to the prediction error encoding unit 103. The prediction error encoding unit 103 generates and outputs encoded data by performing encoding processing such as frequency conversion and quantization on the input prediction error image. Here, it is assumed that the frequency conversion for the prediction error image is performed based on the magnitude of motion compensation determined by the mode selection unit 109. For example, when motion compensation is performed with a size of 8 × 8 or more, frequency conversion is performed with a size of 8 × 8, and when motion compensation is performed with a size of less than 8 × 8, the same size as motion compensation is used. The frequency is converted by The encoded data output from the prediction error encoding unit 103 is input to the code string generation unit 104.

  The code string generation unit 104 performs variable length coding or the like on the input encoded data, and adds the information such as the encoding mode and header information input from the mode selection unit 109 to generate the code string. Is generated and output.

  Next, the overall operation of the moving picture decoding apparatus will be described with reference to FIG. FIG. 3 shows a code string analysis unit 301, a prediction error decoding unit 302, a mode decoding unit 303, a motion compensation decoding unit 305, a motion vector storage unit 306, a frame memory 307, an addition operation unit 308, switches 309 and 310, variable length FIG. 10 is a block diagram of a video decoding device configured by a decoding unit 311.

  Hereinafter, the decoding process of the forward prediction reference coded picture (P picture) will be described.

  The code string is input to the code string analysis unit 301. The code string analysis unit 301 extracts various data from the input code string. Here, the various data are mode selection information, motion vector information, and the like. The extracted mode selection information is output to mode decoding section 303. The extracted motion vector information is output to the motion compensation decoding unit 305. Further, the prediction error encoded data is output to the variable length decoding unit 311.

  The mode decoding unit 303 controls the switches 309 and 710 with reference to the mode selection information extracted from the code string. When the mode selection is intra-picture coding, the switch 309 is controlled to be connected to a, and the switch 710 is controlled to be connected to c. When the mode selection is inter picture predictive coding, control is performed so that the switch 309 is connected to b and the switch 710 is connected to d.

  The mode decoding unit 303 also outputs mode selection information to the motion compensation unit. Hereinafter, a case where the mode selection is inter-picture predictive coding will be described.

  The variable length decoding unit 311 performs variable length decoding on the input prediction error encoded data. The data subjected to the variable length decoding is output to the prediction error decoding unit 302.

  The prediction error decoding unit 302 generates a prediction error image by performing inverse quantization processing or inverse frequency transform on the input data. Here, it is assumed that the inverse frequency conversion is performed based on the magnitude of motion compensation determined by the mode selection unit 109. For example, when motion compensation is performed with a size of 8 × 8 or more, frequency conversion is performed with a size of 8 × 8, and when motion compensation is performed with a size of less than 8 × 8, the same size as motion compensation is used. The frequency is converted by The generated prediction error image is output to the switch 309. Here, since the switch 309 is connected to b, the prediction error image is output to the addition operation unit 308.

  The motion compensation decoding unit 305 performs a decoding process on the encoded motion vector input from the variable length decoding unit 311. Then, a motion compensated image is acquired from the frame memory 307 based on the decoded motion vector. The motion compensated image generated in this way is output to the addition operation unit 308.

  The addition operation unit 308 adds the input prediction error image and the motion compensated image to generate a decoded image. The generated decoded image is output to the frame memory 307 via the switch 310.

  Now, details of the operations of the code string generation unit 104 in the video encoding device described above and the variable length decoding unit 311 in the video decoding device will be described below.

  First, a method for encoding or decoding the number of significant coefficients of each block by the CAVLC method in the code string generation unit 104 or the variable length decoding unit 311 will be described.

  When encoding or decoding the number of significant coefficients of each block, the number of significant coefficients of the neighboring blocks is referred to. Here, a case will be described in which blocks located above and to the left of the target block are used as peripheral blocks. Assuming that all the peripheral blocks are in the screen and are in the same slice, when encoding or decoding the number of significant coefficients of the target block, variable length encoding is performed using the number of significant coefficients of the peripheral blocks. Determine the (decryption) table. Here, if the maximum number of significant coefficients of the target block is different from the maximum number of significant coefficients of the surrounding blocks, the number of significant coefficients of the surrounding blocks is set so that the maximum number of significant coefficients of the target block and the surrounding blocks match. Ask. Here, when the maximum value of the number of significant coefficients of the target block is N (for example, when the size of the target block is 8 × 8, N is 64), the significant coefficient obtained by referring to the surrounding blocks If the number is less than N / 8, a variable length code such as VLC0 in FIG. 4, VLC1 in FIG. 4 if N / 8 or more and less than N / 4, and VLC2 in FIG. 4 is used if N / 4 or more is used. The encryption (decryption) table is determined. Here, in FIG. 4, the variable length coding (decoding) table is shown only up to the case where the number of significant coefficients is 16. However, when these tables are used, the number of significant coefficients is expanded to 17 or more. To do. In the following, description will be made with reference to FIG. 2. In FIG. 2, it is assumed that block C is a block to be subjected to variable length coding or variable length decoding.

  A first example will be described with reference to FIG. In FIG. 2A, the blocks A1, A2, B1, and B2 are peripheral blocks located on the left and above the block C. Here, the block C has a size of 8 × 8, and the peripheral block has a size of 8 × 4. In this case, the sum of the number of significant coefficients of the blocks A1 and A2 is used as the number of significant coefficients of the block located on the left of the block C, and the number of significant coefficients of the block located on the block C is represented by the block B1. And the sum of the number of significant coefficients of B2. Then, the average value of the number of significant coefficients of the blocks located on the left and the top of the block C, that is, here, the sum of the number of significant coefficients of the blocks A1 and A2, and the sum of the number of significant coefficients of the blocks B1 and B2 The variable length encoding (decoding) table for encoding (decoding) the number of significant coefficients of the block C is determined based on the average value. Here, instead of using the sum of the number of significant coefficients of the blocks B1 and B2, the number of significant coefficients of the block B1 adjacent to the block C may be doubled.

