JP2006187039A - Motion picture coding method and motion picture decoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motion picture coding method and a motion picture decoding method, that can avoid degradation in the coding efficiency of B-pictures, even when the number of the B-pictures inserted into between I-pictures or P-pictures increases, and the coding efficiency in direct mode can be made to improve. <P>SOLUTION: This method is provided with a coding control section 110 which preferentially determines pictures which becomes farthest from a previously coded picture, and rearranges each picture into the order to be encoded, when the coding order of a plurality of consecutive B-pictures located between I-pictures or P-pictures is considered in the display time order. Further, the method is provided with a mode selection section 109, which generates a movement vector of a block to be coded by performing the scaling to a forward movement vector, when coding in a direct mode is performed, in case of coding a block in the backward reference picture of a picture to be coded, and co-located with the block to be coded, when the forward motion vector has been used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a moving picture coding method and a moving picture decoding method, and in particular, a method of performing inter picture predictive coding processing and inter picture predictive decoding processing using a processed picture as a reference picture for a processing target picture. It is about.

  In the moving image encoding process, the amount of information is generally compressed using redundancy in the spatial direction and temporal direction of a moving image. Here, generally, as a method of using redundancy in the spatial direction, conversion to the frequency domain is used, and as a method of using redundancy in the temporal direction, inter-picture predictive encoding processing is used. In the inter-picture predictive coding process, when a certain picture is coded, a coded picture that is forward or backward in display time order with respect to the coding target picture to be coded is coded. A reference picture corresponding to the target picture is used. Then, the amount of motion of the encoding target picture relative to the reference picture is detected, and a time is obtained by taking a difference between the image data obtained by performing the motion compensation processing based on the amount of motion and the image data of the encoding target picture. Remove direction redundancy. Further, the amount of information for the encoding target picture is compressed by removing the redundancy in the spatial direction from the difference value.

  H. currently being standardized. In a moving picture coding scheme called H.264, a picture that does not perform inter-picture predictive coding processing, that is, performs intra-picture coding processing is called an I picture. In addition, a picture that is subjected to inter-picture prediction encoding with reference to one picture that has already been processed in front of or behind the encoding target picture in display time order is called a P picture, and the encoding target picture in display time order A picture that is subjected to inter-picture predictive coding with reference to two processed pictures that are already processed in front or behind is called a B picture (for example, see Non-Patent Document 1).

  FIG. 20 (a) is a diagram showing the relationship between each picture and the corresponding reference picture in the above moving picture coding system, and FIG. 20 (b) shows the order of the code strings generated by the coding. FIG.

  The picture I1 is an I picture, the pictures P5, P9, and P13 are P pictures, and the pictures B2, B3, B4, B6, B7, B8, B10, B11, and B12 are B pictures. That is, the P pictures P5, P9, and P13 are subjected to inter-picture prediction encoding using the I picture I1, the P picture P5, and the P picture P9 as reference pictures, respectively, as indicated by arrows.

  In addition, as shown by arrows, B pictures B2, B3, and B4 are subjected to inter-picture prediction coding using I picture I1 and P picture P5 as reference pictures, and B pictures B6, B7, and B8 are respectively As shown by the arrows, P pictures P5 and P pictures B9 are used as reference pictures and subjected to inter-picture prediction coding, and B pictures B10, B11, and B12 are respectively P pictures as shown by the arrows. Inter-picture predictive coding is performed using P9 and P picture P13 as reference pictures.

  In the above encoding, a picture used as a reference picture is encoded before a picture that refers to the picture. Therefore, the code sequence generated by the above encoding has the picture order as shown in FIG.

H. In the H.264 moving image coding method, a coding mode called a direct mode can be selected for coding a B picture. The inter-frame prediction method in the direct mode will be described with reference to FIG. FIG. 21 is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this case, the motion vector c used when the block b located at the same position as the block a in the picture P9, which is the reference picture behind the picture B6, 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 a motion vector parallel to the motion vector c to obtain a reference block from the picture P5 which is a forward reference picture and the picture P9 which is a backward reference picture, and performs bi-directional prediction and performs coding. Is done. That is, the motion vector used when coding the block a is the motion vector d for the picture P5 and the motion vector e for the picture P9.
ISO / IEC 14496-2 “Information technology − Coding of audio-visualobjects − Part2: Visual” pp.218-219

  However, when the inter-picture predictive encoding process that refers to the I picture or P picture is performed on the B picture as described above, the temporal distance between the encoding target picture and the reference picture may become long. In such a case, the encoding efficiency is reduced. Especially when the number of inserted B pictures increases, that is, when the number of B pictures arranged between adjacent I and P pictures or between two nearest P pictures increases, The decrease is remarkable.

  Therefore, the present invention has been made to solve the above problems, and even when the number of B pictures inserted between I pictures and P pictures or between P pictures increases, An object of the present invention is to provide a moving picture coding method and a moving picture decoding method capable of avoiding deterioration in coding efficiency of a B picture. It is another object of the present invention to provide a moving picture coding method and a moving picture decoding method that can improve coding efficiency in the direct mode.

  In order to achieve the above object, a moving picture decoding method according to the present invention is a moving picture decoding method for decoding a code string generated by encoding image data corresponding to each picture constituting a moving picture. Then, when decoding the decoding target block, the motion vector of the same position block that is in the already decoded picture and is also in the same position as the decoding target block is used. And determining a motion vector of the decoding target block based on the motion vector of the decoding target block and a reference picture corresponding to the motion vector of the decoding target block. And a decoding step for decoding with motion compensation.

  The moving picture encoding method according to the present invention is a moving picture encoding method for generating a code string by encoding image data corresponding to each picture constituting a moving picture, and is a target to be encoded. The picture is an I picture having only a block for performing intra-picture coding, a P picture having a block for performing inter-picture predictive coding by one-way reference using an already coded picture as a first reference picture, and already coding A coding step of performing coding as one of B pictures having a block for performing inter-picture predictive coding by bi-directional reference using a completed picture as a first reference picture and a second reference picture, Indicates the encoding order of a plurality of consecutive B pictures sandwiched between the I picture or P picture at the time of display. Characterized in that it comprises a control step of determining a different order than the order.

  As a result, when encoding a B picture, a neighboring picture can be used as a reference picture in the order of display time, so that the prediction efficiency in motion compensation can be improved and the encoding efficiency can be improved. it can.

  The moving picture encoding method according to the present invention is a moving picture encoding method for generating a code string by encoding image data corresponding to each picture constituting a moving picture, and is a target to be encoded. A coding step of coding a picture as a B picture having a block for performing inter-picture predictive coding by bi-directional reference using at least a picture that has already been coded as a first reference picture and a second reference picture In the encoding step, as a direct mode for performing motion compensation on the encoding target block of the B picture that is the encoding target based on the motion vector of the already encoded block based on the motion vector of the encoding target block When encoding, the block in the second reference picture at the same position as the encoding target block is used. The encoding target block by scaling the first motion vector based on the first reference picture referenced by the block used when encoding the image using a difference in information indicating the display order of the pictures. It is characterized in that a motion vector for motion compensation is obtained.

  As a result, when the direct mode is selected, the first motion vector of the second reference picture is scaled, so that it is not necessary to add motion vector information to the code string, and the prediction efficiency is improved. be able to.

  In addition, when the encoding target block of the B picture that is the encoding target is encoded as the direct mode, it was used when the block in the second reference picture at the same position as the encoding target block was encoded The second motion vector based on the second reference picture referred to by the block is scaled by using a difference in information indicating the display order of the pictures, thereby obtaining a motion vector for motion compensation of the encoding target block. May be obtained.

  As a result, when the direct mode is selected, scaling is performed on the second motion vector of the second reference picture, so that it is not necessary to add motion vector information to the code string and the prediction efficiency is improved. be able to.

  In addition, when the encoding target block of the B picture that is the encoding target is encoded as the direct mode, the block in the second reference picture at the same position as the encoding target block is encoded in the direct mode. The difference in information indicating the display order of pictures with respect to the first motion vector based on the first reference picture referenced by the block substantially used when coding the block in the second reference picture. By performing scaling using, a motion vector for motion compensation of the encoding target block may be obtained.

  Accordingly, when the direct mode is selected, the scaling is performed on the first motion vector substantially used in the second reference picture, so that it is not necessary to add motion vector information to the code string, and Prediction efficiency can be improved.

  In addition, when the encoding target block of the B picture to be encoded is encoded as the direct mode, the block used when the block in the backward P picture at the same position as the encoding target block is encoded The first motion vector based on the first reference picture that is referenced by is scaled using a difference in information indicating the display order of pictures to obtain a motion vector for motion compensation of the coding target block. May be.

  As a result, when the direct mode is selected, scaling is performed on the first motion vector of the backward P picture, so that it is not necessary to add motion vector information to the code string and improve prediction efficiency. Can do.

  Further, when the encoding target block of the B picture to be encoded is encoded as the direct mode, the block in the second reference picture at the same position as the encoding target block is based on at least the first reference picture. When the first motion vector is encoded, the block in the second reference picture at the same position with respect to the first motion vector includes only the second motion vector based on the second reference picture. The second motion vector is scaled by using a difference in information indicating the display order of pictures, thereby obtaining a motion vector for motion compensation of the encoding target block. May be obtained.

  Accordingly, when the direct mode is selected, if the second reference picture has the first motion vector, the first motion vector is scaled, and the second reference picture is the first motion picture. If there is only a second motion vector without a motion vector, the second motion vector is scaled, so there is no need to add motion vector information to the code string and the prediction efficiency is improved. Can be made.

  A moving picture decoding method according to the present invention is a moving picture decoding method for decoding a code string generated by encoding image data corresponding to each picture constituting a moving picture. A decoding step of performing inter-picture predictive decoding using a target picture that is already decoded as a reference picture, and in the decoding step, a picture that has already been decoded is a first reference picture When performing inter-picture predictive decoding using bi-directional reference used as the second reference picture, a code sequence including at least the closest picture in the display time order is decoded as the first reference picture and the second reference picture, respectively. It is characterized by that.

  As a result, when performing inter-picture predictive encoding processing by bi-directional reference, a code string generated by encoding using pictures located nearby in order of display time as the first reference picture and the second reference picture, When decrypting, the decryption process can be performed correctly.

  A moving picture decoding method according to the present invention is a moving picture decoding method for decoding a code string generated by encoding image data corresponding to each picture constituting a moving picture. A decoding step of performing inter-picture predictive decoding using a target picture that is already decoded as a reference picture, in which the decoding target picture has already been decoded It is a picture having a block for performing inter-picture predictive decoding by bi-directional reference using a picture as a first reference picture and a second reference picture, and a block to be decoded has already been decoded into a motion vector When decoding as a direct mode in which motion compensation is performed using a motion vector of the decoding target block, Indicates the display order of pictures for the first motion vector based on the first reference picture that is used when the block in the second reference picture located at the same position as the current block is decoded. By performing scaling using the information difference, a motion vector for motion compensation of the decoding target block is obtained.

  Thus, when the direct mode is selected, the first motion vector of the second reference picture is scaled, so that the decoding process can be correctly performed when decoding.

