JP2004048711A - Method for coding and decoding moving picture and data recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable use of B picture and directional modes even if a picture coded behind in a displaying order cannot be referred to, and maintain high coding efficiency. <P>SOLUTION: In the circumstance where the picture coded behind in the displaying order sequentially cannot be referred to, motion vectors in already-coded blocks in the same picture are referred to when performing predictive coding using the directional mode. A method thus realizes the directional mode without referring to the following picture in the sequential order. Furthermore, by deleting an item of referencing rearward picture reference from a table of the coding modes, thereby reducing the number of the items in the table, the high coding efficiency is also achieved in a motion compensation only to the forward direction. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a moving picture coding method and a moving picture decoding method, and in particular, to a prediction code for a B picture that performs prediction coding with reference to a plurality of previously coded pictures that are temporally forward or backward. And a prediction decoding method.
[0002]
[Prior art]
Generally, in coding of a moving image, the amount of information is compressed by reducing redundancy in the time direction and the space direction. Therefore, in inter-picture predictive coding for the purpose of reducing temporal redundancy, motion detection and motion compensation are performed in block units with reference to a forward or backward picture, and the obtained predicted image is compared with the current picture. Is performed on the difference value of.
[0003]
H.264, which is a moving picture coding method currently being standardized, In 26L, a picture (I picture) for which only intra-picture prediction coding is performed, a picture (P picture) for which inter-picture prediction coding is performed with reference to one picture that is temporally forward, and A picture (B picture) for performing inter-picture predictive encoding with reference to two pictures in the front, two pictures in the back in time, or one picture in the front and the back in time is referred to. Proposed. H. In MPEG (Motion Picture Experts Group) 1, MPEG2, and MPEG4, which are encoding methods before 26L, a B picture can refer to only one picture in the same direction. One major feature of the 26L is that it has been changed so that two sheets can be referenced.
[0004]
FIG. 16 is a diagram illustrating an example of a reference relationship between each picture and a picture referred to by the picture in the conventional moving picture coding method. In the figure, picture I1 to picture B20 are displayed in this order. FIG. 17 (a) is a diagram showing the pictures around the picture B18 shown in FIG. 16 extracted in the display order. FIG. 17B is a diagram illustrating the encoding order of the peripheral pictures of the picture B18 when the picture B18 is encoded with the reference relationship illustrated in FIG. 17A.
[0005]
The picture I1 does not have a reference picture and performs intra-picture predictive coding, and the picture P10 performs inter-picture predictive coding with reference to a temporally preceding picture P7. Picture B6 refers to two temporally forward pictures (picture I1 and picture P4), picture B12 refers to two temporally backward pictures (picture P13 and picture P16), and picture B18. Performs inter-picture predictive coding with reference to one picture (picture P16 and picture P19) that is temporally forward and backward. As described above, in the encoding using the B picture, the picture located later in time is referred to, so that the encoding cannot be performed in the display order. That is, when there is a B picture such as the picture B18 in FIG. 17A, it is necessary to encode the picture P19 referred to by the B picture first. Therefore, the picture B16 to the picture B19 must be rearranged in the order shown in FIG.
[0006]
There is a skip mode as one of the prediction modes of a P picture in which inter-picture prediction coding is performed with reference to one temporally forward picture. In the skip mode, the encoding target block does not have the motion vector information directly, and determines the motion vector to be used for the motion compensation of the encoding target block by referring to the motion vector of the encoded block located in the vicinity. Motion compensation is performed by generating a prediction image from a P picture temporally immediately before the picture to which the coding target block belongs.
[0007]
FIG. 18 is a diagram illustrating a positional relationship between a coded block whose motion vector is referred to and a current block when referring to a motion vector of a coded block located around the current block in the same picture. is there. FIG. 18A shows an example in which the encoding target block BL51 to be encoded has a size of 16 pixels × 16 pixels, and FIG. 18B shows an example in which the encoding block BL52 is 8 pixels × 8 pixels. The example in the case of the size is shown. Here, the positional relationship between a coded block whose motion vector is referred to in the P picture skip mode and the current block to be coded is shown. The block BL51 is a block of 16 pixels × 16 pixels for which coding is performed using the skip mode, and basically includes three coded blocks having a positional relationship of A, B, and C (hereinafter, blocks located at the position of A). Are referred to as blocks B and C at the positions of blocks A and B, respectively, and the block at the position of C is referred to as block C.). However, if the following condition is satisfied, the motion vector is not referred to, the value of the motion vector of the current block is set to “0”, and the immediately preceding P picture is referred to perform motion compensation in the direct mode.
[0008]
1. When the block A or the block B is outside the picture or the slice to which the encoding target block belongs.
2. When the block A or the block B has a motion vector of a value “0” referring to the immediately preceding picture.
[0009]
Only the motion vector that refers to the immediately preceding P picture is extracted from the motion vectors of the three blocks A, B, and C that have been referred to, and the median value is used to actually use it in the direct mode. Let it be a motion vector. However, when the block C cannot be referred to, the motion vector of the block D is used instead.
[0010]
FIG. 19 is a diagram illustrating an example of a motion vector referred to in the skip mode of a P picture and an encoded picture referred to by the motion vector. It is assumed that a block BL51 belonging to the picture P64 is a currently coded block. In this example, the motion vector referring to the immediately preceding picture is only the motion vector MVA1, and the motion vector MV1 used in the direct mode uses the value of the motion vector MVA1 as it is. By using such a reference method, it is not necessary to encode a motion vector, so that the bit amount of an output code string can be reduced. Further, since the motion vector is determined with reference to the surrounding blocks, the effect is greatly obtained when the imaged object moves in a certain direction due to the influence of the camera pan or the like.
[0011]
B picture for which inter-picture predictive coding is performed with reference to two temporally forward pictures or two temporally backward pictures or one temporally forward and backward picture. There is a direct mode as one of the prediction modes. In the direct mode, the block to be coded does not have a direct motion vector, but refers to the motion vector of the block at the same position in the coded picture that is temporally immediately after the picture to be coded. Two motion vectors for actually performing motion compensation of the current block are calculated, and a predicted image is created.