  A second example will be described with reference to FIG. In FIG. 2B, blocks A1, A2, A3, A4, B1, B2, B3, and B4 are peripheral blocks located on the left and top of block C. Here, the block C has a size of 8 × 8, and the blocks A1, A2, A3, A4, B1, B2, B3, and B4 have a size of 4 × 4. In this case, as the number of significant coefficients of the block located on the left of the block C, the sum of the number of significant coefficients of the blocks A1, A2, A3, and A4 is used, and the number of significant coefficients of the block located on the block C is obtained. , The sum of the number of significant coefficients of the blocks B1, B2, B3, B4 is used. Then, the average value of the number of significant coefficients of the blocks located on the left and top of the block C, that is, here, the sum of the number of significant coefficients of the blocks A1, A2, A3, and A4 and the blocks B1, B2, B3, and B4 An average value with the sum of the number of significant coefficients is determined, and a variable-length encoding (decoding) table for encoding (decoding) the number of significant coefficients of the block C is determined based on the average value. Here, instead of using the sum of the number of significant coefficients of A1, A2, A3, A4, a value that is twice the sum of the number of significant coefficients of the blocks A2, A4 adjacent to the block C, or the blocks B1, B2, Instead of using the sum of the number of significant coefficients of B3 and B4, a value twice the sum of the number of significant coefficients of the blocks B3 and B4 adjacent to the block C may be used.

  A third example will be described with reference to FIG. In FIG. 2C, blocks A and B are peripheral blocks located on the left and top of block C. Here, the block C has a size of 8 × 4, and the blocks A and B have a size of 8 × 8. In this case, as the number of significant coefficients of the block located on the left of the block C, a value that is ½ of the number of significant coefficients of the block A is used, and as the number of significant coefficients of the block located on the block C, the block A value that is 1/2 of the number of significant coefficients of B is used. Then, the average value of the number of significant coefficients of the blocks located on the left and the upper side of the block C, that is, here, the value of 1/2 of the number of significant coefficients of the block A and 1 / number of the number of significant coefficients of the block B. An average value with the value of 2 is obtained, and a variable-length encoding (decoding) table for encoding (decoding) the number of significant coefficients of the block C is determined based on the average value.

  A fourth example will be described with reference to FIG. In FIG. 2D, blocks A1, A2, B1, and B2 are peripheral blocks positioned on the left and top of block C. Here, the block C has a size of 8 × 4, and the blocks A1, A2, B1, and B2 have a size of 4 × 8. In this case, as the number of significant coefficients of the block located on the left of the block C, a value that is ½ of the sum of the number of significant coefficients of the blocks A1 and A2 is used. As the number, a value half the sum of the number of significant coefficients of the blocks B1 and B2 is used. Then, the average value of the number of significant coefficients of the blocks located on the left and the top of the block C, that is, here, the value of ½ of the sum of the number of significant coefficients of the blocks A1 and A2, and the significance of the blocks B1 and B2 A variable length coding (decoding) table is obtained when an average value of the sum of the number of coefficients and a half value is obtained and the number of significant coefficients of the block C is encoded (decoded) by the average value. decide. Here, instead of using the sum of the number of significant coefficients of A1 and A2, instead of using the number of significant coefficients of one of the blocks A1 and A2 or the sum of the number of significant coefficients of the blocks B1 and B2, the block B1 , B2 may be used as the number of significant coefficients.

  A fifth example will be described with reference to FIG. In FIG. 2E, blocks A1, A2, A3, A4, B1, B2, B3, and B4 are peripheral blocks located on the left and top of block C. Here, the block C has a size of 8 × 4, and the blocks A1, A2, A3, A4, B1, B2, B3, and B4 have a size of 4 × 4. In this case, the sum of the number of significant coefficients of the blocks A1 and A2 is used as the number of significant coefficients of the block located on the left side of the block C, and the number of significant coefficients of the block located on the block C is represented by the block B3, The sum of the number of significant coefficients of B4 is used. Then, the average value of the number of significant coefficients of the blocks located on the left and top of the block C, that is, here, the sum of the number of significant coefficients of the blocks A1 and A2, and the sum of the number of significant coefficients of the blocks B3 and B4, The variable length encoding (decoding) table for encoding (decoding) the number of significant coefficients of the block C is determined based on the average value. Here, instead of using the sum of the number of significant coefficients of A1 and A2, the value of 1/2 of the number of significant coefficients of the blocks A1, A2, A3 and A4 and the number of significant coefficients of the blocks B3 and B4 are used. Instead of using the sum of the values, a value that is half the sum of the number of significant coefficients of the blocks B1, B2, B3, and B4 may be used.

  A sixth example will be described with reference to FIG. In FIG. 2F, blocks A and B are peripheral blocks located on the left and top of block C. Here, it is assumed that the block C has a size of 4 × 4, and the blocks A and B have a size of 8 × 8. In this case, the value of 1/4 of the number of significant coefficients of the block A is used as the number of significant coefficients of the block located on the left of the block C, and the number of significant coefficients of the block located on the block C is A value that is 1/4 of the number of significant coefficients of B is used. Then, the average value of the number of significant coefficients of the blocks located on the left and top of the block C, that is, here, the value of 1/4 of the number of significant coefficients of the block A and 1 / number of the number of significant coefficients of the block B An average value with the value of 4 is obtained, and a variable-length encoding (decoding) table for encoding (decoding) the number of significant coefficients of the block C is determined based on the average value.

  A seventh example will be described with reference to FIG. In FIG. 2G, blocks A1, A2, B1, and B2 are peripheral blocks located on the left and top of block C. Here, the block C has a size of 4 × 4, and has a size of the blocks A1, A2, B1, B2, 4 × 8. In this case, as the number of significant coefficients of the block located on the left of the block C, a value that is ½ of the number of significant coefficients of the block A2 is used, and as the number of significant coefficients of the block located above the block C, the block A value that is 1/2 of the number of significant coefficients of B1 is used. Then, the average value of the number of significant coefficients of the blocks located on the left and the top of the block C, that is, here, the value of 1/2 of the number of significant coefficients of the block A2, and 1 / number of the number of significant coefficients of the block B1. An average value with the value of 2 is obtained, and a variable-length encoding (decoding) table for encoding (decoding) the number of significant coefficients of the block C is determined based on the average value. Here, instead of using a value that is 1/2 of the number of significant coefficients of A2, a value that is 1/4 of the sum of the number of significant coefficients of blocks A1 and A2 or 1/2 of the number of significant coefficients of block B1 is used. Instead of using the value of, a value of ¼ of the sum of the number of significant coefficients of the blocks B1 and B2 may be used.