  Further, when the decoding target picture is a picture having a block for performing inter-picture predictive decoding by bi-directional reference and decoding is performed in the direct mode, the decoding target block is located at the same position as the decoding target block. The second motion vector based on the second reference picture referred to by the block used when the block in the second reference picture is decoded is scaled using a difference in information indicating the display order of the pictures. By performing this, a motion vector for motion compensation of the decoding target block may be obtained.

  Thus, when the direct mode is selected, the second motion vector of the second reference picture is scaled, so that the decoding process can be performed correctly when decoding.

  Further, when the decoding target picture is a picture having a block for performing inter-picture predictive decoding by bi-directional reference and decoding is performed in the direct mode, the decoding target block is located at the same position as the decoding target block. When a block in a certain second reference picture is decoded in the direct mode, it is based on the first reference picture referred to by the block substantially used in decoding the block in the second reference picture. A motion vector for motion compensation of the decoding target block may be obtained by performing scaling on the first motion vector using a difference in information indicating the display order of reference pictures.

  Accordingly, when the direct mode is selected, the first motion vector substantially used in the second reference picture is scaled, so that the decoding process can be correctly performed when decoding.

  In addition, when the decoding target picture is a picture having a block that performs inter-picture predictive decoding by bi-directional reference, and the decoding target block is decoded in the direct mode, the decoding target picture is positioned backward in display time order, The block used when a block located at the same position as the decoding target block in a picture to be subjected to inter-picture prediction decoding by one-way reference using a picture that has already been decoded as a first reference picture The first motion vector based on the first reference picture referenced by is scaled using a difference in information indicating the display order of pictures, thereby obtaining a motion vector for motion compensation of the decoding target block. May be.

  Thus, when the direct mode is selected, scaling is performed on the first motion vector of a picture to be subjected to inter-picture predictive decoding based on one-way reference, so that decoding processing is correctly performed when decoding. Can do.

  Note that the present invention can be realized not only as such a moving image encoding method and a moving image decoding method, but also including the characteristic steps included in such a moving image encoding method and a moving image decoding method. It can be realized as a moving image encoding device and a moving image decoding device provided as means. Further, it can be realized as a code string encoded by a moving image encoding method and distributed via a recording medium such as a CD-ROM or a transmission medium such as the Internet.

  As described above, according to the moving picture coding method of the present invention, when a B picture is coded, a neighboring picture can be used as a reference picture in the order of display time. Since the prediction efficiency is improved, the coding efficiency is improved.

  Further, in the direct mode, by performing scaling on the first motion vector of the second reference picture, it is not necessary to send motion vector information, and prediction efficiency can be improved.

  Further, in direct mode, by scaling the first motion vector substantially used in the direct mode of the second reference picture, there is no need to send motion vector information and the same in the second reference picture. Even when the position block is encoded in the direct mode, the prediction efficiency can be improved.

  In the direct mode, the second motion vector used when coding the block at the same position of the second reference picture is scaled, so that it is not necessary to send motion vector information and the second reference Even when the block at the same position in the picture has only the second motion vector, the prediction efficiency can be improved.

  In addition, by forcing the motion vector in the direct mode to be 0, when the direct mode is selected, it is not necessary to send motion vector information, and the motion vector scaling processing is unnecessary, reducing the processing amount. Can be achieved.

  In the direct mode, by scaling the motion vector of the backward P picture, when the second reference picture is a B picture, there is no need to store the motion vector of the B picture. Further, it is not necessary to send motion vector information, and the prediction efficiency can be improved.

  In the direct mode, if the second reference picture has the first motion vector, the first motion vector is scaled, and the second reference picture does not have the first motion vector. If there are only two motion vectors, the second motion vector is scaled, so there is no need to add motion vector information to the code string, and the prediction efficiency can be improved.

  Further, according to the moving picture decoding method according to the present invention, the pictures used as the first reference and the second reference when performing inter-picture prediction encoding processing using bi-directional prediction are located in the vicinity in the order of display time. When decoding a code string generated by encoding using a picture, a correct decoding process can be performed.

  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 an embodiment of a moving picture coding apparatus using a moving picture coding method according to the present invention.

  As shown in FIG. 1, the moving image encoding apparatus includes a rearrangement 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, and a reference. A picture memory 107, a motion vector detection unit 108, a mode selection unit 109, an encoding control unit 110, switches 111 to 115, and a motion vector storage unit 116 are provided.

  The rearrangement memory 101 stores moving images input in units of pictures in the order of display time. The encoding control unit 110 rearranges the pictures stored in the rearrangement memory 101 in the order in which encoding is performed. Also, the encoding control unit 110 controls the motion vector storage operation in the motion vector storage unit 116.

  The motion vector detection unit 108 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 mode selection unit 109 determines a macroblock coding mode using the motion vector detected by the motion vector detection unit 108, and generates predicted image data based on the coding mode. The difference calculation unit 102 calculates a difference between the image data read from the rearrangement memory 101 and the predicted image data input from the mode selection unit 109 to generate prediction error image data.

  The prediction error encoding unit 103 performs encoding processing such as frequency conversion and quantization on the input prediction error image data to generate encoded data. The code string generation unit 104 performs variable-length coding or the like on the input encoded data, and further, motion vector information, encoding mode information, and other related information input from the mode selection unit 109 Is added to generate a code string.

  The prediction error decoding unit 105 performs decoding processing such as inverse quantization and inverse frequency 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 error decoding unit 105 and the predicted image data input from the mode selection unit 109 to generate decoded image data. The reference picture memory 107 stores the generated decoded image data.

  FIG. 2 is an explanatory diagram of pictures and relative indexes. The relative index is used to uniquely identify the reference picture stored in the reference picture memory 107, and is a number associated with each picture as shown in FIG. The relative index is used to indicate a reference picture to be used when a block is encoded by inter picture prediction.

  FIG. 3 is a conceptual diagram of a video encoded signal format by the video encoding device. The coded signal Picture for one picture is composed of a header coded signal Header included at the head of the picture, a block coded signal Block1 in the direct mode, a block coded signal Block2 by inter-picture prediction other than the direct mode, and the like. Yes. In addition, an encoded signal Block2 of a block based on inter-picture prediction other than the direct mode includes a first relative index RIdx1 and a second relative index RIdx2 for indicating two reference pictures used for inter-picture prediction, a first motion vector MV1, The second motion vector MV2 is provided in this order. On the other hand, the block encoded signal Block1 in the direct mode does not have the first relative index RIdx1, the second relative index RIdx2, the first motion vector MV1, and the second motion vector MV2. Which of the first relative index RIdx1 and the second relative index RIdx2 is used can be determined by the prediction type PredType. Also, the first relative index RIdx1 indicates the first reference picture, and the second relative index RIdx2 indicates the second reference picture. That is, whether it is the first reference picture or the second reference picture is determined by the data position in the coded sequence.

  Note that a picture that is subjected to inter-picture predictive coding by one-way reference using a previously coded picture that is either before or after in display time order as a first reference picture is a P picture, and is in display time order. In this embodiment, a picture that performs inter-picture predictive coding by bi-directional reference using a picture that has already been coded as a first reference picture and a second reference picture, either in front or behind, is a B picture. In this embodiment, the first reference picture is described as a forward reference picture, and the second reference picture is described as a backward reference picture. The first motion vector and the second motion vector, which are motion vectors for the first reference picture and the second reference picture, will be described as a forward motion vector and a backward motion vector, respectively.

  Next, a method for assigning the first relative index and the second relative index will be described with reference to FIG.

  As the value of the first relative 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 relative 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 from the order close 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 from the order closest to the encoding target picture.

  For example, in FIG. 2A, when the first relative index RIdx1 is 0 and the second relative index Ridx2 is 1, the forward reference picture is a B picture with picture number 6, and the backward reference picture is picture number 9. P picture. Here, the picture number is a number indicating the display order.

  The relative index in the block is expressed by a variable-length code word, and a code having a shorter code length is assigned as the value is smaller. Normally, the picture closest to the encoding target picture is selected as the reference picture for inter-picture prediction. Therefore, if the relative index values are assigned in the order closest to the encoding target picture as described above, the encoding efficiency increases.

  On the other hand, by explicitly instructing using the buffer control signal (RPSL in the Header shown in FIG. 3) in the encoded signal, it is possible to arbitrarily change the allocation of the reference picture to the relative index. By changing the allocation, it is possible to make the reference picture whose second relative index is 0 as an arbitrary reference picture in the reference picture memory 107. For example, as shown in FIG. The assignment can be changed.

Next, the operation of the moving picture coding apparatus configured as described above will be described.
FIG. 4 is an explanatory diagram showing the order of pictures in the rearrangement memory 101, and is an explanatory diagram showing (a) the input order and (b) the rearrangement order. Here, the vertical line indicates a picture, and the symbol shown at the lower right of each picture is a picture in which the first alphabet indicates the picture type (I, P, or B), and the second and subsequent numbers indicate the display order. Numbers are shown.

  For example, as shown in FIG. 4A, the input image is input to the rearrangement memory 101 in units of pictures in order of display time. When a picture is input to the rearrangement memory 101, the encoding control unit 110 rearranges each picture input in the rearrangement memory 101 in the order in which encoding is performed. 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. .

  Here, it is assumed that the P picture refers to one nearby already encoded I or P picture that is forward or backward in display time order. In addition, it is assumed that the B picture refers to two neighboring encoded pictures that are forward or backward in display time order.

  The encoding order of the pictures is that B pictures between the two P pictures (three pictures in the example of FIG. 4 (a)) are coded from the picture at the center, and then the B picture close to the P picture is selected. Suppose you want to encode. For example, the pictures B6 to P9 are encoded in the order of pictures P9, B7, B6, and B8.

  In this case, in each of the pictures B6 to P9, the picture at the end point of the arrow shown in FIG. 4A refers to the picture at the start point of the arrow. That is, the picture B7 refers to the pictures P5 and P9, the picture B6 refers to the pictures P5 and B7, and the picture B8 refers to the pictures B7 and P9. In this case, the encoding control unit 110 rearranges the pictures in the order in which the encoding is performed as shown in FIG.

  Next, each picture rearranged in the rearrangement memory 101 is read out in units of motion compensation. Here, the unit of motion compensation is referred to as a macroblock, and the macroblock has a size of horizontal 16 × vertical 16 pixels. Hereinafter, the encoding processing of the pictures P9, B7, B6, and B8 shown in FIG.

<Encoding process of picture P9>
Since the picture P9 is a P picture, inter-picture prediction coding is performed with reference to one already processed picture that is forward or backward in display time order. In the coding of the picture P9, the reference picture is the picture P5 as described above. The picture P5 has already been encoded, and the decoded picture is stored in the reference picture memory 107. In encoding a P picture, the encoding control unit 110 controls each switch so that the switches 113, 114, and 115 are turned on. Thereby, the macroblock of the picture P9 read from the rearrangement 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 uses the decoded image data of the picture P5 stored in the reference picture memory 107 as a reference picture, and detects a motion vector for the macroblock of the picture P9. Then, the motion vector detection unit 108 outputs the detected motion vector to the mode selection unit 109.