[0012]
FIG. 20 is a diagram for explaining a method of determining a motion vector in the direct mode. The picture B73 is a current B picture to be coded, and performs bidirectional prediction in the direct mode using the picture P72 and the picture P74 as reference pictures. Assuming that a block to be coded is a block BL71, two motion vectors required at this time are determined using a motion vector MV71 of a block BL72 at the same position of a picture P74 which is a coded backward reference picture. Is done. The two motion vectors MV72 and MV73 used in the direct mode are calculated by applying scaling to the motion vector MV71 using the picture intervals TR72 and TR73 or by applying a predetermined coefficient to the motion vector MV71. Is done. By averaging the pixel values of the two reference images specified by the two motion vectors, a predicted image required for encoding the block BL71 is generated. As described above, in a block that performs encoding in the direct mode, it is not necessary to encode a motion vector, so that the bit amount of an output code string can be reduced.
[0013]
[Non-patent document 1]
J. Joint Video Team (JVT) of ISO / IEC MPEG and ITU-T VCEG --- JointCommittee Draft (2002-5-10) 99 11 B pictures
[0014]
[Problems to be solved by the invention]
However, in the encoding of a moving image using the direct mode of a B picture, encoding is performed with reference to a picture that is temporally backward, so that the picture that may be referred to is a picture to be encoded. It had to be encoded before. For this reason, in an environment where it is not possible to first encode and decode a picture that is later in time, encoding using the direct mode of the B picture cannot be performed.
[0015]
The present invention is to solve the above problems, even in an environment in which a picture that is temporally backward is not coded and decoded earlier than the current picture or the current picture to be decoded, It is a first object of the present invention to propose a method that enables B-pictures, particularly direct mode, to be used without contradiction. Further, the present invention proposes a highly efficient moving picture encoding method and a decoding method using a B picture by proposing an efficient reference method of a table that associates an encoding mode with its identification number. This is a second object.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, a moving image encoding method according to the present invention is a moving image encoding method that encodes a moving image to generate a code sequence. In the coding of a B picture that performs predictive coding with reference to a plurality of pictures, it is possible to use the direct mode of performing motion compensation of a current block with reference to a motion vector of a coded block. When performing the predictive encoding of the B picture by referring to only the encoded picture in one direction in display order from the picture to which the encoding target block belongs, A motion compensation step of performing motion compensation by referring to a motion vector of an encoded block in the same picture located around the current block as the direct mode. And wherein the Mukoto.
[0017]
Further, the moving picture coding method of the present invention is a moving picture coding method for coding a moving picture to generate a code string, and refers to a plurality of coded pictures that are temporally forward or backward. In the encoding of a B picture to be subjected to predictive encoding, an encoding step that enables to use a direct mode for performing motion compensation of a current block with reference to a motion vector of an encoded block, The encoding step includes performing the predictive encoding of the B picture by referring to only the encoded picture in one direction in display order from the picture to which the encoding target block belongs, and performing the encoding as the direct mode. It is characterized in that the motion compensation is performed by referring to one or a plurality of pictures in order from the temporally closest one with the value of the motion vector of the target block being “0”.
[0018]
Further, in the moving picture coding method according to the present invention, the coding step refers to the backward from a table in which the predictive coding method of the B picture is associated with an identifier for identifying the predictive coding method. Excluding the predictive encoding method, the method includes a table regenerating step of regenerating the table. In the encoding step, the identifier indicating the predictive encoding method of the B picture is encoded using the regenerated table. May be changed.
[0019]
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 sequence obtained by coding a moving picture. When decoding a B picture that performs predictive decoding with reference to a plurality of decoded pictures, use a direct mode that performs motion compensation on the current block with reference to a motion vector of the decoded block. And decoding the B picture by predicting only the decoded picture in one direction in time from the picture to which the current block belongs. When performing the motion compensation, the direct mode refers to a motion vector of a decoded block in the same picture positioned around the current block and performs motion compensation. Characterized in that it comprises a step.
[0020]
Further, the moving picture decoding method of the present invention is a moving picture decoding method for decoding a code sequence obtained by coding a moving picture, wherein a plurality of decoded pictures which are temporally forward or backward are decoded. In the decoding of a B picture that performs predictive decoding with reference to the above, it is possible to use the direct mode of performing motion compensation on the current block with reference to the motion vector of the decoded block. The predicting decoding of the B picture by referring to only the decoded picture in one direction in time from the picture to which the decoding target block belongs. And performing motion compensation by referring to one or a plurality of pictures in order from the temporally closest one, with the value of the motion vector of the decoding target block being “0”. That.
[0021]
Further, in the moving picture decoding method according to the present invention, the decoding step includes the step of storing a previously stored table in which the predictive decoding method of the B picture is associated with an identifier for identifying the predictive decoding method. Excluding a predictive decoding method that refers to backward from inside, the method includes a table regenerating step of regenerating the table. In the decoding step, a predictive decoding method for the B picture is identified from the coded sequence. May be decoded, the prediction decoding method of the B picture is identified using the regenerated table, and the prediction decoding of the current block is performed according to the identified prediction decoding method.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of a moving image encoding device 100 that executes the moving image encoding method according to the first embodiment. When encoding a B picture in the direct mode, the moving picture encoding apparatus 100 refers to only a picture that is ahead of the current picture in display order and is located around the current block in the same picture. A moving picture coding apparatus that determines a motion vector of a current block by referring to a motion vector of a coded block, comprising: a frame memory 101; a prediction residual coding unit 102; a code sequence generation unit 103; It includes a difference decoding unit 104, a frame memory 105, a motion vector detection unit 106, a mode selection unit 107, a motion vector storage unit 108, a backward picture determination unit 109, a difference calculation unit 110, an addition calculation unit 111, a switch 112, and a switch 113. .
[0023]
The frame memory 101, the frame memory 105, and the motion vector storage unit 108 are memories realized by a RAM or the like. The frame memory 101 is for rearranging each picture of a moving image input in display order in encoding order. Provide storage area.
[0024]
The prediction residual encoding unit 102 performs frequency conversion such as DCT on the prediction residual obtained by the difference calculation unit 110, quantizes and outputs the result. The code sequence generation unit 103 performs variable length coding on the coding result from the prediction residual coding unit 102, converts the coding result into a format of a coded sequence for output, and describes information related to the prediction coding method. A code string is generated with additional information such as a header. The prediction residual decoding unit 104 performs variable-length decoding on the encoding result from the prediction residual encoding unit 102, performs inverse quantization, and performs inverse frequency transform such as IDCT transform to generate a decoded prediction residual. I do.
[0025]
The frame memory 105 provides a storage area for holding a predicted picture in a picture unit. The motion vector detection unit 106 detects a motion vector for each predetermined unit such as a macroblock or a block obtained by further dividing the macroblock. The mode selection unit 107 selects an optimal prediction mode while referring to the motion vector used for the coded picture stored in the motion vector storage unit 108 and indicates the best prediction mode by using the motion vector detected by the motion vector detection unit 106. Each block in the predicted picture to be read is read from the frame memory 105 and output to the difference calculation unit 110.