  Next, a method of encoding or decoding a bit (CBP bit) indicating whether each block has a significant coefficient by the CABAC method in the code string generation unit 104 or the variable length decoding unit 311 will be described.

  When the CBP bit of each block is encoded or decoded, the CBP bit of the peripheral block is referred to. Here, a case will be described in which blocks located above and to the left of the target block are used as peripheral blocks. Assuming that all the peripheral blocks are in the screen, are in the same slice, and are of the same type as the target block to be encoded (decoded), when the CBP bit of the target block is encoded or decoded, the peripheral block The probability table for variable length coding (decoding) is determined depending on the presence or absence of the significant coefficient. In this case, whether or not the total value of the number of significant coefficients of the block located to the left of the target block is 0, and the total value of the number of significant coefficients of the block located above the target block is 0. The probability table used when arithmetically coding the CBP bit of the target block is selected from the four combinations. Here, when the maximum number of significant coefficients of the target block is different from the maximum number of significant coefficients of the peripheral block, the CBP bit is obtained so that the maximum number of significant coefficients of the target block and the peripheral block are matched. In the following, description will be made with reference to FIG. 2. In FIG. 2, it is assumed that block C is a block to be subjected to variable length coding or variable length decoding.

  A first example will be described with reference to FIG. In FIG. 2A, blocks A1, A2, B1, and B2 are peripheral blocks located on the left and top of block C, respectively. In this case, there are four ways of determining whether the total number of significant coefficients of the blocks A1 and A2 is 0 and whether the total value of the number of significant coefficients of the blocks B1 and B2 is 0. Which combination is determined, thereby selecting a probability table to be used when arithmetically coding the CBP bits of block C. In this case, whether or not the number of significant coefficients in block A1 (or block A2) is 0 is used instead of using the criterion of whether or not the sum of the number of significant coefficients in blocks A1 and A2 is 0. And the number of significant coefficients in block B1 (or block B2) is 0 instead of using the criterion for determining whether or not the sum of the number of significant coefficients in blocks B1 and B2 is 0. It may be possible to use a criterion of whether or not.

  A second example will be described with reference to FIG. In FIG. 2 (b), blocks A1, A2, A3, A4, B1, B2, B3, and B4 are peripheral blocks located on the left and top of block C, respectively. In this case, whether the total value of the number of significant coefficients of the blocks A1, A2, A3, A3 is 0, and whether the total value of the number of significant coefficients of the blocks B1, B2, B3, B4 is 0 The probability table to be used when arithmetically coding the CBP bit of block C is selected. In this case, instead of using the criterion of whether or not the sum of the number of significant coefficients of the blocks A1, A2, A3, and A4 is 0, the number of significant coefficients of the blocks A2 and A4 adjacent to the block C Instead of using a criterion for determining whether the sum is 0 or a criterion for determining whether the sum of the number of significant coefficients of the blocks B1, B2, B3, and B4 is 0, a block adjacent to the block C A criterion of whether or not the sum of the number of significant coefficients of B3 and B4 is 0 may be used.

  A third example will be described with reference to FIG. In FIG. 2C, blocks A and B are peripheral blocks located on the left and above block C, respectively. In this case, it is determined whether there are four combinations of whether the number of significant coefficients in block A is 0 and whether the number of significant coefficients in block B is 0, and thereby A probability table used when arithmetically coding the CBP bits of block C is selected. In this case, instead of using the criterion of whether or not the number of significant coefficients in block A (block B) is 0, 1/2 of the number of significant coefficients in block A (block B) is 0. Or a criterion for determining whether the number of significant coefficients of block A (block B) is greater than or less than a predetermined value may be used.

  A fourth example will be described with reference to FIG. In FIG. 2D, blocks A1, A2, B1, and B2 are peripheral blocks located on the left and top of block C, respectively. In this case, there are four combinations of whether the sum of the number of significant coefficients of the blocks A1 and A2 is 0 and whether the sum of the number of significant coefficients of the blocks B1 and B2 is 0. Which is then selected, thereby selecting a probability table to be used when arithmetically coding the CBP bits of block C. Also, in this case, instead of using the criterion of whether or not the sum of the number of significant coefficients of the blocks A1 and A2 (blocks B1 and B2) is 0, the significant coefficient of the blocks A1 and A2 (blocks B1 and B2) A criterion for determining whether or not half of the sum of the numbers is 0, and a criterion for determining whether the number of significant coefficients of blocks A1 and A2 (blocks B1 and B2) is greater than or less than a predetermined value. It may be used.

  A fifth example will be described with reference to FIG. In FIG. 2 (e), blocks A1, A2, A3, A4, B1, B2, B3, and B4 are peripheral blocks located on the left and top of block C, respectively. In this case, there are four combinations of whether the sum of the number of significant coefficients of the blocks A1 and A2 is 0 and whether the sum of the number of significant coefficients of the blocks B3 and B4 is 0. Which is then selected, thereby selecting a probability table to be used when arithmetically coding the CBP bits of block C. In this case, instead of using the criterion of whether or not the sum of the number of significant coefficients of the blocks A1 and A2 is 0, the sum of the number of significant coefficients of the blocks A1, A2, A3, and A4, or the sum thereof Of whether or not 1/2 of the block B3 is equal to or greater than or less than a predetermined value and whether the sum of the number of significant coefficients of the blocks B3 and B4 is equal to 0 Instead of using the criterion, whether the sum of the number of significant coefficients of the blocks B1, B2, B3, B4, or ½ of the sum (rounded down value) is 0, or less than or equal to a predetermined value. A judgment criterion such as whether or not there is a possibility may be used.

  A sixth example will be described with reference to FIG. In FIG. 2F, blocks A and B are peripheral blocks located on the left and above block C, respectively. In this case, it is determined whether there are four combinations of whether the number of significant coefficients in block A is 0 and whether the number of significant coefficients in block B is 0, and thereby A probability table used when arithmetically coding the CBP bits of block C is selected. In this case, instead of using the criterion of whether or not the number of significant coefficients in block A (block B) is 0, 1/4 of the number of significant coefficients in block A (block B) is 0. A criterion for determining whether or not the number of significant coefficients of block A (block B) is greater than or less than a predetermined value may be used.