  The mode selection unit 109 uses the motion vector detected by the motion vector detection unit 108 to determine the encoding mode of the macroblock of the picture P9. Here, the encoding mode indicates how the macroblock is encoded. In the case of a P picture, for example, any of an intra-picture encoding, an inter-picture predictive encoding using a motion vector, and an inter-picture predictive encoding not using a motion vector (treating motion as 0) is used. Decide whether to encode. In determining the coding mode, generally, a method is selected such that the coding error becomes smaller with a small amount of bits.

  The mode selection unit 109 outputs the determined encoding mode to the code string generation unit 104. At this time, when the coding mode determined by the mode selection unit 109 is inter-picture predictive coding, the motion vector used in the inter-picture predictive coding is output to the code string generation unit 104, Further, it is stored in the motion vector storage unit 116.

  Further, the mode selection 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. However, the mode selection unit 109 does not output predicted image data when intra-picture encoding is selected. The mode selection unit 109 controls the switch 111 to be connected to the a side and the switch 112 to the c side when the intra-picture encoding is selected, and when the inter-picture predictive encoding is selected. The switch 111 is controlled to be connected to the b side and the switch 112 is connected to the d side. Hereinafter, a case where inter-picture prediction coding is selected by the mode selection unit 109 will be described.

  The difference calculation unit 102 receives the macroblock image data of the picture P9 read from the rearrangement memory 101 and the predicted image data output from the mode selection unit 109. The difference calculation unit 102 calculates the difference between the image data of the macroblock of the picture P9 and the prediction image data, generates prediction error image data, and outputs the prediction error image data to the prediction error encoding unit 103.

  The prediction error encoding unit 103 performs encoding processing such as frequency conversion and quantization on the input prediction error image data to generate encoded data, and the code string generation unit 104 and the prediction error decoding To the unit 105. Here, frequency conversion and quantization processing are performed in units of horizontal 8 × vertical 8 pixels or horizontal 4 × vertical 4 pixels, for example.

  The code string generation unit 104 performs variable-length coding or the like on the input encoded data, and generates a code string by adding information such as a motion vector and a coding mode, header information, and the like, Output.

  On the other hand, the prediction error decoding unit 105 performs decoding processing such as inverse quantization or inverse frequency conversion on the input encoded data, generates decoded difference image data, and outputs the decoded difference image data to the addition operation unit 106. To do. The addition operation unit 106 generates decoded image data by adding the decoded differential image data and the predicted image data input from the mode selection unit 109, and stores the decoded image data in the reference picture memory 107.

  With the above processing, processing of one macroblock of the picture P9 is completed. By the same process, the encoding process is performed also on the remaining macroblocks of the picture P9. When the processing is completed for all the macroblocks of the picture P9, the encoding process for the picture B7 is performed next.

<Encoding process of picture B7>
In the reference image of picture B7, the forward reference picture is picture P5 and the backward reference picture is P9. Since the picture B7 is used as a reference picture when other pictures are encoded, the encoding control unit 110 controls each switch so that the switches 113, 114, and 115 are turned on. Therefore, the macroblock of the picture B7 read from the rearrangement memory 101 is 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 uses the decoded image data of the picture P5 stored in the reference picture memory 107 as the forward reference picture, the decoded image data of the picture P9 as the backward reference picture, and uses the macroblock of the picture B7. In contrast, the forward motion vector and the backward motion vector are detected. Then, the motion vector detection unit 108 outputs the detected motion vector to the mode selection unit 109.

  The mode selection unit 109 uses the motion vector detected by the motion vector detection unit 108 to determine the coding mode of the macroblock of the picture B7. Here, the B picture coding mode uses, for example, intra-picture coding, inter-picture predictive coding using forward motion vectors, inter-picture predictive coding using backward motion vectors, and two-way motion vectors. It is assumed that the selection can be made from the inter-picture predictive coding or the direct mode.

  Here, the operation in the case of encoding in the direct mode will be described with reference to FIG. FIG. 5 (a) is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B7 is encoded in the direct mode. In this case, the motion vector c used when the block b located at the same position as the block a in the picture P9 which is the reference picture behind the picture B7 is used. The motion vector c is stored in the motion vector storage unit 116. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and picture P9, which is a backward reference picture, using a motion vector obtained using motion vector c. For example, as a method of using the motion vector c, there is a method of generating a motion vector parallel to the motion vector c. The motion vector used when coding the block a in this case is the motion vector d for the picture P5 and the motion vector e for the picture P9.

  In this case, the magnitude of the motion vector d that is the forward motion vector is MVF, the magnitude of the motion vector e that is the backward motion vector is MVB, the magnitude of the motion vector c is MV, and the current picture (picture B7) The temporal distance between the backward reference picture (picture P9) and the picture (picture P5) referenced by the block of the backward reference picture is TRD, the current picture (picture B7) and the forward reference picture (picture P5). If the time distance between and is TRF, the magnitude MVF of the motion vector d and the magnitude MVB of the motion vector e are obtained by (Equation 1) and (Equation 2), respectively. The temporal distance between the pictures can be determined based on, for example, information indicating the display order (position) given to each picture or a difference between the information.

MVF = MV × TRF / TRD --- Formula 1
MVB = (TRF−TRD) × MV / TRD −−− Formula 2

  Here, MVF and MVB represent the horizontal and vertical components of the motion vector, respectively, and the positive and negative signs indicate the direction of the motion vector.

  In selecting an encoding mode, generally, a method is selected such that the encoding error is reduced with a small amount of bits. The mode selection unit 109 outputs the determined encoding mode to the code string generation unit 104. At this time, when the coding mode determined by the mode selection unit 109 is inter-picture predictive coding, the motion vector used in the inter-picture predictive coding is output to the code string generation unit 104, Further, it is stored in the motion vector storage unit 116. When the direct mode is selected, the motion vector used in the direct mode calculated by (Equation 1) and (Equation 2) is stored in the motion vector storage unit 116.

  Further, the mode selection 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. However, the mode selection unit 109 does not output predicted image data when intra-picture encoding is selected. In addition, when selecting intra-picture coding, the mode selection unit 109 controls the switch 111 to be connected to the a side and the switch 112 to the c side, and selects inter-picture predictive coding or direct mode. In this case, control is performed so that the switch 111 is connected to the b side and the switch 112 is connected to the d side. Hereinafter, a case where inter-picture predictive coding or direct mode is selected by the mode selection unit 109 will be described.

  The difference calculation unit 102 receives the macroblock image data of the picture B7 read from the rearrangement memory 101 and the predicted image data output from the mode selection unit 109. The difference calculation unit 102 calculates a difference between the image data of the macroblock of the picture B7 and the prediction image data, generates prediction error image data, and outputs the prediction error image data to the prediction error encoding unit 103.

  The prediction error encoding unit 103 performs encoding processing such as frequency conversion and quantization on the input prediction error image data to generate encoded data, and the code string generation unit 104 and the prediction error decoding To the unit 105.

  The code string generation unit 104 performs variable-length coding or the like on the input encoded data, and further generates and outputs a code string by adding information such as a motion vector and a coding mode.

  On the other hand, the prediction error decoding unit 105 performs decoding processing such as inverse quantization or inverse frequency conversion on the input encoded data, generates decoded difference image data, and outputs the decoded difference image data to the addition operation unit 106. To do. The addition operation unit 106 generates decoded image data by adding the decoded differential image data and the predicted image data input from the mode selection unit 109, and stores the decoded image data in the reference picture memory 107.

  With the above processing, processing of one macroblock of picture B7 is completed. The encoding process is performed on the remaining macroblock of the picture B7 by the same process. When all macroblocks in picture B7 are processed, the encoding process for picture B6 is next performed.

<Encoding process of picture B6>
Since the picture B6 is a B picture, inter-picture predictive encoding is performed with reference to two already processed pictures that are forward or backward in display time order. In the reference image of the picture B6, the forward reference picture is the picture P5 and the backward reference picture is B7 as described above. The picture B6 is not used as a reference picture when other pictures are encoded. Therefore, the encoding control unit 110 controls each switch so that the switch 113 is turned on and the switches 114 and 115 are turned off. Thereby, the macroblock of the picture B6 read from the rearrangement memory 101 is 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 uses the decoded image data of the picture P5 stored in the reference picture memory 107 as the forward reference picture, the decoded image data of the picture B7 as the backward reference picture, and the macroblock of the picture B6 In contrast, the forward motion vector and the backward motion vector are detected. Then, the motion vector detection unit 108 outputs the detected motion vector to the mode selection unit 109.

  The mode selection unit 109 uses the motion vector detected by the motion vector detection unit 108 to determine the encoding mode of the macroblock of the picture B6.

  Here, the operation in the case of using the direct mode for the macroblock of the picture B6 will be described with reference to FIG. 5B. FIG. 5B is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this case, the motion vector used when the block b at the same position as the block a in the picture B7, which is the reference picture behind the picture B6, is used. Here, it is assumed that the block b is encoded by only forward reference or two-way reference, and the forward motion vector is a motion vector c. It is assumed that the motion vector c is stored in the motion vector storage unit 116. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and picture B7, which is a backward reference picture, using a motion vector generated using motion vector c. For example, if a method for generating a motion vector parallel to the motion vector c is used as in the case of the picture B7, the motion vector used when coding the block a is the motion vector d, the picture for the picture P5. For B7, it becomes the motion vector e.

  In this case, the magnitude of the motion vector d that is the forward motion vector is MVF, the magnitude of the motion vector e that is the backward motion vector is MVB, the magnitude of the motion vector c is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture B7) and the picture (picture P5) referenced by the block b of the backward reference picture is TRD, the current picture (picture B6) and the forward reference picture (picture P5). ) Is a time distance from TRF, the magnitude MVF of the motion vector d and the magnitude MVB of the motion vector e are obtained by the above (formula 1) and (formula 2), respectively. Note that the temporal distance between pictures can be determined based on, for example, information indicating the display order given to each picture, or a difference between the information.

  In this way, by performing scaling on the forward motion vector of the B picture that is the backward reference picture in the direct mode, it is not necessary to send motion vector information and the motion prediction efficiency can be improved. Thereby, encoding efficiency can be improved. Furthermore, the encoding efficiency can be improved by using the nearest reference pictures in the order of display time as much as possible as the forward reference picture and the backward reference picture.

  Next, a second example in the case of using the direct mode will be described with reference to FIG. In this case, the motion vector used when the block b located at the same position as the block a in the picture B7 which is the reference picture behind the picture B6 is used. Here, it is assumed that the block b is encoded in the direct mode, and the forward motion vector substantially used at that time is the motion vector c. That is, the motion vector c is a motion vector obtained by scaling the motion vector used when coding the block i at the same position as the block b in the picture P9 that the picture B7 refers to backward. . As the motion vector c, the motion vector stored in the motion vector storage unit 116 is used, or the motion vector of the block i in the picture P9 used when the block b is encoded in the direct mode is used as the motion vector storage unit 116. Calculated by reading from. Note that the mode selection unit 109 stores only the forward motion vector when the motion vector obtained by the scaling process when the block b of the picture B7 is encoded in the direct mode in the motion vector storage unit 116. That's fine. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and backward reference picture B7, using a motion vector generated using motion vector c. For example, if a method for generating a motion vector parallel to the motion vector c is used as in the case of the first example, the motion vector used when coding the block a is the motion vector d for the picture P5. For the picture B7, the motion vector e is obtained.