[0026]
The motion vector storage unit 108 provides a storage area for holding a motion vector detected for each block of an encoded picture. The backward picture determination unit 109 determines whether or not a picture behind the current picture in display order has already been coded. The difference calculation unit 110 outputs a difference between a coding-target macroblock and a macroblock of a predicted image determined by a motion vector.
[0027]
The addition operation unit 111 adds the decoded prediction residual output from the prediction residual decoding unit 104 and the block of the predicted picture output from the mode selection unit 107 to obtain an addition result (a prediction picture is formed). Block) is stored in the frame memory 105. The switch 112 is switched in accordance with the picture type of the picture to be coded, and makes the readout line of the frame memory 101 and the prediction residual coding unit 102 conductive for an I picture to be subjected to intra prediction coding. As a result, each macroblock of the current picture read from the frame memory 101 is directly input to the prediction residual encoding unit 102.
[0028]
In the case of a P picture and a B picture for which inter-picture prediction coding is performed, the output side of the difference calculation unit 110 and the prediction residual coding unit 102 are made conductive. As a result, the calculation result of the difference calculation unit 110 is input to the prediction residual coding unit 102. The switch 113 is switched between conduction and blocking according to the picture type of the current picture. The output side of the mode selection unit 107 and the input side of the addition operation unit 111 are shut off for an I picture for which intra prediction coding is performed, and for a P picture and a B picture for which inter prediction coding is performed, the mode selection unit 107 The output side and the input side of the addition operation unit 111 are conducted. As a result, in an I picture for which intra prediction coding is performed, the decoded prediction residual decoded by the prediction residual decoding unit 104 is output to the frame memory 105.
[0029]
Hereinafter, the moving picture coding method according to the first embodiment of the present invention will be described with reference to the block diagram shown in FIG.
A moving image to be encoded is input to the frame memory 101 in picture order in time order. Each picture is divided into blocks called, for example, 16 pixels in the horizontal direction and 16 pixels in the vertical direction, which are called macroblocks, and the subsequent processing is performed in block units.
[0030]
The macroblock read from the frame memory 101 is input to the motion vector detection unit 106. The motion vector detection unit 106 detects a motion vector of a macroblock to be coded using an image stored in the frame memory 105 (an image obtained by further decoding a coded picture) as a reference picture. I do. In the prediction mode other than the direct mode, the motion vector detection unit 106 determines the size of each macroblock or an area obtained by dividing the macroblock (for example, a size such as 16 pixels × 8 pixels, 8 pixels × 16 pixels, and 8 pixels × 8 pixels). A motion vector is detected for each of the divided small blocks.
[0031]
The motion vector detection unit 106 predicts that a previously coded picture is used as a reference picture for a macroblock to be coded, and predicts that the pixel value of the current block is closest to the configuration of the pixel value of the current block in a search area within the picture. A motion vector indicating the position of the block to be processed is detected. The mode selection unit 107 selects an optimal prediction mode while referring to the motion vector stored in the motion vector storage unit 108 and used for the coded picture. At this time, the backward picture determination unit 109 determines whether or not the picture behind in the display order has already been encoded. If it is determined that the backward picture is not coded, the mode selection unit 107 selects a prediction mode that does not refer to the backward picture in the display order in the encoding of the B picture.
[0032]
According to the prediction mode selected by the mode selection unit 107, the optimal motion vector is determined from the motion vectors detected by the motion vector detection unit 106, and the prediction block referred to by the determined motion vector is read from the frame memory 105. It is output and input to the difference calculation unit 110. The difference calculation unit 110 generates a prediction residual image by calculating the difference between the prediction block and the macroblock to be encoded. The generated prediction residual image is input to the prediction residual encoding unit 102, and is subjected to frequency conversion and quantization in the prediction residual encoding unit 102. The above processing flow is the operation when the inter-picture prediction coding is selected. However, the switch 112 switches to the intra-picture prediction coding. Finally, the code sequence generation unit 103 performs variable length coding on control information such as a motion vector and image information output from the prediction residual coding unit 102, and generates a finally output code sequence. Is done.
[0033]
The outline of the flow of the encoding has been described above. Hereinafter, the details of the processing in the direct mode in the mode selection unit 107 will be described. Here, a case will be described in which the rear picture determination unit 109 determines that the rear picture is not coded. FIG. 2 is a diagram illustrating an example of a reference relationship between the pictures in a case where it is not possible to refer to a picture in the display order behind a picture to which the coding target block belongs. As shown in the figure, all the B pictures included in the display order sequence of the pictures are subjected to predictive encoding with reference to one or a plurality of encoded pictures located ahead in the display order. For example, the picture B82 and the picture B83, both of which are B pictures, have only the coded picture P81 ahead in the display order, so that the motion compensation is performed with reference to only the picture P81.
[0034]
Further, as for picture B85 and picture B86, both of which are B pictures, picture B85 refers to two coded pictures (picture P81 and picture P84) located in the front in display order. The motion compensation is performed by referring only to the picture P84 that is temporally closer in the display order without referring to the picture P81 that is temporally farther in the display order. In such a case, the motion vectors of each B picture all refer to encoded pictures that are ahead of the current picture in display order.
[0035]
In the present embodiment, when the direct mode is selected by the mode selection unit 107 when predictive encoding of a B picture is performed in an environment in which a picture backward in the display order is not encoded, as in the related art, Instead of generating the motion vector of the current block by referring to the motion vector of the coded block belonging to the picture immediately following the current picture in display order (hereinafter referred to as “temporal prediction”), A direct mode is realized by generating a motion vector of the current block with reference to a motion vector of a coded block located around the current block (hereinafter referred to as “spatial prediction”).
[0036]
FIG. 3 is a flowchart illustrating an example of the operation of the mode selection unit 107 when the direct mode is selected. When the direct mode is selected, the mode selection unit 107 first causes the backward picture determination unit 109 to determine whether or not a picture behind the current picture in display order has been coded (S501). If the result of the determination is that the picture behind in the display order has already been coded, predictive coding of the current block is performed using temporal prediction as in the prior art (S502). Then, the mode selection unit 107 ends the processing of the current block, and moves on to the processing of the next current block.