  A seventh example will be described with reference to FIG. In FIG. 2G, blocks A1, A2, B1, and B2 are peripheral blocks located on the left and top of block C, respectively. In this case, it is determined which of the four combinations of whether the number of significant coefficients of the block A2 is 0 and whether the number of significant coefficients of the block B1 is 0, and thereby, A probability table used when arithmetically coding the CBP bits of block C is selected. In this case, instead of using the criterion of whether or not the number of significant coefficients in block A2 (block B1) is 0, 1/2 of the number of significant coefficients in block A2 (block B1) is 0. Whether the number of significant coefficients in block A2 (block B1) is greater than or less than a predetermined value, and the sum of the number of significant coefficients in blocks A1 and A2 (blocks B1 and B2) Alternatively, a criterion such as whether or not half (the cut-off value) of the sum is 0, or whether it is greater than or less than a predetermined value may be used.

  Next, a coding method of bits indicating whether or not each coefficient in a block is a significant coefficient in the code string generation unit 104 or the variable length decoding unit 311 by the CABAC method will be described. As described with reference to FIG. 6 in the description of the conventional example, the coefficients in the block are rearranged in a predetermined scanning order and then expressed using SIG bits and LAST bits, and these bits are arithmetically encoded. Then.

  In the first example, a probability table for arithmetic coding of SIG bits and LAST bits is prepared for each block size. That is, a probability table is prepared such as a probability table for 4 × 4 blocks, a probability table for 4 × 8 blocks, a probability table for 8 × 4 blocks, and a probability table for 8 × 8 blocks. A probability table is prepared for each coefficient position (position in scanning order) for each block type. Thus, for example, for a 4 × 4 block, 15 probability tables are used for each of the SIG and LAST bits, and for an 8 × 8 block, for each of the SIG and LAST bits. 63 probability tables are used. This is because if there is a significant coefficient at the final position, this coefficient does not need to be encoded.

  In the second example, the probability table when the SIG bit and the LAST bit are arithmetically encoded is a set of tables regardless of the block size. That is, a probability table is prepared according to the maximum block size. Here, assuming that the maximum block size is 8 × 8, 63 probability tables are used for each of the SIG bits and the LAST bits. The first 15 probability tables are used for 4 × 4 blocks, and the first 31 probability tables are used for 4 × 8 blocks and 8 × 4 blocks.

  As described above, the variable length coding method and the variable length decoding method of the present invention encode the number of significant coefficients of each block by the CAVLC method, and the size of the encoding target block and the size of the surrounding blocks. Are different from each other, the number of significant coefficients of the surrounding blocks is converted based on the ratio of the size of the encoding target block to the surrounding blocks, and the converted value is used to determine the variable length coding table. .

  With the operation as described above, even when the size of the encoding target block is different from the size of the surrounding blocks, the variable length table can be determined according to the size of the encoding target block. It is possible to improve the conversion efficiency.

  Also, the variable length coding method of the present invention uses the CABAC method to encode a bit (CBP bit) indicating whether each block has a significant coefficient or not. If the size is different, the presence / absence of a significant coefficient in the surrounding block is converted based on the ratio of the size of the encoding target block to the surrounding block, and the probability table used in the CABAC method is determined. Used for.

  With the operation as described above, even when the size of the encoding target block and the size of the surrounding blocks are different, the probability table can be determined according to the size of the encoding target block, Efficiency can be improved.

  The variable length coding method of the present invention uses a CABAC method to encode a bit indicating whether or not each coefficient in a block is a significant coefficient. Prepare a different set of probability tables for each block size. Alternatively, a probability table is prepared in accordance with the maximum block size of the encoding target block, and the same set of probability tables is used regardless of the difference in block size.

  By the operation as described above, even if a block has a plurality of sizes, it is possible to improve the coding efficiency by having a set of probability tables for each block size. In addition, by preparing a probability table according to the maximum block size and using the same set of probability tables regardless of the difference in block size, the number of probability tables can be reduced, and the memory size can be reduced. Can be small.

  In the present embodiment, a case has been described in which macroblocks are processed in units of horizontal 16 × vertical 16 pixels and motion compensation is processed in units of blocks of 16 × 16 to 4 × 4 pixels, but these units are different. The number of pixels may be sufficient.

  In the present embodiment, the case where the frequency conversion is processed in units of 8 × 8, 8 × 4, 4 × 8, or 4 × 4 blocks has been described. But it ’s okay.

  In the present embodiment, the case where the variable length coding table and the probability table are determined with reference to the blocks located on the left and the top as the peripheral blocks of the encoding target block has been described. The block may be another block. For example, there is a method using the upper right or upper left block or the like.

  In the present embodiment, the case of using the three variable length coding tables shown in FIG. 4 has been described in the description of the CAVLC method. However, the number of variable length coding tables and the configuration of the tables are described in FIG. It is not limited to. Further, the case where values such as N / 8 and N / 4 are used as threshold values for the number of significant coefficients of the peripheral blocks has been described, but these values may be other values. A different threshold may be used for each size of the encoding target block.

  In this embodiment, the case where the peripheral blocks are in the screen and in the same slice has been described. However, when these peripheral blocks do not satisfy this condition, only the peripheral blocks that satisfy the condition are used. Thus, the variable length coding table and the probability table may be determined.

(Embodiment 2)
Next, in the case where a frame structure or a field structure is mixed for each macroblock or MBP (macroblock pair; hereinafter referred to as MBP) with respect to the interlace signal, when moving picture coding and moving picture decoding are performed. A method for determining a context using the CAVLC method or the CABAC method will be described. Here, MBP is a unit in which two macroblocks adjacent in the vertical direction are combined, and a detailed configuration will be described later.

  FIG. 7 is a functional block diagram showing the configuration of the moving picture encoding apparatus according to the second embodiment. In the second embodiment, a block counter 701 is provided in addition to the configuration shown in the moving picture coding apparatus according to the first embodiment described above.

  The block counter 701 instructs the frame memory 101 to output in units of blocks to be subjected to variable-length encoding, and also instructs the code string generation unit 104 that the target block is an MBP boundary. Instruct whether or not. Further, the mode selection unit 109 determines whether the MBP is to be encoded with the frame structure or the field structure, and outputs the result to the code string generation unit 104. Based on the MBP boundary information output from the block counter 701 and the MBP structure information output from the mode selection unit 109, the code string generation unit 104 performs variable length encoding of the target block according to the second embodiment. Start it. The overall operation of the video encoding apparatus is the same as that described above.