  In this case, the magnitude MVF of the motion vector d, which is the forward motion vector for the block a, and the magnitude MVB of the motion vector e, which is the backward motion vector, are expressed in the same manner as in the first example of the direct mode. 1) and (Equation 2).

  In this way, in the direct mode, scaling is performed on the forward motion vector substantially used in the direct mode of the B picture which is the backward reference picture, so there is no need to send motion vector information and the backward reference Even when a block at the same position in a picture is encoded in the direct mode, the motion prediction efficiency can be improved. Thereby, encoding efficiency can be improved. Furthermore, encoding efficiency can be improved by using the nearest reference picture that can be used in the display time order as the forward and backward reference pictures.

  Next, a third example using the direct mode will be described with reference to FIG. FIG. 5C is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this case, the motion vector used when coding the block b in the same position as the block a in the picture B7 which is the reference picture behind the picture B6 is used. Here, it is assumed that the block b is encoded using only the backward motion vector, and the backward motion vector is the motion vector f. It is assumed that the motion vector f is stored in the motion vector storage unit 116. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and picture B7, which is a backward reference picture, using a motion vector generated using motion vector f. For example, if a method of generating a motion vector parallel to the motion vector f is used as in the case of the first example, the motion vector used when coding the block a is the motion vector g for the picture P5. For the picture B7, the motion vector is h.

  In this case, the magnitude of the motion vector g which is the forward motion vector is MVF, the magnitude of the motion vector h which is the backward motion vector is MVB, the magnitude of the motion vector f is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture B7) and the picture (picture P9) referenced by the block of the backward reference picture is TRD, the current picture (picture B6) and the forward reference picture (picture P5). , TRF, and TRB as the temporal distance between the current picture (picture B6) and the backward reference picture (picture B7), the magnitude MVF of the motion vector g and the magnitude MVB of the motion vector h Are obtained by (Equation 3) and (Equation 4), respectively.

MVF = −TRF × MV / TRD −−− Equation 3
MVB = TRB × MV / TRD −−− Equation 4

  Thus, in the direct mode, scaling is performed on the backward motion vector used when coding the block at the same position of the B picture which is the backward reference picture, so there is no need to send motion vector information, In addition, even when the block at the same position in the backward reference picture has only the backward motion vector, the prediction efficiency can be improved. Thereby, encoding efficiency can be improved. Furthermore, encoding efficiency can be improved by using the nearest reference picture that can be used in the order of display time as the forward and backward reference pictures.

  Next, a fourth example in the case of using the direct mode will be described with reference to FIG. FIG. 5 (d) is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this case, the motion vector used when coding the block b in the same position as the block a in the picture B7 which is the reference picture behind the picture B6 is used. Here, it is assumed that the block b is encoded using only the backward motion vector as in the third example, and the backward motion vector is the motion vector f. It is assumed that the motion vector f is stored in the motion vector storage unit 116. The block a performs bi-directional prediction from the picture P9 that is a picture to which the motion vector f refers and the picture B7 that is the backward reference picture by using the motion vector generated by using the motion vector f. For example, if a method for generating a motion vector parallel to the motion vector f is used as in the case of the first example, the motion vector used for encoding the block a is the motion vector g for the picture P9. For the picture B7, the motion vector is h.

  In this case, the magnitude of the motion vector g which is the forward motion vector is MVF, the magnitude of the motion vector h which is the backward motion vector is MVB, the magnitude of the motion vector f is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture B7) and the picture (picture P9) referenced by the block of the backward reference picture is TRD, the current picture (picture B6), and the backward reference picture (picture B7). ) Is a time distance from a picture (picture P9) referred to by a block, TRF, the magnitude MVF of the motion vector g and the magnitude MVB of the motion vector h are (Equation 1) and (Equation 2), respectively. Is required.

  Thus, in the direct mode, it is not necessary to send motion vector information by performing scaling on the backward motion vector used when coding the block at the same position of the B picture that is the backward reference picture. In addition, even when the block at the same position in the backward reference picture has only the backward motion vector, the prediction efficiency can be improved. Thereby, encoding efficiency can be improved. Furthermore, the coding efficiency can be improved by using the picture referenced by the backward motion vector as the forward reference picture and the nearest reference picture that can be used in the display time order as the backward reference picture. .

  Next, a fifth example in the case of using the direct mode will be described with reference to FIG. FIG. 6A is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this case, motion compensation is performed by setting the magnitude of the motion vector to 0, performing two-way reference using the picture P5 as the forward reference picture and the picture B7 as the backward reference picture.

  In this way, in the direct mode, by forcing the motion vector to 0, when the direct mode is selected, it is not necessary to send motion vector information, and the motion vector scaling processing is not required and the processing amount Can be reduced.

  Next, a sixth example in the case of using the direct mode will be described with reference to FIG. FIG. 6B is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this case, the motion vector g used when the block f at the same position as the block a in the picture P9 which is the P picture behind the picture B6 is used. The motion vector g is stored in the motion vector storage unit 116. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and picture B7, which is a backward reference picture, using a motion vector generated using motion vector g. For example, if a method of generating a motion vector parallel to the motion vector g is used as in the case of the first example, the motion vector used when coding the block a is the motion vector h for the picture P5. For the picture B7, the motion vector i is obtained.

  In this case, the magnitude of the motion vector h that is the forward motion vector is MVF, the magnitude of the motion vector i that is the backward motion vector is MVB, the magnitude of the motion vector g is MV, and the current picture (picture B6). On the other hand, the temporal distance between the P picture (picture P9) located backward in the display time order and the picture (picture P5) referred to by the block f of this P picture is TRD, and the current picture (picture B6). When the temporal distance from the forward reference picture (picture P5) is TRF and the temporal distance between the current picture (picture B6) and the backward reference picture (picture B7) is TRB, the magnitude MVF of the motion vector h The magnitude MVB of the motion vector i is obtained by (Expression 1) and (Expression 5), respectively.

  MVB = −TRB × MV / TRD −−− Formula 5

  In this way, in the direct mode, when the backward reference picture is a B picture, the motion vector of the B picture is stored by performing scaling on the motion vector of the P picture located backward in the display time order. There is no need to send motion vector information. Furthermore, encoding efficiency can be improved by using the nearest reference picture in display time order as the forward and backward reference pictures.

  Next, a seventh example when the direct mode is used will be described with reference to FIG. FIG. 6C is an explanatory diagram showing motion vectors in the direct mode, and shows a case where the block a of the picture B6 is encoded in the direct mode. In this example, the relative index assignment change (remapping) with respect to the picture number described above is performed, and the backward reference picture becomes the picture P9. In this case, the motion vector g used when the block f at the same position as the block a in the picture P9 which is the backward reference picture of the picture B7 is used. The motion vector g is stored in the motion vector storage unit 116. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and picture P9, which is a backward reference picture, using a motion vector generated using motion vector g. For example, if a method of generating a motion vector parallel to the motion vector g is used as in the case of the first example, the motion vector used when coding the block a is the motion vector h for the picture P5. For the picture P9, the motion vector i is obtained.

  In this case, the magnitude of the motion vector h that is the forward motion vector is MVF, the magnitude of the motion vector i that is the backward motion vector is MVB, the magnitude of the motion vector g is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture P9) and the picture (picture P5) referenced by the block of the backward reference picture is TRD, the current picture (picture B6) and the forward reference picture (picture P5). If the time distance between and is TRF, the magnitude MVF of the motion vector h and the magnitude MVB of the motion vector i are obtained by (Expression 1) and (Expression 2), respectively.

  In this way, even when the relative index assignment is changed for the picture number in the direct mode, the motion vector of the encoded picture can be scaled and the direct mode is selected. In such a case, there is no need to send motion vector information.

  When the block a of the picture B6 is encoded by the direct mode, the block at the same position as the block a in the backward reference picture of the picture B6 is encoded by the forward reference only, the two-way reference, or the direct mode. If the forward motion vector is used at the time of encoding, scaling is performed on the forward motion vector, as in the first example, the second example, or the seventh example. Block a is encoded in direct mode. On the other hand, if the block at the same position as the block a is encoded by only the backward reference, and the backward motion vector is used at the time of this encoding, the backward motion vector is scaled, As in the third example or the fourth example, the block a is encoded in the direct mode.

  The above direct mode is applicable not only when the time interval between frames is constant, but also when it is a variable frame interval.

  Mode selection section 109 outputs the determined encoding mode to code string generation section 104. Further, the mode selection unit 109 generates predicted image data based on the determined encoding mode, and outputs the predicted image data to the difference calculation unit 102. However, the mode selection unit 109 does not output predicted image data when intra-picture encoding is selected. In addition, when selecting intra-picture coding, the mode selection unit 109 controls the switch 111 to be connected to the a side and the switch 112 to the c side, and selects inter-picture predictive coding or direct mode. In this case, control is performed so that the switch 111 is connected to the b side and the switch 112 is connected to the d side. In addition, when the determined coding mode is inter-picture predictive coding, mode selecting section 109 outputs a motion vector used in the inter-picture predictive coding to code sequence generating section 104. Here, since the picture B6 is not used as a reference picture when other pictures are encoded, it is not necessary to store the motion vector used in the inter-picture prediction encoding in the motion vector storage unit 116. Hereinafter, a case where inter-picture predictive coding or direct mode is selected by the mode selection unit 109 will be described.

  The difference calculation unit 102 receives the macroblock image data of the picture B6 read from the rearrangement memory 101 and the predicted image data output from the mode selection unit 109. The difference calculation unit 102 calculates the difference between the image data of the macroblock of the picture B6 and the prediction image data, generates prediction error image data, and outputs the prediction error image data to the prediction error encoding unit 103. The prediction error encoding unit 103 generates encoded data by performing encoding processing such as frequency conversion and quantization on the input prediction error image data, and outputs the encoded data 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 further generates and outputs a code string by adding information such as a motion vector and a coding mode.

  With the above process, the encoding process for one macroblock of picture B6 is completed. The processing for the remaining macroblocks of picture B6 is performed in the same manner, and when it is completed, the encoding processing of picture B8 is performed.

<Encoding process of picture B8>
Since the picture B8 is a B picture, inter-picture predictive encoding is performed with reference to two already processed pictures that are forward or backward in display time order. In the reference image of this picture B8, the forward reference picture is picture B7 and the backward reference picture is P9 as described above. Since the picture B8 is not used as a reference picture when other pictures are encoded, the encoding control unit 110 controls each switch so that the switch 113 is turned on and the switches 114 and 115 are turned off. To do. Therefore, the macroblock of the picture B8 read from the rearrangement memory 101 is 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 uses the decoded image data of the picture B7 stored in the reference picture memory 107 as the forward reference picture, the decoded image data of the picture P9 as the backward reference picture, and uses the macroblock of the picture B8. In contrast, the forward motion vector and the backward motion vector are detected. Then, the motion vector detection unit 108 outputs the detected motion vector to the mode selection unit 109.

  The mode selection unit 109 uses the motion vector detected by the motion vector detection unit 108 to determine the encoding mode of the macroblock of the picture B8.