[0037]
Also, as a result of the determination in step S501, if the picture in the rear in the display order is not coded, predictive coding of the coding target block is performed using the above spatial prediction (S503). Further, the mode selection unit 107 sets the value of the flag spatial_flag indicating that the spatial prediction has been performed to “1” and outputs the value to the code sequence generation unit 103 (S504). After that, the mode selection unit 107 ends the processing of the current block to be processed, and proceeds to the processing of the next current block.
[0038]
Hereinafter, a specific method of the spatial prediction performed in step S503 of FIG. 3 will be described.
The example of the skip mode described with reference to FIG. 19 is for the case where the encoded block to be referred to has one motion vector at a time. However, among the prediction modes of the B picture, as shown in FIG. 2, there is also a mode in which the motion compensation is performed by simultaneously referring to two pictures ahead in the display order. In such a mode, one block has two motion vectors. FIG. 4 is a diagram illustrating an example of a motion vector reference relationship in a case where a block having two motion vectors is included in an encoded block whose motion vector is referred to. The picture P94 is a picture currently being coded, and the block BL51 is a block for performing predictive coding in the direct mode.
[0039]
First, as a first method, the mode selection unit 107 sets the block BL51 (or the block BL52) in any case where the block BL51 for performing predictive encoding in the direct mode is the one shown in FIGS. 18A and 18B. ) Basically refers to the motion vector of the block at the position of A, B, C. However, the reference is changed according to the following conditions.
[0040]
1. If the block C cannot be referred to, the block at the positions A, B, and D is referred to.
If there is a block that cannot refer to a motion vector among the three blocks located at 2, A, B, and C, or A, B, and D, the block is excluded from motion vector reference targets.
[0041]
The mode selection unit 107 determines, among the motion vectors of the three blocks A, B, and C (or A, B, and D) that have been referred to, the picture referenced by the motion vector and the picture to be coded. Compare the perspective in the display order of. From the comparison, a motion vector that refers to a picture located closest to the current picture in display order is extracted. When there are a plurality of extracted motion vectors, the median value or the average value thereof is taken. For example, a median value may be taken when there are an odd number of extracted motion vectors, and an average value may be taken when there are even numbered motion vectors. The motion vector obtained in this way is used as the motion vector of the current block when the direct mode is selected, when the motion compensation is performed with reference to only the picture preceding the current picture in the display order. . When all the blocks A, B, and C (or A, B, and D) cannot be referred to, the motion vector of the current block is set to 0, and the picture to be referred to is set as the immediately preceding picture. I do.
[0042]
FIG. 5 is a flowchart illustrating an example of a processing procedure when the mode selection unit 107 illustrated in FIG. 1 performs spatial prediction of the current block using the first method. Hereinafter, the encoding target block BL51 illustrated in FIG. 4 will be described as an example. First, the mode selection unit 107 checks whether or not the block at the position C with respect to the encoding target block BL51 can be referred to (S601). In FIG. 4, the block at the position C has a motion vector MVC1 referring to the picture P93 and a motion vector MVC2 referring to the picture P92. Therefore, the mode selection unit 107 refers to the motion vectors of the blocks at the positions of A, B, and C (S602).
[0043]
The block at the position A has a motion vector MVA1 referring to the picture P93, and the block at the position B has a motion vector MVB1 referring to the picture P93 and a motion vector MVB3 referring to the picture P91. In step S601, the block at the position C is outside the current picture P94, outside the slice to which the current block BL51 belongs, or because encoding such as intra prediction has been performed. If there is no motion vector, the motion vector of the block at the position D shown in FIGS. 18A and 18B is referred to instead of the block at the position C (S603). That is, three blocks at positions A, B, and D are referred to.
[0044]
Next, the mode selection unit 107 selects a slice that is outside the current picture P94 or belongs to the current block BL51 among the three referenced blocks (A, B, C or A, B, D). , Or does not have a motion vector due to encoding such as intra prediction, the block is excluded from reference candidates, and the motion vector of the encoding target block is calculated ( S604).
[0045]
In addition, when all blocks cannot be referred to among the three blocks (A, B, C or A, B, D), the motion vector of the current block is set to “0”, and the motion vector immediately before the current picture to be coded is set. Refers to a picture. When the mode selection unit 107 extracts only one of the referenced motion vectors that refers to the picture closest to the current picture in display order, the motion vector MVA1, the motion vector MVB1, and the motion vector MVA1 referencing the picture P93. The motion vector MVC1 is obtained. The mode selection unit 107 further takes the median value or the average value. For example, in this case, since three motion vectors are obtained, a median value is obtained. Thereby, one motion vector MV1 for performing motion compensation of the block BL51 can be determined.
[0046]
FIG. 6 is a diagram illustrating an example of a data structure for each slice of the code string generated by the code string generation unit 103 illustrated in FIG. The code string of each picture is composed of a plurality of slice data, and each slice data is composed of a plurality of macroblock data. As shown in the figure, a slice header is added to each slice data in the code string, and information about the slice and the like is written in the slice header. The information on the slice describes, for example, the number of the frame to which the slice belongs, a flag spatial_flag indicating the type of the encoding method in the direct mode, and the like.
[0047]
As described above, in the above embodiment, even in an environment where it is not possible to refer to a picture located backward in the display order, it is possible to directly refer to a picture located backward in the display order when performing predictive encoding using the direct mode. A method for realizing the mode was proposed, and a coding method for realizing high coding efficiency was shown.
[0048]
Note that, in the first method, among the referenced motion vectors, the one that refers to the picture closest to the encoding target picture in display order is extracted. Only the picture that refers to the immediately preceding picture may be extracted. In the case of the example shown in FIG. 4, among the pictures referenced by the referenced motion vector, the picture closest to the current picture in display order is the picture immediately before the current picture. The vectors are the same. If there is no motion vector that refers to the closest picture in the display order, the encoding in the direct mode is performed with the motion vector of the encoding target block set to “0”.
[0049]
Further, in the first method, when determining a motion vector to be used in the direct mode, by referring to a picture located in the foreground from a picture to be coded in display order from among pictures referred to by neighboring coded blocks. Only one motion vector is taken out and one motion vector is finally calculated. Instead, as a second method, a motion vector referring to N pictures from the front of the current picture in the display order is calculated. One motion vector is determined for each picture taken out and referred to, and the obtained N motion vectors are subjected to motion compensation for referencing only the forward direction as motion vectors used for predictive coding in the direct mode. It is also possible. At this time, the predicted image is generated by calculating the average of the pixel values of N regions specified by the N motion vectors.
[0050]
Note that it is also possible to generate a predicted image by a method of averaging by weighting the pixel values of each area instead of a simple average. By using this method, it is possible to realize more accurate motion compensation for an image sequence in which pixel values gradually change in display order.