  FIG. 8 is an explanatory diagram showing the relationship between the MBP data structure encoded with the frame structure and the MBP data structure encoded with the field structure. In the figure, white circles indicate pixels on odd horizontal scanning lines, and black circles hatched with diagonal lines indicate pixels on even horizontal scanning lines. When MBP is cut out from each frame representing an input image, as shown in the center of FIG. 8, pixels on odd horizontal scanning lines and pixels on even horizontal scanning lines are alternately arranged in the vertical direction. When such an MBP is encoded with a frame structure, the MBP is processed for each of two macroblocks 1 and 2. When encoding with a field structure, the MBP is divided into a macroblock MBt representing the top field and a macroblock MBb representing the bottom field when interlaced in the horizontal scanning line direction.

  FIG. 9 is a flowchart showing a large flow of calculation procedures when a context is determined by the CAVLC method according to the second embodiment and a corresponding VLC table is determined.

  Note that the positional relationship between blocks A and B, which are peripheral blocks of the encoding target block C, will be described as being the same as in FIG. The encoding target block C and the peripheral blocks A and B have a size of 4 × 4 pixels (coefficients), and the maximum value of the number of significant coefficients in each block will be described as 16. In addition, the number of significant coefficients of the peripheral block A located on the left of the encoding target block C is NL, and the number of significant coefficients of the peripheral block B positioned on the encoding target block C is NU.

  First, the code string generation unit 104 determines the number NL of significant coefficients of the target block A located to the left of the encoding target block C (step 901). Next, the number of significant coefficients NU of the target block B located above the encoding target block C is determined (step 902). Finally, by using these NL and NU, the significant coefficient of the target block is determined. The number N is determined (step 903).

  Note that N is determined by a method described later, and the VLC table corresponding to the value of N is determined as the VLC table used for the variable length code.

  Here, the relationship between the finally determined number N of significant coefficients and the VLC table is, for example, as shown in the table of FIG. Here, when the number N of significant coefficients is 0 to 2, the VLC0 table shown in FIG. 4 is used, and when the number N of significant coefficients is 3 to 10, the VLC table of VLC1 is used. When the number N of significant coefficients is 11 to 16, it is indicated that the VLC table of VLC2 is used.

  Hereinafter, a detailed procedure of each step in the flowchart shown in FIG. 9 will be described.

  FIG. 11 is a flowchart showing details of step 901 in FIG. 9, that is, the calculation procedure (two types (a) and (b)) for obtaining the number NL of significant coefficients of the peripheral block A.

  First, the first operation procedure will be described with reference to FIG. 11A. The code string generation unit 104 checks whether the peripheral block A located to the left of the encoding target block C is located in the same MBP (step S1). 1101) If they are within the same MBP, the two blocks are of the same type, so the number NL of significant coefficients of the peripheral block A is specified as NL = Num (A) (step 1104). Here, Num (x) indicates the number of significant coefficients of the block x. The type refers to a coding structure indicating whether a target block is coded with a field structure or a frame structure.

  If it is determined that the peripheral block A is not located in the same MBP, it is checked whether the peripheral block A is the same type of MBP as the target block C (step 1102). As a result, if the peripheral block A and the target block C are the same type of MBP, NL = Num (A) (step 1104). If the types are different, NL = (Num (A) It is calculated as + Num (A ′)) / 2 (step 1103). The peripheral block A ′ is a block corresponding to the block A, and the detailed positional relationship will be described later.

  Next, the second operation procedure will be described with reference to FIG. 11B. It is checked whether the peripheral block A located to the left of the encoding target block C is located in the same MBP (step 1101). If NL = Num (A) using the number of significant coefficients of the peripheral block A (step 1104), if it is determined that the peripheral block A is not located in the same MBP, the peripheral block A Is checked whether it is the same type of MBP as the target block C (step 1102). If the peripheral block A is the same type of MBP as the target block C, NL = Num (A) (step 1104), and if the types are different, NL = N · A (Not Available) ; Undefined) (step 1105).

  FIG. 12 is a diagram illustrating an example of the arrangement of the peripheral blocks A and A ′ when the encoding target block C has a field structure and a frame structure.

  FIG. 12A shows a case where the encoding target block C belongs to the MBP 1201 encoded with the field structure and the peripheral block A belongs to the MBP 1202 encoded with the frame structure. The peripheral block A ′ is located below the peripheral block A. This is because the correspondence is determined so that the scanning lines of the pixels belonging to each block are the same, as can be seen from the MBP having the frame structure and the field structure shown in FIG. That is, since the scanning lines belonging to the block C are distributed to the blocks A and A ′, the number of significant coefficients of the blocks A and A ′ is adopted as the NL used to determine the number of significant coefficients of the block C. ing.

  On the other hand, FIG. 12B shows a case where the encoding target block C belongs to the MBP 1203 encoded with the frame structure and the peripheral block A belongs to the MBP 1204 encoded with the field structure. The peripheral block A ′ is located at the same relative position in the MB located under the MB to which the peripheral block belongs. This is the same reason as in FIG. 12A, that is, since the scanning lines belonging to the block C are distributed to the blocks A and A ′, the NL used to determine the number of significant coefficients of the block C is This is because the number of significant coefficients of the blocks A and A ′ is employed.

  FIG. 13 is a flowchart for explaining the details of step 902 in FIG. 9, that is, the calculation procedure (two types (a) and (b)) for obtaining the number NU of the significant coefficients of the peripheral block B using the CAVLC method. .

  In FIG. 13A showing the first calculation procedure, the code string generation unit 104 checks whether a block or a macroblock located in the peripheral block B is located in the same MBP (step 1301). If they are located in the same MBP, these blocks are of the same type, so the number NU of the significant coefficients of the peripheral block B is set to NU = Num (B) (step 1305). If it is not located in the same MBP, it is checked whether the encoding target block C is a frame structure (step 1302). If it is not a frame structure but a field structure, then it is checked whether the peripheral block B has a frame structure (step 1303). If the peripheral block B has a frame structure, the number of significant coefficients of the peripheral block B As NU, NU = Num (B) (step 1305). If the peripheral block B has a field structure, the number Nu of significant coefficients is calculated as Nu = (Num (B) + Num (B ′)) / 2 (step 1308).