  Here, the operation when the direct mode is used for the macroblock of the picture B8 will be described with reference to FIG. FIG. 6 (d) 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, the motion vector used when coding the block b in the same position as the block a in the picture P9 which is the reference picture behind the picture B8 is used. Here, it is assumed that the block b is encoded by the forward reference, and the forward motion vector is a motion vector c. The motion vector c is stored in the motion vector storage unit 116. Block a performs bi-directional prediction from picture B7, which is a forward reference picture, and picture P9, which is a backward reference picture, using a motion vector generated using motion vector c. For example, if a method of generating a motion vector parallel to the motion vector c is used as in the case of the picture B7, the motion vector used when coding the block a is the motion vector d, the picture for the picture B7 For P9, this is the motion vector e.

  In this case, the magnitude of the motion vector d that is the forward motion vector is MVF, the magnitude of the motion vector e that is the backward motion vector is MVB, the magnitude of the motion vector c is MV, and the current picture (picture B8) The temporal distance between the backward reference picture (picture P9) and the picture (picture P5) referenced by the block b of the backward reference picture is TRD, the current picture (picture B8) and the forward reference picture (picture B7). ) And TB, and the temporal distance between the current picture (picture B8) and the backward reference picture (picture P9) is TRB, the magnitude MVF of the motion vector d and the magnitude MVB of the motion vector e Are obtained by (Equation 1) and (Equation 5), respectively.

  In this way, by performing scaling on the forward motion vector of the backward reference picture in the direct mode, it is not necessary to send motion vector information and the prediction efficiency can be improved. Thereby, encoding efficiency can be improved. Furthermore, the encoding efficiency can be improved by using the nearest reference pictures in the order of display time as much as possible as the forward reference picture and the backward reference picture.

  The direct mode is applicable not only when the time interval between frames is constant, but also when the time interval is variable.

  Mode selection section 109 outputs the determined encoding mode to code string generation section 104. Further, the mode selection unit 109 generates predicted image data based on the determined encoding mode, and outputs the predicted image data to the difference calculation unit 102. However, the mode selection unit 109 does not output predicted image data when intra-picture encoding is selected. Further, when selecting the intra-picture encoding, the mode selection unit 109 controls the switch 111 to be connected to the a side and the switch 112 to be connected to the c side, and selects the inter-picture predictive encoding or the direct mode. In this case, control is performed so that the switch 111 is connected to the b side and the switch 112 is connected to the d side. In addition, when the determined coding mode is inter-picture predictive coding, mode selecting section 109 outputs a motion vector used in the inter-picture predictive coding to code sequence generating section 104. Here, since the picture B8 is not used as a reference picture when other pictures are encoded, it is not necessary to store the motion vector used in the inter-picture prediction encoding in the motion vector storage unit 116. Hereinafter, a case where inter-picture predictive coding or direct mode is selected by the mode selection unit 109 will be described.

  The difference calculation unit 102 receives the macroblock image data of the picture B8 read from the rearrangement memory 101 and the predicted image data output from the mode selection unit 109. The difference calculation unit 102 calculates the difference between the image data of the macroblock of the picture B8 and the prediction image data, generates prediction error image data, and outputs the prediction error image data to the prediction error encoding unit 103. The prediction error encoding unit 103 generates encoded data by performing encoding processing such as frequency conversion and quantization on the input prediction error image data, and outputs the encoded data 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 further generates and outputs a code string by adding information such as a motion vector and a coding mode.

  With the above process, the encoding process for one macroblock of picture B8 is completed. Processing for the remaining macroblocks of picture B8 is performed in the same manner.

  Hereinafter, the encoding process of each picture is performed in the same manner as the pictures P9, B7, B6, and B8 by an encoding method according to the picture type of each picture and the position of the picture in the display time order.

  In the above embodiment, the operation of the moving picture coding method according to the present invention has been described by taking the case of using the picture prediction structure shown in FIG. 4A as an example. FIG. 10 is an explanatory diagram showing hierarchical picture prediction structures in this case. In FIG. 10, an arrow indicates a prediction relationship, and a picture at the end point of the arrow refers to a picture at the start point. In the picture prediction structure shown in FIG. 4 (a), when considered in display time order, the coding order is determined with priority given to the picture farthest from the already coded picture as shown in FIG. Yes. For example, the picture farthest from the I or P picture is a picture located at the center of consecutive B pictures. Therefore, for example, in a state where the pictures P5 and P9 have been encoded, the picture B7 becomes the next encoding target picture. Then, in a state where the pictures P5, B7, and P9 are already encoded, the pictures B6 and B8 are the next encoding target pictures.

  In addition, even when the picture prediction structure is different from those shown in FIGS. 4 and 10, the same method as the moving picture coding method according to the present invention can be used, and the effects of the present invention can be brought about. Examples of other picture prediction structures are shown in FIGS.

  FIG. 7 shows a case where the number of B pictures sandwiched between I or P pictures is 3, and the B pictures are encoded by selecting from the pictures closest to the already encoded pictures as the order of encoding. Show. FIG. 7 (a) is a diagram showing the prediction relationship of each picture shown in display time order, and FIG. 7 (b) is a diagram showing the picture order rearranged in the coding order (code string order). FIG. 11 is a hierarchical diagram of a picture prediction structure corresponding to FIG. In the picture prediction structure shown in FIG. 7 (a), when considered in order of display time, encoding is performed in order from the closest picture to the already encoded picture as shown in FIG. For example, in a state where the pictures P5 and P9 have been encoded, the pictures B6 and B8 are the next encoding target pictures. In a state where the pictures P5, B6, B8, and P9 have been encoded, the picture B7 becomes the next encoding target picture.

  FIG. 8 shows a case where the number of B pictures sandwiched between I or P pictures is 5, and the B picture is encoded with priority given to the picture farthest from the already encoded picture. FIG. 8A is a diagram showing the prediction relationship of each picture shown in the display time order, and FIG. 8B is a diagram showing the picture order rearranged in the coding order (code string order). FIG. 12 is a hierarchical diagram of a picture prediction structure corresponding to FIG. In the picture prediction structure shown in FIG. 8 (a), when considered in display time order, the coding order is determined by giving priority to a picture farthest from an already coded picture as shown in FIG. Yes. For example, the picture farthest from the I or P picture is a picture located at the center of consecutive B pictures. Therefore, for example, in a state where the pictures P7 and P13 have been encoded, the picture B10 becomes the next encoding target picture. In a state where the pictures P7, B10, and P13 have been encoded, the pictures B8, B9, B11, and B12 become the next encoding target pictures.

  FIG. 9 shows a case where the number of B pictures sandwiched between I or P pictures is 5, and the B picture is encoded with priority given to the picture closest to the already encoded picture. FIG. 9A is a diagram showing the prediction relationship of each picture shown in display time order, and FIG. 9B is a diagram showing the picture order rearranged in the coding order (code string order). FIG. 13 is a hierarchical diagram of a picture prediction structure corresponding to FIG. 9 (a). In the picture prediction structure shown in FIG. 9 (a), when considered in order of display time, encoding is performed in order from the closest picture to the already encoded picture as shown in FIG. For example, in a state where the pictures P5 and P9 have been encoded, the pictures B8 and B12 are the next encoding target pictures. In a state where the pictures P5, B8, B12, and P9 have been encoded, the pictures B9 and B11 become the next encoding target pictures. Further, in a state where the pictures P5, B8, B9, B11, B12, and P9 have been encoded, the picture B10 is the next encoding target picture.

  As described above, in the moving picture encoding method according to the present invention, when encoding a B picture for which inter picture predictive encoding processing is performed using bi-directional prediction, a plurality of B sandwiched between I or P pictures is encoded. The pictures are encoded in an order different from the display time order. In that case, pictures located in the vicinity in the order of display time as much as possible are used as forward and backward reference pictures. As the reference picture, when the B picture is available, the B picture is also used. Further, when encoding a plurality of B pictures sandwiched between I or P pictures in an order different from the display time order, the pictures are encoded in order from the picture farthest from the already encoded pictures. Alternatively, when encoding a plurality of B pictures sandwiched between I or P pictures in an order different from the display time order, the pictures are encoded in order from the picture that is closest to the already encoded picture.

  With such an operation, by using the moving picture coding method according to the present invention, when a B picture is coded, a neighboring picture can be used as a reference picture in the order of display time. Since the prediction efficiency at this time is improved, the coding efficiency can be improved.

  Further, in the moving picture coding method according to the present invention, when a picture coded as a B picture is referred to as a backward reference picture and a block in the B picture is coded in the direct mode, the backward reference picture When blocks at the same position are encoded by forward reference or two-way reference, a motion vector obtained by scaling the forward motion vector is used as a motion vector in the direct mode.

  In this way, by performing scaling on the forward motion vector of the B picture that is the backward reference picture in the direct mode, it is not necessary to send motion vector information and the prediction efficiency can be improved. Furthermore, the encoding efficiency can be improved by using the temporally nearest reference picture as the forward reference picture.

  Alternatively, when the block at the same position of the B picture which is the backward reference picture is encoded by the direct mode, the motion obtained by scaling the forward motion vector substantially used in the direct mode. The vector is used as a motion vector in the direct mode.

  In this way, in the direct mode, by scaling the forward motion vector substantially used in the direct mode of the B picture that is the backward reference picture, it is not necessary to send motion vector information and the backward direction. Even when the block at the same position in the reference picture is encoded in the direct mode, the prediction efficiency can be improved. Furthermore, the encoding efficiency can be improved by using the temporally nearest reference picture as the forward reference picture.

  Alternatively, when the block at the same position of the B picture that is the backward reference picture is encoded by backward reference, the motion vector obtained by scaling the backward motion vector is used as the motion vector in the direct mode. Used as

  Thus, in the direct mode, it is not necessary to send motion vector information by performing scaling on the backward motion vector used when coding the block at the same position of the B picture that is the backward reference picture. In addition, even when a block at the same position in the backward reference picture has only a backward motion vector, prediction efficiency can be improved. Furthermore, the encoding efficiency can be improved by using the temporally nearest reference picture as the forward reference picture.

  Alternatively, when the block at the same position of the B picture that is the backward reference picture is encoded by backward reference, the backward motion vector used at that time is referred to as a picture to which the backward motion vector refers. A motion vector obtained by scaling a backward reference picture as a reference picture is used as a motion vector in the direct mode.

  Thus, in the direct mode, it is not necessary to send motion vector information by performing scaling on the backward motion vector used when coding the block at the same position of the B picture that is the backward reference picture. In addition, even when the block at the same position in the backward reference picture has only the backward motion vector, the prediction efficiency can be improved. Thereby, encoding efficiency can be improved. Furthermore, the coding efficiency can be improved by using the picture referenced by the backward motion vector as the forward reference picture and the nearest reference picture that can be used in the display time order as the backward reference picture. .

Alternatively, in the direct mode, a motion vector having a size of 0 is forcibly used.
In this way, by forcing the motion vector in the direct mode to be 0, when the direct mode is selected, it is not necessary to send motion vector information, and the motion vector scaling processing is not required and the amount of processing is reduced. Reduction can be achieved.

  In the moving picture coding method of the present invention, a picture coded as a B picture is referred to as a backward reference picture, and the block in the B picture is positioned backward when coding using the direct mode. The motion vector obtained by scaling the forward motion vector used when the block at the same position in the P picture is encoded is used as the motion vector in the direct mode.