[0051]
FIG. 7 is a diagram illustrating an example of a motion vector referencing method in a case where two motion vectors are calculated by extracting a motion vector referring to two pictures in front of the current picture in display order and calculating two motion vectors. Picture P104 is a picture currently being coded, and BL51 is a block for performing predictive coding in the direct mode. Using the motion vector MVA1, the motion vector MVB1, and the motion vector MVC1 that refer to the picture P103 that is the closest in the display order among the pictures referred to by the plurality of motion vectors to be referred, The motion vector MV1 is determined by taking the average value, and the median value or average value of the motion vector referring to the picture P102 which is two before in the display order, that is, the motion vector MV2 is determined by taking MVC2 itself. The coding in the direct mode is performed using these two motion vectors.
[0052]
It should be noted that instead of using only the one that refers to one or N pictures from the front in the display order from among the motion vectors of the blocks referred to in FIGS. 18A and 18B, It is also possible to take out only the motion vector referring to the specified picture, determine the value of the motion vector of the current block to be used in the direct mode, and perform motion compensation from the specified picture.
[0053]
Note that when performing encoding using the direct mode, instead of performing motion compensation with reference to encoded blocks having a positional relationship as shown in FIGS. It is also possible to perform motion compensation in the direct mode by setting the value of the motion vector of the target block to “0” and setting the picture to be referred to as the immediately preceding picture. By using this method, it is not necessary to perform a step of calculating a motion vector to be used in the direct mode, so that the encoding process can be simplified.
[0054]
At this time, instead of the spatial_flag indicating whether to perform temporal prediction or spatial prediction in the direct mode, the value of the motion vector of the encoding target block is set to “0” without referring to the encoded block. A flag indicating that motion compensation is performed may be described in the slice header.
[0055]
In the above method, among the motion vectors obtained by referring to the three blocks, a picture located closest to the current picture in display order among the pictures referred to by the three blocks is referred to. Although it is described that a motion vector is extracted, the present invention is not limited to this. For example, a motion vector referring to a picture closest to the current picture in the coding order may be extracted.
[0056]
(Embodiment 2)
A moving picture decoding method according to the second embodiment of the present invention will be described with reference to the block diagram shown in FIG. However, in the present moving picture decoding method, it is assumed that the code sequence generated by the moving picture coding method of Embodiment 1 is decoded.
[0057]
FIG. 8 is a block diagram illustrating a configuration of a moving picture decoding apparatus 200 according to the present embodiment. When the flag indicating the decoding method in the direct mode is “1”, the moving image decoding apparatus 200 performs the decoding using the spatial prediction on the decoding target block encoded in the direct mode. The decoding apparatus includes a code sequence analysis unit 201, a prediction residual decoding unit 202, a frame memory 203, a motion compensation decoding unit 204, a motion vector storage unit 205, a backward picture determination unit 206, an addition operation unit 207, and a switch 208. Is provided.
[0058]
The code sequence analysis unit 201 analyzes the input code sequence, extracts information such as prediction residual coded data, motion vector information and a prediction mode from the code sequence, and extracts the extracted motion vector information and prediction mode. The information is output to the motion compensation decoding unit 204 and the prediction residual coded data is output to the prediction residual decoding unit 202. The prediction residual decoding unit 202 performs variable-length decoding, inverse quantization, inverse frequency transformation, and the like on the extracted prediction residual encoded data to generate a prediction residual image.
[0059]
The frame memory 203 stores the decoded image in picture units, and outputs the stored pictures to an external monitor or the like as an output image in display order. The motion compensation decoding unit 204 performs decoding of a prediction mode and decoding of a motion vector used in the prediction mode, uses the decoded image stored in the frame memory 203 as a reference picture, and receives the input motion vector information. To generate a predicted image for the current block. When decoding the motion vector, the decoded motion vector stored in the motion vector storage unit 605 is used.
[0060]
The motion vector storage unit 205 stores the motion vector decoded by the motion compensation decoding unit 204. When the motion compensation decoding unit 204 generates the predicted image, the backward picture determining unit 206 determines whether or not a picture behind the current picture in display order has been decoded. Note that the backward picture determination unit 206 is used in the fourth embodiment, but is unnecessary in the present embodiment. The addition operation unit 207 adds the prediction residual image decoded by the prediction residual decoding unit 202 and the prediction image generated by the motion compensation decoding unit 204 to generate a decoded image of the decoding target block. I do.
[0061]
First, various information such as motion vector information and prediction residual coded data is extracted from the input code sequence by the code sequence analysis unit 201. The motion vector information extracted here is output to the motion compensation decoding unit 204, and the prediction residual coded data is output to the prediction residual decoding unit 202. The motion compensation decoding unit 204 uses the decoded image of the decoded picture stored in the frame memory 203 as a reference picture, and generates a predicted image based on the decoded motion vector.
[0062]
The prediction image generated in this way is input to the addition operation unit 207, and a decoded image is generated by performing addition with the prediction residual image generated in the prediction residual decoding unit 202. If the prediction direction is not restricted, the generated decoded image is rearranged in the order in which the pictures are displayed in the frame memory 203. However, if it is not possible to refer to a picture behind in the display order, It is possible to display the images in the order in which they have been decoded without rearrangement. In the above embodiment, the operation is performed on a code string on which inter-picture predictive encoding is performed. However, the switch 208 switches between decoding processing on a code string on which intra-picture predictive encoding is performed.
[0063]
The outline of the decoding flow has been described above, and the details of the processing in the motion compensation decoding unit 204 will be described below.
FIG. 9 is a flowchart showing a processing procedure of decoding in the direct mode in the motion compensation decoding unit 204 shown in FIG.
[0064]
The prediction mode and the motion vector information are added for each macroblock or each block obtained by dividing the macroblock. These pieces of information are described in the order of the macroblocks in the slice in the slice data area of the code string. If the prediction mode Mode indicates the direct mode, the motion compensation decoding unit 204 checks whether “0” or “1” is set in the flag spatial_flag to be decoded in the slice header (S901). ). When the subsequent picture is not decoded, the flag "spatial_flag" is set to "1", indicating that decoding is performed using spatial prediction.
[0065]
If the flag spatial_flag is set to “1”, the motion compensation decoding unit 204 creates a prediction image of the current block using spatial prediction in direct mode (S902), and sets “0”. If the prediction has been performed, the motion compensation decoding unit 204 creates a prediction image of the current block using temporal prediction in the direct mode (S903). When the prediction mode Mode in the slice header indicates a prediction mode other than the direct mode, the motion compensation decoding unit 204 sets a decoded picture as a reference picture for a macroblock to be decoded, A block in the reference picture is specified based on the decoded motion vector, and a predicted image for performing motion compensation is cut out from the specified block to generate a predicted image.