  If the target block C has the field structure, it is checked whether the peripheral block B has the field structure (step 1304). If the peripheral block B has the field structure, the number NU = Num (B ′) (step 1306). On the other hand, when the peripheral block B has a frame structure, the number Nu of significant coefficients is calculated as NU = Num (B) or NU = (Num (B) + Num (B ′)) / 2 (step 1307). Then, the process continues to step 803 through the steps.

  Further, in FIG. 13B showing the second calculation procedure, it is checked whether the block or macroblock located in the peripheral block B is located in the same MBP (step 1301). Since these blocks are the same type, NU = Num (B) is set as the number NU of the significant coefficients of the peripheral block B (step 1305). If it is not located in the same MBP, it is checked whether the encoding target block C is a frame structure (step 1302). If it is not a frame structure, then it is checked whether the peripheral block B is a frame structure (step 1302). Step 1303) When the peripheral block B has a frame structure, the number NU of significant coefficients is set to NU = NA · undefined (step 1305). If the peripheral block B has a field structure, the number of significant coefficients is calculated as Nu = (Num (B) + Num (B ′)) / 2 (step 1308). If the target block C has the field structure, it is checked whether the peripheral block B has the field structure (step 1304). If the peripheral block B has the field structure, the number NU = On the other hand, if the peripheral block B has a frame structure, the number Nu of significant coefficients is set to NU = NA (undefined) (step 1307), and the process continues to step 903. .

  FIG. 14 is a diagram illustrating an example of the arrangement of the peripheral blocks B and B ′ when the encoding target block C has a field structure and a frame structure.

  FIG. 14A shows a case where the encoding target block C belongs to the MBP 1401 encoded with the field structure and the peripheral block B belongs to the MBP 1402 encoded with the frame structure. The peripheral block B ′ is located on the peripheral block B. As can be seen from the frame structure and field structure MBP shown in FIG. 8, the field structure block C has two spatially continuous blocks B and B ′. Since they are the same, the number of significant coefficients of blocks B and B ′ is used as the NU used to determine the number of significant coefficients of block C. However, since there is no continuity between the block C and the block B ′ spatially, as shown in S1307, NU = Num (B) or NU = (Num (B) + Num (B ′)) / 2 and 2 The street calculation method can be considered.

  On the other hand, FIG. 14B shows a case where the encoding target block C belongs to the MBP 1401 encoded with the field structure, and the peripheral block B also belongs to the MBP 1403 encoded with the field structure. The peripheral block B ′ is located at the same relative position in the MB located above the MB to which the peripheral block B belongs. This is because the blocks C and B ′ belong to MBs encoded with the same type of field (top field / bottom field) structure, so that the block B is used as the NU used to determine the number of significant coefficients of the block C. This is because the number of significant coefficients of ′ is adopted.

  On the other hand, FIG. 14C shows a case where the encoding target block C belongs to the MBP 1404 encoded with the frame structure and the peripheral block belongs to the MBP 1403 encoded with the field structure. The peripheral block B ′ is located at the same relative position in the MB located above the MB to which the peripheral block B belongs. This is because the blocks B and B ′ have the same spatial position in MBP, and therefore the number of significant coefficients of the blocks B and B ′ is adopted as the NU used to determine the number of significant coefficients of the block C. Because.

  FIG. 15 is a flowchart showing details of step 903 in FIG. 9, that is, the VLC table determination procedure (two types (a) and (b)) according to the second embodiment.

  In FIG. 15A showing the first determination procedure, the code string generation unit 104 first uses the number N of significant coefficients of the encoding target block C and the number of significant coefficients NL and NU of the target blocks B and A. N = (NL + NU) / 2 is determined (step 1501). Next, it becomes possible to determine the VLC table using this N and the table shown in FIG. 10 (step 1502).

  In FIG. 15B showing the second determination procedure, the code string generation unit 104 first checks whether NL or NU is N · A (undefined) (step 1503), and determines whether NL, NU, Is undefined, for example, a default such as using a VLC table with N = 0 is adopted (step 1504). On the other hand, when only NU is undefined, N = NL is set, and the VLC corresponding to N is determined. If the table is determined (step 1505), and if only NL is undefined, N = NU, and the VLC table is determined based on N (step 1506), and neither NL nor NU is undefined In other words, when both NL and NU are determined, “others” is adopted and calculated as N = (NL + NU) / 2 to determine the VLC table (step 15). 07).

  Next, a procedure for determining a probability table used for the context of the CABAC scheme according to the second embodiment will be described.

  FIG. 16 is a flowchart showing a large flow of calculation procedures when a context is determined by the CABAC method according to the second embodiment and a corresponding probability table is determined. The code string generation unit 104 first determines the context value ctxA of the peripheral block A located to the left of the encoding target block C (step 1601), and then determines the surrounding block B positioned above the encoding target block C. The context value ctxB is determined (step 1602). Then, by using the values of ctxA and ctxB, the context value ctxC of the encoding target block C is determined (step 1603).

  Then, variable length coding is performed using a probability table corresponding to the determined context value ctxC.

  The detailed procedure of each step in the flowchart shown in FIG. 16 will be described below.

  FIG. 17 is a flowchart showing details of step 1601 in FIG. 16, that is, the calculation procedure (two types (a) and (b)) for obtaining the context value ctxA of the peripheral block A using the CABAC method. Here, the value that can be taken as the context value varies depending on what information (CBP bit, macroblock coding mode, reference picture number, differential quantization parameter, etc.) is handled. For example, when encoding CBP bits (bits indicating whether or not they have significant coefficients), the context is divided into 0 and 1 depending on the presence or absence of significant coefficients in each block. 1 and 0 if no significant coefficient is included. Therefore, the context value here corresponds to the presence or absence of a significant coefficient. In addition, when coding the coding mode of the macroblock, the context is divided into 0 and 1 depending on whether each block is a skip block or a block coded in the direct mode, respectively. The reference picture number and differential quantization parameter are divided into 0 and 1 depending on whether they are 0 or not.