  In this way, in the direct mode, by scaling the motion vector of the backward P picture, when the backward reference picture is a B picture, there is no need to store the motion vector of the B picture, and It is not necessary to send motion vector information, and the prediction efficiency can be improved. Furthermore, the encoding efficiency can be improved by using the temporally nearest reference picture as the forward reference picture.

  In addition, when the relative index assignment to the picture number is changed and the block at the same position of the backward reference picture is encoded by forward reference, it is obtained by scaling the forward motion vector. The motion vector is used as a motion vector in the direct mode.

  As described above, in the direct mode, even when the allocation of the relative index to the picture number is changed, the motion vector of the encoded picture can be scaled, and the motion vector information can be changed. There is no need to send.

  In this embodiment, motion compensation is performed in units of 16 horizontal pixels × vertical 16 pixels, and encoding of a prediction error image is performed in units of horizontal 8 × vertical 8 pixels or horizontal 4 × vertical 4 pixels. However, these units may be different numbers of pixels.

  In this embodiment, the case where the number of consecutive B pictures is 3 or 5 has been described as an example. However, the number of B pictures may be another number.

  Also, in the present embodiment, the encoding mode of the P picture is selected from intra-picture encoding, inter-picture predictive encoding using a motion vector, and inter-picture predictive encoding not using a motion vector. Encoding modes include intra-picture encoding, inter-picture prediction encoding using forward motion vectors, inter-picture prediction encoding using backward motion vectors, inter-picture prediction encoding using two-way motion vectors, direct mode The case of selecting from the above has been described as an example, but these encoding modes may be other methods.

  In this embodiment, seven examples have been described in the direct mode. However, for example, one method uniquely determined for each macroblock or block may be used, or a block or macroblock may be used. One method may be selected from a plurality of methods every time. When a plurality of methods are used, information indicating which direct mode is used is described in the code string.

  In the present embodiment, the P picture is encoded by referring to one encoded I or P picture positioned forward or backward in the display time order, and the B picture is positioned forward or backward in the display time order. In the case of encoding with reference to two encoded pictures in the vicinity of the P picture, these are encoded pictures that are positioned forward or backward in display time order. Alternatively, a P picture is used as a reference picture candidate and is encoded with reference to at most one picture in each block. In the case of a B picture, a plurality of neighboring pictures that are located forward or backward in display time order May be used as reference picture candidates, and encoding may be performed with reference to a maximum of two pictures in each block.

  In addition, when the mode selection unit 109 stores the motion vector in the motion vector storage unit 116, if the target block is encoded by the bi-directional prediction or the direct mode, both the forward and backward motions are stored. Vectors may be stored, or only forward motion vectors may be stored. If only the forward motion vector is stored, the memory amount of the motion vector storage unit 116 can be reduced.

(Embodiment 2)
FIG. 14 is a block diagram showing a configuration of an embodiment of a moving picture decoding apparatus using the moving picture decoding method according to the present invention.

  As shown in FIG. 14, the moving picture decoding apparatus includes a code string analysis unit 1401, a prediction error decoding unit 1402, a mode decoding unit 1403, a frame memory control unit 1404, a motion compensation decoding unit 1405, a motion vector storage unit 1406, a frame A memory 1407, an addition operation unit 1408, and switches 1409 and 1410 are provided.

  The code string analysis unit 1401 extracts various data such as coding mode information and motion vector information from the input code string. The prediction error decoding unit 1402 decodes the prediction error encoded data input from the code string analysis unit 1401 to generate prediction error image data. The mode decoding unit 1403 controls the switches 1409 and 1410 with reference to the encoding mode information extracted from the code string.

  The frame memory control unit 1404 outputs the decoded image data stored in the frame memory 1407 as an output image based on information indicating the display order of pictures input from the code string analysis unit 1401.

  The motion compensation decoding unit 1405 performs decoding processing on the reference picture number and motion vector information, and acquires motion compensated image data from the frame memory 1407 based on the decoded reference picture number and motion vector. The motion vector storage unit 1406 stores a motion vector.

  The addition operation unit 1408 adds the prediction error encoded data input from the prediction error decoding unit 1402 and the motion compensated image data input from the motion compensation decoding unit 1405 to generate decoded image data. The frame memory 1407 stores the generated decoded image data.

  Next, the operation of the moving picture decoding apparatus configured as described above will be described. Here, it is assumed that the code sequence generated by the video encoding device is input to the video decoding device. That is, here, it is assumed that the P picture refers to one nearby processed I or P picture that is forward or backward in display time order. In addition, it is assumed that the B picture refers to two already-encoded neighboring pictures that are forward or backward in display time order.

  The pictures in the code string in this case are in the order shown in FIG. Below, the decoding process of the pictures P9, B7, B6, and B8 will be described in order.

<Decoding process of picture P9>
The code string of the picture P9 is input to the code string analysis unit 1401. The code string analysis unit 1401 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 1403. Also, the extracted motion vector information is output to the motion compensation decoding unit 1405. Further, the prediction error encoded data is output to the prediction error decoding unit 1402.

  The mode decoding unit 1403 controls the switches 1409 and 1410 with reference to the coding mode selection information extracted from the code string. When the coding mode selection is intra-picture coding, the mode decoding unit 1403 controls the switch 1409 to be connected to the a side and the switch 1410 to be connected to the c side. When the coding mode selection is inter-picture predictive coding, the mode decoding unit 1403 performs control so that the switch 1409 is connected to the b side and the switch 1410 is connected to the d side.

  The mode decoding unit 1403 also outputs information on coding mode selection to the motion compensation decoding unit 1405. Hereinafter, a case where the coding mode selection is inter-picture predictive coding will be described. The prediction error decoding unit 1402 decodes the input prediction error encoded data to generate prediction error image data. Then, the prediction error decoding unit 1402 outputs the generated prediction error image data to the switch 1409. Here, since the switch 1409 is connected to the b side, the prediction error image data is output to the addition operation unit 1408.

  The motion compensation decoding unit 1405 acquires motion compensated image data from the frame memory 1407 based on the input motion vector information and the like. The picture P9 has been encoded with reference to the picture P5, and the picture P5 has already been decoded and held in the frame memory 1407. Therefore, the motion compensation decoding unit 1405 acquires motion compensation image data from the image data of the picture P5 held in the frame memory 1407 based on the motion vector information. The motion compensated image data generated in this way is output to the addition operation unit 1408.

  Also, the motion compensation decoding unit 1405 stores motion vector information in the motion vector storage unit 1406 when decoding a P picture.

  The addition operation unit 1408 adds the input prediction error image data and motion compensation image data to generate decoded image data. The generated decoded image data is output to the frame memory 1407 via the switch 1410.

  As described above, the processing of one macroblock of the picture P9 is completed. By the same process, the remaining macroblocks are sequentially decoded. When all the macroblocks of the picture P9 are decoded, the picture B7 is decoded.

<Decoding process of picture B7>
Since operations up to the generation of the prediction error image data in the code string analysis unit 1401, the mode decoding unit 1403, and the prediction error decoding unit 1402 are the same as those in the decoding process of the picture P9, description thereof is omitted.

  The motion compensation decoding unit 1405 generates motion compensated image data based on the input motion vector information and the like. The picture B7 is encoded with reference to the picture P5 as a forward reference picture and with reference to P9 as a backward reference picture, and these pictures are already decoded and held in the frame memory 1407.

  When the mode selection is bi-prediction inter-picture predictive coding, the motion compensation decoding unit 1405 obtains forward reference image data from the frame memory 1407 based on the forward motion vector information. Further, backward reference image data is acquired from the frame memory 1407 based on the backward motion vector information. Then, the motion compensation decoding unit 1405 generates motion compensation image data by averaging the forward reference image data and the backward reference image data.

  When the mode selection is the direct mode, the motion compensation decoding unit 1405 acquires the motion vector of the picture P9 stored in the motion vector storage unit 1406. Then, the motion compensation decoding unit 1405 acquires the forward reference image data and the backward reference image data from the frame memory 1407 using the motion vector. Then, the motion compensation decoding unit 1405 generates motion compensation image data by averaging the forward reference image data and the backward reference image data.

  The case where the mode selection is the direct mode will be further described with reference to FIG. Here, it is assumed that the block a of the picture B7 is decoded, and the block of the picture P9 at the same position as the block a is a block b. The motion vector of the block b is a motion vector c, which refers to the picture P5. In this case, the motion vector d that refers to the picture P5 obtained using the motion vector c is used as the forward motion vector, and the motion that refers to the picture P9 obtained using the motion vector c is used as the backward motion vector. Use vector e. For example, as a method of using the motion vector c, there is a method of generating a motion vector parallel to the motion vector c. Image data obtained by averaging the forward reference data and the backward reference data obtained based on these motion vectors is defined as motion compensated image data.

  In this case, the magnitude of the motion vector d that is the forward motion vector is MVF, the magnitude of the motion vector e that is the backward motion vector is MVB, the magnitude of the motion vector c is MV, and the current picture (picture B7) The temporal distance between the backward reference picture (picture P9) and the picture (picture P5) referenced by the block b of the backward reference picture is TRD, the current picture (picture B7) and the forward reference picture (picture P5). )), The magnitude MVF of the motion vector d and the magnitude MVB of the motion vector e are obtained by (Expression 1) and (Expression 2), respectively. Here, MVF and MVB represent the horizontal component and the vertical component of the motion vector, respectively. The temporal distance between the pictures can be determined based on, for example, information indicating the display order (position) given to each picture or a difference between the information.

  The motion compensated image data generated in this way is output to the addition operation unit 1408. Also, the motion compensation decoding unit 1405 stores motion vector information in the motion vector storage unit 1406.

  The addition operation unit 1408 adds the input prediction error image data and motion compensation image data to generate decoded image data. The generated decoded image data is output to the frame memory 1407 via the switch 1410.

  As described above, the processing of one macroblock of the picture B7 is completed. By the same process, the remaining macroblocks are sequentially decoded. When all the macroblocks of the picture B7 are decoded, the picture B6 is decoded.

<Decoding process of picture B6>
Since operations up to the generation of the prediction error image data in the code string analysis unit 1401, the mode decoding unit 1403, and the prediction error decoding unit 1402 are the same as those in the decoding process of the picture P9, description thereof is omitted.

  The motion compensation decoding unit 1405 generates motion compensated image data based on the input motion vector information and the like. The picture B6 is encoded with reference to the picture P5 as the forward reference picture and with reference to B7 as the backward reference picture, and these pictures are already decoded and held in the frame memory 1407.

  When the mode selection is bi-prediction inter-picture predictive coding, the motion compensation decoding unit 1405 obtains forward reference image data from the frame memory 1407 based on the forward motion vector information. Further, backward reference image data is acquired from the frame memory 1407 based on the backward motion vector information. Then, the motion compensation decoding unit 1405 generates motion compensation image data by averaging the forward reference image data and the backward reference image data.

  When the mode selection is the direct mode, the motion compensation decoding unit 1405 acquires the motion vector of the picture B7 stored in the motion vector storage unit 1406. The motion compensation decoding unit 1405 acquires the forward reference image data and the backward reference image data from the frame memory 1407 using the motion vector. Then, the motion compensation decoding unit 1405 generates motion compensation image data by averaging the forward reference image data and the backward reference image data.