[0066]
Hereinafter, a specific method of the spatial prediction performed in step S902 of FIG. 9 will be described.
The example of the skip mode described with reference to FIG. 19 is for the case where the decoded block to be referred to has one motion vector at a time. However, among the prediction modes of the B picture, as shown in FIG. 2, there is also a mode in which the motion compensation is performed by simultaneously referring to two pictures ahead in the display order. In such a mode, one block has two motion vectors.
[0067]
FIG. 4 shows an example of a motion vector reference relationship in the case where a block having two motion vectors is included in a decoded block to which a motion vector is referred. Picture P94 is a picture currently being decoded, and block BL51 is a block for performing predictive decoding in the direct mode.
[0068]
First, as a first method, the motion compensation decoding unit 204 sets the block BL51 (or the block BL51 (or the block BL51) to perform the predictive decoding in the direct mode in both cases shown in FIGS. 18A and 18B. BL52) basically refers to the motion vector of the block at the position of A, B, C. However, the reference is changed according to the following conditions.
[0069]
1. If the block C cannot be referred to, the block at the positions A, B, and D is referred to.
If there is a block that cannot refer to a motion vector among the three blocks located at 2, A, B, and C, or A, B, and D, the block is excluded from motion vector reference targets.
[0070]
The motion compensation decoding unit 204 determines which of the motion vectors of the three blocks A, B, and C (or A, B, and D) has been referred to by the motion vector and the decoding target picture. Compare the perspective in the display order with. From the comparison, a motion vector that refers to a picture located closest to the current picture in display order from the decoding target picture is extracted. When there are a plurality of extracted motion vectors, the median value or the average value thereof is taken. For example, a median value may be taken when there are an odd number of extracted motion vectors, and an average value may be taken when there are even numbered motion vectors.
[0071]
The motion vector obtained in this way is used as the motion vector of the current block to be decoded when the direct mode is selected, in the case where the motion compensation is performed by referring to only the picture preceding the current picture in the display order. . If all the blocks A, B, and C (or A, B, and D) cannot be referred to, the motion vector of the current block is set to 0, and the picture to be referred to is set as the immediately preceding picture. I do.
[0072]
The flowchart in FIG. 5 illustrates an example of a processing procedure when the motion compensation decoding unit 204 illustrated in FIG. 8 performs the spatial prediction of the current block using the first method. Hereinafter, the decoding target block BL51 illustrated in FIG. 4 will be described as an example.
[0073]
First, the motion compensation decoding unit 204 checks whether or not the block at the position C can be referred to with respect to the decoding target block BL51 (S601). In FIG. 4, the block at the position C has a motion vector MVC1 referring to the picture P93 and a motion vector MVC2 referring to the picture P92. Therefore, the motion compensation decoding unit 204 refers to the motion vectors of the blocks at the positions of A, B, and C (S602).
[0074]
The block at the position A has a motion vector MVA1 referring to the picture P93, and the block at the position B has a motion vector MVB1 referring to the picture P93 and a motion vector MVB3 referring to the picture P91. In step S601, the block at the position C is outside the decoding target picture P94, outside the slice to which the decoding target block BL51 belongs, or because decoding such as intra prediction has been performed. If there is no motion vector, the motion vector of the block at the position D shown in FIGS. 18A and 18B is referred to instead of the block at the position C (S603). That is, three blocks at positions A, B, and D are referred to.
[0075]
Next, the motion compensation decoding unit 204 is outside the decoding target picture P94 among the three referenced blocks (A, B, C or A, B, D), or the decoding target block BL51 belongs. If the block does not have a motion vector due to being outside the slice or having undergone decoding such as intra prediction, the block is excluded from the reference candidates and the motion vector of the decoding target block is calculated. (S604).
[0076]
When all blocks cannot be referred to among the three blocks (A, B, C or A, B, D), the motion vector of the current block is set to “0” and the motion vector immediately before the current picture to be decoded is set to “0”. Refers to a picture. The motion compensation decoding unit 204 extracts, from these referenced motion vectors, only those that refer to the picture closest to the decoding target picture in display order, the motion vector MVA1 and the motion vector MVB1 that refer to the picture P93. And the motion vector MVC1. The motion compensation decoding unit 204 further takes a median value or an average value. For example, in this case, since three motion vectors are obtained, a median value is obtained. Thereby, one motion vector MV1 for performing motion compensation of the block BL51 can be determined.
[0077]
As described above, in the above-described embodiment, even in an environment where it is not possible to refer to a picture located backward in the display order, it is possible to directly refer to a picture located backward in the display order when performing predictive decoding using the direct mode. A method to realize the mode was proposed, and a decoding method to achieve high coding efficiency was shown.
[0078]
Note that, in the first method, among the referenced motion vectors, the one that refers to the picture closest to the decoding target picture in display order is extracted. Only the picture that refers to the immediately preceding picture may be extracted. In the case of the example shown in FIG. 4, among the pictures referenced by the referenced motion vector, the picture closest to the current picture in display order is the picture immediately before the current picture to be decoded. The vectors are the same. If there is no motion vector that refers to the closest picture in the display order, the decoding is performed in the direct mode with the motion vector of the decoding target block set to “0”.
[0079]
Further, in the first method, when determining a motion vector to be used in the direct mode, by referring to a picture located in the foreground from a decoding target picture in display order from among pictures referred to by neighboring decoded blocks. Only one motion vector is taken out and one motion vector is finally calculated. Instead, as a second method, a motion vector referring to N pictures before the current picture in decoding order is displayed. One motion vector is determined for each picture taken out and referred to, and the obtained N motion vectors are subjected to motion compensation for referencing only the forward direction as motion vectors used for predictive decoding in the direct mode. It is also possible. At this time, the predicted image is generated by calculating the average of the pixel values of N regions specified by the N motion vectors.
[0080]
Note that it is also possible to generate a predicted image by a method of averaging by weighting the pixel values of each area instead of a simple average. By using this method, it is possible to realize more accurate motion compensation for an image sequence in which pixel values gradually change in display order.