  The first calculation procedure will be described with reference to FIG. 17A. The code string generation unit 104 checks whether the block or macroblock located in the peripheral block A is in the same MBP as the encoding target block C (step 1701). ). If within the same MBP, the context value ctxA of the peripheral block A is set to ctxA = ctx (A) (step 1704). Here, ctx (x) indicates the context value of the block x.

  If the peripheral block A is not in the same MBP as the encoding target block C, it is checked whether the peripheral block A is the same type of MBP as the encoding target block C (step 1702). In this case, if the types have the same structure, the context value ctxA of the peripheral block A is set to ctxA = ctx (A) (step 1704). On the other hand, when the peripheral block A and the target block C are different types of blocks, the context value ctxA = F1 (ctx (A), ctx (A ′)) is used as the context value ctxA of the peripheral block A. Calculate (step 1703). Here, F1 is a function that performs some arithmetic operation, for example, F1 (a, b) = a + b, a + 2b, a & b. Then, the process continues to step 1602.

  Then, the second operation procedure will be described with reference to FIG. 17B. It is checked whether the block or macroblock located in the peripheral block A is in the same MBP as the encoding target block C (step 1701). If so, the context value ctxA of the peripheral block A is set to ctxA = ctx (A) (step 1704). If the peripheral block A is not in the same MBP as the encoding target block C, the peripheral block A is encoded. It is checked whether the MBP has the same type as that of the block C to be converted (step 1702). In this case, if the type is the same structure, the context value ctxA of the peripheral block A is ctxA = ctx (A) (step 1704), while the peripheral block A and the target block C are different types of blocks. If there is, the context value ctxA is set to a default value (step 1705). This default value is one of the values that the context value can take, for example, 0 or 1.

  FIG. 18 is a flowchart showing details of step 1602 in FIG. 16, that is, the calculation procedure (two types (a) and (b)) for obtaining the context value of the peripheral block B using the CABAC method.

  In FIG. 18A showing the first calculation procedure, first, the code string generation unit 104 checks whether the block or macroblock located in the peripheral block B is MBP (step 1801). When located in the same MBP, the context value ctxB = ctx (B) is set (step 1805). If the target block C is not located in the same MBP as the neighboring block B, it is checked whether the target block C has a frame structure (step 1802). As a result, if the target block C has a frame structure, it is checked whether the peripheral block B has a frame structure (step 1803). If the peripheral block B has a frame structure, the context value ctxB = ctx (B) is set (step 1805). On the other hand, when the target block C has a frame structure and the peripheral block B has a field structure, the context value ctxB = F1 (ctx (B), ctx (B ′)) is set (step 1808).

  If the target block C has a field structure, it is next checked whether the peripheral block B has a field structure (step 1804). If the peripheral block B has a field structure, the context value ctxB = ctx (B ′) is set (step 1806). When the target block C has a field structure and the peripheral block B has a frame structure, the context value ctxB = ctx (B) or ctxB = F1 (ctx (B), ctx (B ′)) is set. (Step 1807). Here, the processing of F1 is the same as described above. Then, the process continues to step 1603 through the steps.

  FIG. 19 is a flowchart showing details of step 1603 in FIG. 16, that is, the determination procedure of the probability table according to the second embodiment.

  In FIG. 19, the code string generation unit 104 is a step subsequent to FIG. 18, and first sets the context value of the encoding target block C to ctxC = F2 (ctx (A), ctx (B)) (step 1901). ). Here, F2 is a function that performs some kind of arithmetic operation in the same manner as F1, and is, for example, F2 (a, b) = a + b, a + 2b, a & b, a, b. Next, a probability table can be determined by using this ctxC (step 1902).

  Note that in the video decoding as well as the video encoding described above, the VLC table determination method in the CAVLC method and the context determination method in the CABAC method are operations in the variable length decoding unit 311 shown in FIG. The same operation as that of the code string generation unit 104 is performed. Here, in the variable length decoding unit 311, whether the block is an MBP boundary or not, and MBP is encoded with any structure of a frame or a field, which is necessary when determining a VLC table and a context. Information indicating whether or not the code string has been processed is obtained from the code string analysis unit 301.

  As described above, in the variable length coding method and the variable length decoding method according to Embodiment 2, information on significant coefficients of a plurality of peripheral blocks is used when the CAVLC method or the CABAC method is used. Therefore, it is possible to realize a method of selecting a VLC table or a probability table that improves the coding efficiency more effectively. In the second embodiment, it is needless to say that the structure type of the macroblock can be mutually converted into a frame structure and a field structure for each MBP. In addition, the unit for selecting either the frame structure or the field structure may not be MBP, and may be a macro block, for example.

  In the present embodiment, after obtaining the number or context of significant coefficients of the block located on the left side of the block to be encoded or decoded in the form described using FIG. 9 and FIG. Although the case where the number of significant coefficients or the context of the block located above the decoding target block is obtained has been described, the order of these may be reversed, and the determination result of S903 in FIG. 9 and S1603 in FIG. Has no effect.

  Further, application examples of the variable length coding method and variable length decoding method shown in the above embodiment and a system using the same will be described.

  FIG. 20 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. 20, 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.

  Further, the streaming server ex103 is connected from the camera ex113 through the base station ex109 and the telephone network ex104, and live distribution based on the encoded data transmitted by the user using the camera ex113 can be performed. 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 116 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 image encoding / decoding software may be incorporated into any storage medium (CD-ROM, flexible disk, hard disk, etc.) 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.

The variable length encoding device or variable length decoding device described in the above embodiments may be used for encoding and decoding of each device constituting this system.
A mobile phone will be described as an example.