  A first example in which the mode selection is the direct mode will be described with reference to FIG. Here, it is assumed that the block a of the picture B6 is decoded, and the block of the picture B7 at the same position as the block a is a block b. The block b is assumed to have been inter-picture predictive coding by forward reference or inter-picture predictive coding by bi-directional reference, and the forward motion vector of the block b is a motion vector c. This motion vector c refers to the picture P5. In this case, the motion vector d referring to the picture P5 generated using the motion vector c is used as the forward motion vector for the block a, and the picture B7 generated using the motion vector c is used as the backward motion vector. A reference motion vector e is used. For example, as a method of using the motion vector c, there is a method of generating a motion vector parallel to the motion vector c. Image data obtained by averaging the forward reference image data and the backward reference image data obtained based on these motion vectors is defined as motion compensated image data.

  In this case, the magnitude of the motion vector d that is the forward motion vector is MVF, the magnitude of the motion vector e that is the backward motion vector is MVB, the magnitude of the motion vector c is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture B7) and the picture (picture P5) referenced by the block b of the backward reference picture is TRD, the current picture (picture B6) and the forward reference picture (picture P5). )), The magnitude MVF of the motion vector d and the magnitude MVB of the motion vector e are obtained by (Expression 1) and (Expression 2), respectively. The temporal distance between the pictures can be determined based on, for example, information indicating the display order (position) given to each picture or a difference between the information. Alternatively, the TRD and TRF values may be predetermined values determined for each picture. This predetermined value may be described in the code string as header information.

  A second example when the mode selection is the direct mode will be described with reference to FIG.

  In this case, the motion vector used when decoding the block b at the same position as the block a in the picture B7 which is the reference picture behind the picture B6 is used. Here, block b is assumed to have been encoded using the direct mode, and the forward motion vector substantially used at that time is referred to as motion vector c. As the motion vector c, the one stored in the motion vector storage unit 1406 is used, or the motion vector of the picture P9 used when the block b is encoded in the direct mode is read from the motion vector storage unit 1406. Find the scaling calculation. Note that the motion compensation decoding unit 1405 stores only the forward motion vector when the motion vector obtained by the scaling process when decoding the block b of the picture B7 in the direct mode is stored in the motion vector storage unit 1406. do it.

  In this case, the motion vector d referring to the picture P5 generated using the motion vector c is used as the forward motion vector for the block a, and the picture B7 generated using the motion vector c is used as the backward motion vector. A reference motion vector e is used. For example, as a method of using the motion vector c, there is a method of generating a motion vector parallel to the motion vector c. Image data obtained by averaging the forward reference image data and the backward reference image data obtained based on these motion vectors is defined as motion compensated image data.

  In this case, the magnitude MVF of the motion vector d that is the forward motion vector and the magnitude MVB of the motion vector e that is the backward motion vector are the same as in the first example of the direct mode (Equation 1), It can be determined using (Equation 2).

  Next, a third example when the mode selection is the direct mode will be described with reference to FIG.

  Here, it is assumed that the block a of the picture B6 is decoded, and the block of the picture B7 at the same position as the block a is a block b. It is assumed that the block b is subjected to backward reference predictive coding, and the backward motion vector of the block b is a motion vector f. This motion vector f refers to the picture P9. In this case, the motion vector g referring to the picture P5 obtained using the motion vector f is used as the forward motion vector for the block a, and the picture B7 obtained using the motion vector f is used as the backward motion vector. A motion vector h to be referred to is used. For example, as a method of using the motion vector f, there is a method of generating a motion vector parallel to the motion vector f. Image data obtained by averaging the forward reference image data and the backward reference image data obtained based on these motion vectors is defined as motion compensated image data.

  In this case, the magnitude of the motion vector g which is the forward motion vector is MVF, the magnitude of the motion vector h which is the backward motion vector is MVB, the magnitude of the motion vector f is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture B7) and the picture (picture P9) referenced by the block of the backward reference picture is TRD, the current picture (picture B6) and the forward reference picture (picture P5). , TRF, and TRB as the temporal distance between the current picture (picture B6) and the backward reference picture (picture B7), the magnitude MVF of the motion vector g and the magnitude MVB of the motion vector h Are obtained by (Equation 3) and (Equation 4), respectively.

  Next, a fourth example when the mode selection is the direct mode will be described with reference to FIG.

  Here, it is assumed that the block a of the picture B6 is decoded, and the block of the picture B7 at the same position as the block a is a block b. It is assumed that the block b is subjected to backward reference prediction encoding as in the third example, and the backward motion vector of the block b is a motion vector f. This motion vector f refers to the picture P9. In this case, the motion vector g referring to the picture P9 obtained using the motion vector f is used as the forward motion vector for the block a, and the picture B7 obtained using the motion vector f is used as the backward motion vector. A motion vector h to be referred to is used. For example, as a method of using the motion vector f, there is a method of generating a motion vector parallel to the motion vector f. Image data obtained by averaging the forward reference image data and the backward reference image data obtained based on these motion vectors is defined as motion compensated image data.

  In this case, the magnitude of the motion vector g which is the forward motion vector is MVF, the magnitude of the motion vector h which is the backward motion vector is MVB, the magnitude of the motion vector f is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture B7) and the picture (picture P9) referenced by the block of the backward reference picture is TRD, the current picture (picture B6), and the backward reference picture (picture B7). ) Is a time distance from a picture (picture P9) referred to by a block, TRF, the magnitude MVF of the motion vector g and the magnitude MVB of the motion vector h are (Equation 1) and (Equation 2), respectively. Is required.

  A fifth example when the mode selection is the direct mode will be described with reference to FIG. Here, it is assumed that the block a of the picture B6 is decoded in the direct mode. In this case, motion compensation is performed by setting the magnitude of the motion vector to 0, performing two-way reference using the picture P5 as the forward reference picture and the picture B7 as the backward reference picture.

  Next, a sixth example when the mode selection is the direct mode will be described with reference to FIG. Here, it is assumed that block a of picture B6 is decoded in the direct mode. In this case, the motion vector g used when decoding the block f in the same position as the block a in the picture P9 which is the P picture behind the picture B6 is used. The motion vector g is stored in the motion vector storage unit 1406. The block a performs bi-directional prediction from the picture P5 that is the forward reference picture and the picture B7 that is the backward reference picture, using the motion vector obtained by using the motion vector g. For example, if a method of generating a motion vector parallel to the motion vector g is used as in the case of the first example, the motion vector used to obtain the motion compensated image data of the block a is It becomes the motion vector i for the motion vector h and the picture B7.

  In this case, the magnitude of the motion vector h that is the forward motion vector is MVF, the magnitude of the motion vector i that is the backward motion vector is MVB, the magnitude of the motion vector g is MV, and the current picture (picture B6) The temporal distance between the P picture (picture P9) located behind and the picture (picture P5) referenced by the block f of the picture located thereafter is TRD, the current picture (picture B6) and the forward reference picture If the temporal distance between (picture P5) is TRF, and the temporal distance between the current picture (picture B6) and the backward reference picture (picture B7) is TRB, the motion vector MVF and the motion vector MVB are ( It is calculated | required by (Formula 1) and (Formula 5).

  Next, a seventh example when the mode selection is the direct mode will be described with reference to FIG. Here, it is assumed that block a of picture B6 is decoded in the direct mode. In this example, the relative index assignment change (remapping) with respect to the picture number described above is performed, and the backward reference picture becomes the picture P9. In this case, the motion vector g used when the block f at the same position as the block a in the picture P9 which is the backward reference picture of the picture B6 is used. The motion vector g is stored in the motion vector storage unit 1406. Block a performs bi-directional prediction from picture P5, which is a forward reference picture, and picture P9, which is a backward reference picture, using a motion vector generated using motion vector g. For example, if a method of generating a motion vector parallel to the motion vector g is used as in the case of the first example, the motion vector used to obtain the motion compensated image data of the block a is It becomes the motion vector i for the motion vector h and the picture P9.

  In this case, the magnitude of the motion vector h that is the forward motion vector is MVF, the magnitude of the motion vector i that is the backward motion vector is MVB, the magnitude of the motion vector g is MV, and the current picture (picture B6) The temporal distance between the backward reference picture (picture P9) and the picture (picture P5) referenced by the block of the backward reference picture is TRD, the current picture (picture B6) and the forward reference picture (picture P5). If the time distance between and is TRF, the magnitude MVF of the motion vector h and the magnitude MVB of the motion vector i are obtained by (Expression 1) and (Expression 2), respectively.

  The motion compensated image data generated in this way is output to the addition operation unit 1408. The addition operation unit 1408 adds the input prediction error image data and motion compensation image data to generate decoded image data. The generated decoded image data is output to the frame memory 1407 via the switch 1410.

  As described above, the processing for one macroblock of the picture B6 is completed. By the same process, the remaining macroblocks are sequentially decoded. When all the macroblocks of the picture B6 are decoded, the picture B8 is decoded.

<Decoding process of picture B8>
Since operations up to the generation of the prediction error image data in the code string analysis unit 1401, the mode decoding unit 1403, and the prediction error decoding unit 1402 are the same as those in the decoding process of the picture P9, description thereof is omitted.

  The motion compensation decoding unit 1405 generates motion compensated image data based on the input motion vector information and the like. The picture B8 is coded with reference to the picture B7 as a forward reference picture and with reference to P9 as a backward reference picture, and these pictures are already decoded and held in the frame memory 1407.

  When the mode selection is bi-prediction inter-picture predictive coding, the motion compensation decoding unit 1405 obtains forward reference image data from the frame memory 1407 based on the forward motion vector information. Further, backward reference image data is acquired from the frame memory 1407 based on the backward motion vector information. Then, the motion compensation decoding unit 1405 generates motion compensation image data by averaging the forward reference image data and the backward reference image data.

  When the mode selection is the direct mode, the motion compensation decoding unit 1405 acquires the motion vector of the picture P9 stored in the motion vector storage unit 1406. The motion compensation decoding unit 1405 acquires the forward reference image data and the backward reference image data from the frame memory 1407 using the motion vector. Then, the motion compensation decoding unit 1405 generates motion compensation image data by averaging the forward reference image data and the backward reference image data.

  An example in which the mode selection is the direct mode will be described with reference to FIG. Here, it is assumed that the block a of the picture B8 is decoded, and the block b is located at the same position as the block a in the picture P9 which is the backward reference picture. Then, the forward motion vector of the block b is set as a motion vector c. This motion vector c refers to the picture P5. In this case, the motion vector d referring to the picture B7 generated using the motion vector c is used as the forward motion vector for the block a, and the picture P9 generated using the motion vector c is used as the backward motion vector. A reference motion vector e is used. For example, as a method of using the motion vector c, there is a method of generating a motion vector parallel to the motion vector c. Image data obtained by averaging the forward reference image data and the backward reference image data obtained based on these motion vectors is defined as motion compensated image data.