[0081]
FIG. 7 illustrates an example of a motion vector reference method in a case where two motion vectors are calculated by extracting a motion vector that refers to two pictures from the front of the current picture in the display order. Picture P104 is a picture currently being decoded, and BL51 is a block for performing predictive decoding in the direct mode. Using the motion vector MVA1, the motion vector MVB1, and the motion vector MVC1 that refer to the picture P103 that is the closest in the display order among the pictures referenced by the plurality of motion vectors to be referred to, the median value or The motion vector MV1 is determined by taking the average value, and the median value or the average value of the motion vectors referring to the picture P102 which is two in front in the display order, that is, the motion vector MV2 is determined by taking MVC2 itself. Then, decoding in the direct mode is performed using these two motion vectors.
[0082]
It should be noted that instead of using only the one that refers to one or N pictures from the front in the display order from among the motion vectors of the blocks referred to in FIGS. 18A and 18B, It is also possible to take out only the motion vector referring to the specified picture, determine the value of the motion vector of the current block to be used in the direct mode, and perform motion compensation from the specified picture.
[0083]
When decoding is performed using the direct mode, instead of performing motion compensation with reference to encoded blocks having a positional relationship as shown in FIGS. 18A and 18B, decoding is performed. It is also possible to perform motion compensation in the direct mode by setting the value of the motion vector of the target block to “0” and setting the picture to be referred to as the immediately preceding picture. By using this method, it is not necessary to perform a step of calculating a motion vector to be used in the direct mode, so that the decoding process can be simplified.
[0084]
In the corresponding encoding process, a flag indicating that motion compensation is performed with the value of the motion vector of the encoding target block set to “0” without referring to the encoded block in the direct mode has been encoded. In this case, by interpreting the value of the flag, the operation can be switched to the operation and the motion prediction in the direct mode can be performed.
[0085]
In the above method, among the motion vectors obtained by referring to the three blocks, the picture closest to the decoding target picture in the display order among the pictures referred to by them is referred to. Although it is described that a motion vector is extracted, the present invention is not limited to this. For example, a motion vector referring to a picture closest to the current picture in decoding order may be extracted.
[0086]
(Embodiment 3)
The moving picture coding method according to the third embodiment of the present invention will be described with reference to the block diagram shown in FIG.
A moving image to be encoded is input to the frame memory 101 in picture order in time order. Each picture is divided into, for example, a block of 16 × 16 pixels, which is called a macroblock, and the subsequent processing is performed in block units.
[0087]
The macroblock read from the frame memory 101 is input to the motion vector detection unit 106. Here, a motion vector of a macroblock to be coded is detected using a decoded picture of a coded picture stored in the frame memory 105 as a reference picture.
[0088]
The mode selection unit 107 determines the optimal prediction mode while referring to the motion vector used in the coded picture stored in the motion vector storage unit 108. At this time, the backward picture determination unit 109 determines whether or not the picture behind in the display order has already been coded. If it is determined that the backward picture has not been coded, A prediction mode that refers to a picture located backward in the display order is restricted so as not to be selected.
[0089]
FIG. 10 shows an example of a table that associates a code for identifying a prediction mode in a B picture with an encoding mode. If the prediction direction is not restricted, a table indicating all the reference patterns is used as shown in FIG. 10A, but if the prediction direction is restricted only to the front, the table shown in FIG. Recreate the table with all the referenced patterns removed and refer to it. This makes it possible to reduce the amount of bits required for the code for identifying the prediction mode. Each item in the tables of FIG. 10A and FIG. 10B can be handled in the same manner when other values are used.
[0090]
FIG. 2 shows the reference relationship of each picture when it is not possible to refer to the picture behind in the display order. All the B pictures included in the sequence are subjected to predictive encoding with reference to one or a plurality of encoded pictures located ahead in the display order.
[0091]
The prediction image determined by the obtained motion vector is input to the difference calculation unit 110, and a difference from the coding target macroblock is calculated to generate a prediction residual image. Is performed. The above processing flow is the operation when the inter-picture prediction coding is selected. However, the switch 112 switches to the intra-picture prediction coding. Finally, the code string generation unit 103 performs variable length coding on control information such as a motion vector and image information output from the prediction residual coding unit 102, and generates a finally output code string. You.
[0092]
The outline of the flow of the encoding has been described above. The details of the processing in the motion vector detecting unit 106 and the mode selecting unit 107 will be described below. Here, it is assumed that the rear picture determination unit 109 determines that the rear picture is not coded.
[0093]
The detection of a motion vector is performed for each macroblock or for each region obtained by dividing the macroblock. For a macroblock to be coded, a predicted image is created by determining a motion vector indicating a position predicted to be optimal in a search area within the picture and a prediction mode by using a previously coded picture as a reference picture. .
[0094]
If the direct mode is selected by the mode selection unit 107 when predictive encoding of a B picture is performed in an environment in which a picture backward in the display order is not encoded, the immediately following picture is displayed in the display order described in the related art. Instead of using a picture as a motion vector with reference to a picture, a direct mode is realized by referring to a motion vector of a coded block located around a block to be coded.
[0095]
First, a case will be described in which each of the encoded blocks located around the current block has one motion vector. FIG. 18 shows the positional relationship of the referenced blocks. FIG. 18A shows an example in which a block BL51 for encoding in the direct mode has a size of 16 × 16 pixels, and FIG. 18B shows a block BL52 for encoding in the direct mode. This is an example of a case where the size is 8 pixels × 8 pixels. In any case, basically, the motion vectors of three blocks having a positional relationship of A, B, and C are referred to. However, in the case of the following conditions, the reference is not performed, the motion vector value of the current block is set to “0”, and the motion compensation in the direct mode is performed by referring to the immediately preceding picture.
[0096]
1. When A or B is outside the picture or outside the slice.
2. A or B has a motion vector of a value “0” referring to the immediately preceding picture.
From the motion vectors of the three blocks A, B, and C that have been referred to, only those that refer to the immediately preceding picture are extracted, and the median or average value is used to actually use it in the direct mode. Let it be a motion vector. However, when the block C cannot be referred to, the block D is used instead.
[0097]
FIG. 19 shows an example of the reference relationship between the motion vectors at that time. It is assumed that a block BL51 belonging to the picture P64 is a currently coded block. In this example, the motion vector referring to the immediately preceding picture is only MVA1, and the value of MVA1 is used as it is as the motion vector MV1 used in the direct mode. Note that the positional relationship of the blocks to be referred to is the same when a place other than A, B, C, and D shown in FIGS. 18A and 18B is used.
[0098]
The example of FIG. 19 is for the case where the encoded block to be referenced has one motion vector at a time. However, some of the B picture prediction modes perform motion compensation by simultaneously referring to two pictures ahead in the display order. In such a mode, one block has two motion vectors.