  FIG. 21 is a diagram showing the mobile phone ex115 using the variable length coding method and the variable length 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 signal 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 conversion into a signal, this 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 has a configuration including the image encoding device described in the present invention, and an encoding method using the image data supplied from the camera unit ex203 in the image encoding device described in the above embodiment. The encoded image data is converted into encoded image data by compression encoding, and 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 receiving data of a moving image file linked to a home page or the like in the data communication mode, the received signal 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 the multiplexed data received via the antenna ex201, the demultiplexing unit ex308 separates the multiplexed data to generate an encoded bitstream of image data and an encoded bitstream of audio data. The encoded image data is supplied to the image decoding unit ex309 via the synchronization 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 image decoding device described in the present invention, and a decoding method corresponding to the encoding method described in the above embodiment for an encoded bit stream of image data. To generate playback moving image data, which 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 an analog audio signal, and then supplies the analog audio signal 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

  Note that the present invention is not limited to the above-described system, and recently, digital broadcasting by satellite and terrestrial has become a hot topic. As shown in FIG. Any of the decoding devices can be incorporated. Specifically, in the broadcasting station ex409, the encoded bit stream of the video information is transmitted to the 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 encoded bit stream and reproduces it. In addition, the image decoding apparatus described in the above embodiment can also be implemented in a playback apparatus ex403 that reads and decodes an encoded bitstream recorded on a storage medium ex402 such as a CD or DVD that is a recording medium. is there. In this case, the reproduced video signal is displayed on the monitor ex404. Further, a configuration in which an image decoding device 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 the monitor ex408 of the television is also conceivable. At this time, the image 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.

  Further, the image signal can be encoded by the image encoding device 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 image decoding device described 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.

  The configuration of the car navigation ex 413 is, for example, the configuration shown in FIG. 22 excluding the camera unit ex203, the camera interface unit ex303, and the image encoding unit ex312. 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 mounting formats: a transmitting terminal having only an encoder and a receiving terminal having only a decoder. Can be considered.

  As described above, the variable-length encoding method or the variable-length decoding method shown in the above embodiment can be used in any of the above-described devices / systems, and as a result, described in the above embodiment. An effect can be obtained.

Block diagram for describing an embodiment of the present invention Schematic diagram for explaining an embodiment of the present invention Block diagram for describing an embodiment of the present invention Schematic diagram for explaining an embodiment of the present invention and a conventional example Schematic diagram for explaining a conventional example Schematic diagram for explaining a conventional example Functional block diagram showing the configuration of the video encoding apparatus according to the second embodiment Explanatory drawing which shows the relationship between the data structure of MBP encoded with the frame structure which concerns on Embodiment 2, and the data structure of MBP encoded with a field structure The flowchart which shows the big flow of the calculation procedure in the case of determining a context with the CAVLC system which concerns on Embodiment 2, and determining a corresponding VLC table. Table illustrating the relationship between the number of significant coefficients and the VLC table according to the second embodiment The flowchart which shows the detail of the calculation procedure (two types of (a) and (b)) which calculates | requires the number NL of the significant coefficients of the surrounding block A which concerns on Embodiment 2. FIG. The figure which shows an example of arrangement | positioning of the surrounding blocks A and A 'in case the encoding object block C which concerns on Embodiment 2 is a field structure and a frame structure. The flowchart explaining the detail of the calculation procedure (two types of (a) and (b)) which calculates | requires the number NU of the significant coefficient of the surrounding block B using the CAVLC system which concerns on Embodiment 2. FIG. The figure which shows an example of arrangement | positioning of the surrounding blocks B and B 'in case the encoding object block C which concerns on Embodiment 2 is a field structure and a frame structure. The flowchart which shows the detail of the determination procedure (two types of (a) and (b)) of the VLC table which concerns on this Embodiment 2. The flowchart which shows the big flow of the calculation procedure in the case of determining a context with the CABAC system which concerns on Embodiment 2, and determining a corresponding probability table. The flowchart which shows the detail of the calculation procedure (two types of (a) and (b)) which calculates | requires the context value ctxA of the surrounding block A using the CABAC system which concerns on Embodiment 2. FIG. The flowchart which shows the detail of the calculation procedure (two types of (a) and (b)) which calculates | requires the context value of the surrounding block B using the CABAC system which concerns on Embodiment 2. FIG. The flowchart which shows the detail of the determination procedure of the probability table which concerns on this Embodiment 2. Block diagram showing the overall configuration of the content supply system Example of mobile phone using moving picture coding method and moving picture decoding method Mobile phone block diagram Example of digital broadcasting system Reference diagram showing how to calculate a conventional probability table

Explanation of symbols

101, 107 Frame memory 102 Difference calculation unit 103 Prediction error encoding unit 104 Code string generation unit 105 Prediction error decoding unit 106 Addition calculation unit 108 Motion vector detection unit 109 Mode selection unit 701 Block counter MBP Macroblock pair

Claims (8)

A variable length encoding method used when an image is divided into a plurality of blocks and encoding is performed in units of the blocks,
A variable length coding table used when coding the information of the encoding target block is determined according to the information of the peripheral blocks of the encoding target block, and the sizes of the encoding target block and the peripheral blocks are determined. When different, the variable length coding method is characterized in that the information of the neighboring blocks is converted into the size of the block to be coded and used.   2. The variable length coding method according to claim 1, wherein the information is the number of significant coefficients of the block. When the size of the encoding target block is larger than the size of the peripheral block, a plurality of sets of the peripheral blocks having a size equal to the size of the encoding target block are specified, and information on the peripheral block is obtained. 2. The variable length coding method according to claim 1, wherein a sum of the number of significant coefficients in a set of the plurality of specified peripheral blocks is used. When the size of the encoding target block is smaller than the size of the peripheral block, as the peripheral block information, the ratio of the size of the encoding target block to the peripheral block is a significant coefficient in the peripheral block. 2. The variable length coding method according to claim 1, wherein the number is used by multiplying the number. A variable length decoding method used when dividing an image into a plurality of blocks and performing decoding in units of the blocks,
A variable length decoding table used when decoding the information of the decoding target block is determined according to the information of the peripheral block of the decoding target block, and the size of the decoding target block and the peripheral block is determined. When different, the variable length decoding method is characterized in that the information of the neighboring blocks is converted into the size of the decoding target block and used. 6. The variable length decoding method according to claim 5, wherein the information is the number of significant coefficients of the block. When the size of the block to be decoded is larger than the size of the peripheral block, a plurality of sets of the peripheral blocks having a size equal to the size of the block to be decoded is specified, and information on the peripheral block 6. The variable length decoding method according to claim 5, wherein a sum of the number of significant coefficients in a set of the plurality of specified peripheral blocks is used. When the size of the decoding target block is smaller than the size of the peripheral block, as the peripheral block information, the ratio of the size of the decoding target block to the peripheral block is a significant coefficient in the peripheral block. 6. The variable length decoding method according to claim 5, wherein the number is multiplied and used.

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