  In this case, the magnitude of the motion vector d that is the forward motion vector is MVF, the magnitude of the motion vector e that is the backward motion vector is MVB, the magnitude of the motion vector c is MV, and the current picture (picture B8) The temporal distance between the backward reference picture (picture P9) and the picture (picture P5) referenced by the block b of the backward reference picture is TRD, the current picture (picture B8) and the forward reference picture (picture B7). ) And TB, and the temporal distance between the current picture (picture B8) and the backward reference picture (picture P9) is TRB, the magnitude MVF of the motion vector d and the magnitude MVB of the motion vector e Are obtained by (Equation 1) and (Equation 5), respectively.

  The motion compensated image data generated in this way is output to the addition operation unit 1408. The addition operation unit 1408 adds the input prediction error image data and motion compensation image data to generate decoded image data. The generated decoded image data is output to the frame memory 1407 via the switch 1410.

  As described above, the processing of one macroblock of picture B8 is completed. By the same process, the remaining macroblocks are sequentially decoded. Hereinafter, each picture is decoded by the same processing according to the picture type.

  Next, the frame memory control unit 1404 rearranges the image data of each picture held in the frame memory 1407 as described above in order of time as shown in FIG.

  As described above, in the moving picture decoding method according to the present invention, when decoding a B picture that has been subjected to inter-picture prediction encoding processing using bi-directional prediction, as a forward reference and a backward reference, As a picture to be used, decoding is performed using pictures that are already decoded and are located in the vicinity in the order of display time.

  Also, when the direct mode is selected as the encoding mode for the B picture, the decoding is already performed by referring to the motion vector of the backward reference picture that has already been decoded and is stored in the motion vector storage unit 1406. Reference image data is acquired from the converted image data, and motion compensated image data is obtained.

  As a result of such operations, when coding a B picture for which inter-picture predictive coding processing is performed using bi-directional prediction, pictures that are located in the order of display time are used as pictures used as forward reference and backward reference. It is possible to correctly perform a decoding process when decoding a code string generated by encoding using the code string.

  In this embodiment, seven examples have been described in the direct mode. For example, this is uniquely determined for each macroblock or block by a decoding method of the block at the same position of the backward reference picture. One determined method may be used, or a plurality of methods may be switched and used in units of blocks or macroblocks. When a plurality of methods are used, decoding is performed using information indicating which direct mode is used described in the code string. At this time, the operation of the motion compensation decoding unit 1405 varies depending on the information. For example, when this information is added in units of motion compensation blocks, the mode decoding unit 1403 determines which direct mode is used for encoding, and notifies the motion compensation decoding unit 1405 of it. Then, the motion compensation decoding unit 1405 performs a decoding process using the decoding method described in this embodiment depending on which direct mode is used.

  In this embodiment, the case of a picture configuration in which three B pictures are sandwiched between I or P pictures has been described. However, the number of B pictures may be a different value, for example, four or five. There may be.

  In the present embodiment, the P picture is encoded with reference to one encoded I or P picture positioned forward or backward in the display time order, and the B picture is forward or backward in the display time order. In the case of decoding a code string that has been encoded with reference to two encoded pictures in the vicinity of the position, these are positioned forward or backward in the order of display time in the case of a P picture. A plurality of encoded I or P pictures are used as reference picture candidates, and each block is encoded with reference to at most one picture. In the case of a B picture, it is positioned forward or backward in display time order. A plurality of encoded pictures in the vicinity may be used as reference picture candidates, and a code string may be encoded with reference to a maximum of two pictures in each block.

  In addition, when storing the motion vector in the motion vector storage unit 1406, the motion compensation decoding unit 1405, when the target block is encoded by bi-directional prediction or direct mode, both forward and backward directions. A motion vector may be stored, or only a forward motion vector may be stored. If only the forward motion vector is stored, the memory amount of the motion vector storage unit 1406 can be reduced.

(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. 15 is an explanatory diagram in the case of implementing by a computer system using a flexible disk storing the moving picture coding method or the moving picture decoding method of each of the above embodiments.

  FIG. 15B shows an appearance, a cross-sectional structure, and a flexible disk as viewed from the front of the flexible disk, and FIG. 15A 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. 15C shows a configuration for recording and reproducing the program on the flexible disk FD. When the program is recorded 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. 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 moving picture coding method and the moving picture decoding method shown in the above embodiment and a system using the same will be described.

  FIG. 16 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. 16, 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. 17 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 mobile 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 outputting audio, and a voice 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 the recording medium ex207 to be attached to the mobile phone ex115 The it 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 in ex306, a digital analog conversion process and a frequency conversion process are performed in the transmission / reception circuit unit ex301, and then the signal is 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, whereby, for example, moving image data included in the moving image file linked to the home page is displayed. 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

  Note that the present invention is not limited to the above system, and recently, satellite and terrestrial digital broadcasting has become a hot topic. As shown in FIG. 19, the digital broadcasting system also includes at least the moving image encoding apparatus of the above embodiment or 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. 18, 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 mounting 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.

  As described above, the moving image encoding method and the moving image decoding method according to the present invention generate a code string by encoding a moving image by using, for example, a mobile phone, a DVD device, and a personal computer. This is useful as a method for decoding a coded sequence.

It is a block diagram which shows the structure of one Embodiment of the moving image encoding apparatus using the moving image encoding method which concerns on this invention. It is explanatory drawing of the picture number and relative index in embodiment of this invention. It is a conceptual diagram of the image coding signal format by the moving image coding apparatus in embodiment of this invention. It is a schematic diagram which shows the order of the picture in the memory for rearrangement of embodiment of this invention, (a) The input order, (b) It is a figure which shows the rearranged order. It is a schematic diagram which shows the motion vector in direct mode in embodiment of this invention, (a) When the object block is picture B7, (b) The 1st and 2nd when object block a is picture B6 (C) A third example when the target block a is a picture B6, and (d) a fourth example when the target block a is a picture B6. It is a schematic diagram which shows the motion vector in direct mode in embodiment of this invention, (a) The 5th example in case the object block a is the picture B6, (b) When the object block a is the picture B6 (C) A seventh example when the target block a is a picture B6, and (d) a case where the target block a is a picture B8. It is the schematic diagram which shows the prediction relationship and order of the picture in embodiment of this invention, (a) Prediction relationship of each picture shown by display time order, (b) It rearranged in encoding order (code sequence order) It is a figure which shows a picture order. It is the schematic diagram which shows the prediction relationship and order of the picture in embodiment of this invention, (a) Prediction relationship of each picture shown by display time order, (b) It rearranged in encoding order (code sequence order) It is a figure which shows a picture order. It is a schematic diagram showing the prediction relationship and order of pictures in the embodiment of the present invention, (a) prediction relationship of each picture shown in display time order, (b) rearranged in coding order (code string order) It is a figure which shows a picture order. FIG. 5 is a schematic diagram hierarchically showing a picture prediction structure shown in FIG. 4 according to the embodiment of the present invention. FIG. 8 is a schematic diagram hierarchically showing the picture prediction structure shown in FIG. 7 according to the embodiment of the present invention. FIG. 9 is a schematic diagram hierarchically showing a picture prediction structure shown in FIG. 8 according to the embodiment of the present invention. FIG. 10 is a schematic diagram hierarchically showing a picture prediction structure shown in FIG. 9 according to the embodiment of the present invention. It is a block diagram which shows the structure of one Embodiment of the moving image decoding apparatus using the moving image decoding method which concerns on this invention. 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 Embodiment 1 by a computer system, (a) Of the flexible disk which is a recording medium main body An explanatory diagram showing an example of a physical format, (b) an external view seen from the front of the flexible disk, a cross-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 the content supply system which implement | achieves a content delivery service. It is the schematic which shows an example of a mobile telephone. It is a block diagram which shows the internal structure of a mobile telephone. It is a block diagram which shows the whole structure of the system for digital broadcasting. It is a schematic diagram which shows the prediction relationship and order of the picture in the conventional moving image encoding method, (a) It shows the relationship between each picture and the corresponding reference picture, (b) Shows the order of the code string produced | generated by encoding FIG. It is a schematic diagram which shows the motion vector in the direct mode in the conventional moving image encoding method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Memory for rearrangement 102 Difference calculation part 103 Prediction error encoding part 104 Code sequence generation part 105 Prediction error decoding part 106 Addition calculation part 107 Reference picture memory 108 Motion vector detection part 109 Mode selection part 110 Encoding control part 116 Motion vector storage unit 1401 Code sequence analysis unit 1402 Prediction error decoding unit 1403 Mode decoding unit 1404 Frame memory control unit 1405 Motion compensation decoding unit 1406 Motion vector storage unit 1407 Frame memory 1408 Addition operation unit

Claims (6)

A moving image decoding method for decoding a code string generated by encoding image data corresponding to each picture constituting a moving image,
When decoding the block to be decoded,
A motion vector of the decoding target block is determined based on a motion vector of a block in the picture that has already been decoded and that is also a block in the same position as the decoding target block. ,
Using a motion vector of the decoding target block and a reference picture corresponding to the motion vector of the decoding target block, and a decoding step of decoding by performing motion compensation on the decoding target block in direct mode. A video decoding method as a feature. In the decoding step,
When the same position block is decoded using one motion vector and one backward reference picture corresponding to the one motion vector,
The single motion vector used for decoding the same position block is scaled using a difference in information indicating the display order of pictures, thereby performing motion compensation on the decoding target block in the direct mode. Generating two motion vectors for the decoding target block,
Using the generated two motion vectors and the two reference pictures corresponding to the generated two motion vectors, respectively, to perform decoding by performing motion compensation on the decoding target block in the direct mode. The moving image decoding method according to claim 1. Among the two reference pictures respectively corresponding to the two motion vectors of the decoding target block,
A first reference picture is a picture including the same position block;
The second reference picture is one backward reference picture used when decoding the same position block, and the motion subjected to scaling when generating two motion vectors of the decoding target block The moving picture decoding method according to claim 2, wherein the reference picture corresponds to a vector. The information indicating the display order of pictures includes first information indicating a display order of pictures including the decoding target block, second information indicating a display order of the second reference picture of the decoding target block, and , Third information indicating a display order of pictures that are also pictures including the same position block and also the first reference picture of the decoding target block;
The difference in information is a difference between first information and second information, a difference between first information and third information, and a difference between second information and third information. Video decoding method. A moving image decoding apparatus for decoding a code string generated by encoding image data corresponding to each picture constituting a moving image,
When decoding the block to be decoded,
A motion vector of the block to be decoded is determined based on a motion vector of a block in a picture that has already been decoded and that is also in the same position as the block to be decoded. ,
Using a motion vector of the block to be decoded and a reference picture corresponding to the motion vector of the block to be decoded, and comprising decoding means for decoding the block to be decoded with motion compensation in a direct mode,
In the decoding means,
When the same position block is decoded using one motion vector and one backward reference picture corresponding to the one motion vector,
The single motion vector used for decoding the same position block is scaled using a difference in information indicating the display order of pictures, thereby performing motion compensation on the decoding target block in the direct mode. Generating two motion vectors for the decoding target block,
Using the generated two motion vectors and the two reference pictures corresponding to the generated two motion vectors, respectively, to perform decoding by performing motion compensation on the decoding target block in the direct mode. Video decoding device. A data storage medium storing a program for performing a decoding process for decoding a code string corresponding to a moving image,
A data storage medium, wherein the program causes a computer to perform the decoding process by the moving image decoding method according to claim 1.

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