[0099]
Hereinafter, a case will be described in which a coded block located around the current block includes a block having two motion vectors. FIG. 4 is a diagram illustrating an example of a reference relationship between motion vectors when a block having two motion vectors is included in a coded block located around the current block. The picture P94 is a picture currently being coded, and the block BL51 is a block for performing predictive coding in the direct mode. Of the pictures referenced by all the motion vectors of the block to be referred to, the motion vectors MVA1, MVB1, and MVC1 referencing the picture P93, which is the picture immediately before in the display order, are used. By taking the median value or the average value, the motion vector MV1 used for predictive coding in the direct mode is determined, and motion compensation is performed by referring only to the forward direction.
[0100]
As described above, in the above embodiment, even in an environment where it is not possible to refer to a picture located backward in the display order, it is possible to directly refer to a picture located backward in the display order when performing predictive encoding using the direct mode. A method for realizing a mode is proposed, and the number of items in the table can be reduced by removing an item that refers to a subsequent picture from the table of the encoding mode. showed that.
[0101]
When deciding a motion vector to be used in the direct mode, only a motion vector referring to a picture located closest to the display order in the display order is extracted from among pictures referred to by neighboring encoded blocks, and one motion vector is extracted. Instead of calculating the vectors, a motion vector referring to N pictures is extracted from the near side, one motion vector is determined for each picture referred to, and the obtained N motion vectors are determined in the direct mode. It is also possible to perform motion compensation that refers only to the forward direction as a motion vector used for predictive coding of. At this time, the predicted image is generated by calculating the average of the pixel values of N regions specified by the N motion vectors.
[0102]
Note that it is also possible to generate a predicted image by a method of averaging by weighting the pixel values of each area instead of a simple average. By using this method, it is possible to realize more accurate motion compensation for an image sequence in which pixel values gradually change in display order.
[0103]
FIG. 7 shows an example of a motion vector reference method when N = 2 in the above case. P104 is a picture currently being coded, and BL51 is a block for performing predictive coding in the direct mode. Using the motion vectors MVA1, MVB1, and MVC1 referencing the foremost picture P103 in the display order among the pictures referenced by the plurality of motion vectors to be referred to, take the median or average value thereof. Thus, the motion vector MV1 is determined, and furthermore, the motion vector MV2 is determined by taking the median value or the average value of the motion vectors referring to the picture P102 which is two immediately preceding in the display order, that is, MVC2 itself. The coding in the direct mode is performed using one motion vector.
[0104]
It should be noted that the following conditions can be used instead of the method described in the above embodiment as a method of determining a block to which a motion vector is referred in FIGS. 18A and 18B.
When 1, A and D cannot be referred to, those motion vectors are referred to as "0".
If 2, B, C and D cannot be referenced, only A is referenced.
If only 3 and C cannot be referenced, A, B and D are referenced.
4. In cases other than 2 and 3 above, reference is made to A, B and C.
[0105]
It should be noted that instead of using only the one that refers to one or N pictures from the front in the display order from among the motion vectors of the blocks referred to in FIGS. 18A and 18B, It is also possible to take out only the motion vector referring to the specified picture, determine the value of the motion vector of the current block to be used in the direct mode, and perform motion compensation from the specified picture.
[0106]
When performing encoding using the direct mode, instead of performing motion compensation with reference to blocks having a positional relationship as shown in FIG. 18A and FIG. It is also possible to perform motion compensation in the direct mode with the value of the vector being “0” and the picture to be referred to as the immediately preceding picture. By using this method, it is not necessary to perform a step of calculating a motion vector to be used in the direct mode, so that the encoding process can be simplified.
[0107]
In the above embodiment, among the motion vectors obtained by referring to the three blocks, the picture closest to the encoding target picture in the display order among the pictures referred to by them is referred to. Although it is described that the motion vector is extracted, the present invention is not limited to this. For example, a motion vector referring to a picture closest to the current picture in the coding order may be extracted.
[0108]
(Embodiment 4)
A moving picture decoding method according to the fourth embodiment of the present invention will be described with reference to the block diagram shown in FIG. However, it is assumed that a code string generated by the moving picture coding method according to the third embodiment is input.
[0109]
First, various information such as motion vector information and prediction residual coded data is extracted from the input code sequence by the code sequence analysis unit 201. The motion vector information extracted here is output to the motion compensation decoding unit 204, and the prediction residual coded data is output to the prediction residual decoding unit 202. The motion compensation decoding unit 204 uses the decoded image of the decoded picture stored in the frame memory 203 as a reference picture, and generates a predicted image based on the input motion vector information. At this time, the backward picture determination unit 206 determines whether or not the picture behind in the display order has already been coded. If it is determined that the backward picture has not been coded, A prediction mode that refers to a picture located backward in the display order is restricted so as not to be selected.
[0110]
FIG. 10 shows an example of a table that associates a code for identifying a prediction mode in a B picture with an encoding mode. If the prediction direction is not restricted, a table indicating all the reference patterns is used as shown in FIG. 10A, but if the prediction direction is restricted only to the front, the table shown in FIG. Recreate the table with all the referenced patterns removed and refer to it. Each item in the tables of FIG. 10A and FIG. 10B can be handled in the same manner when other values are used.
[0111]
The prediction image generated in this way is input to the addition operation unit 207, and a decoded image is generated by performing addition with the prediction residual image generated in the prediction residual decoding unit 202. If the prediction direction is not restricted, the generated decoded image is rearranged in the order in which the pictures are displayed in the frame memory 203, but if it is not possible to refer to the backward picture in the display order, It is possible to display the images in the order in which they have been decoded without rearrangement. In the above-described embodiment, the operation is performed on a code string that has been subjected to inter-picture predictive coding. However, the switch 208 switches between the decoding processing for a code string that has been subjected to intra-picture predictive coding.
[0112]
The outline of the decoding flow has been described above, and the details of the processing in the motion compensation decoding unit 204 will be described below. Here, it is assumed that the backward picture determination unit 206 determines that the backward picture is not decoded.
The motion vector information is added for each macroblock or each region obtained by dividing the macroblock. For a macroblock to be decoded, a picture that has already been decoded is used as a reference picture, and a predicted image for performing motion compensation is created from within the picture using the decoded motion vector.
[0113]
When the direct mode is specified in the predictive decoding of a B picture in an environment in which the backward picture in the display order is not decoded, the motion vector is referred to by referring to the immediately succeeding picture in the display order described in the related art. Instead of using it, the direct mode is realized by referring to the motion vector of a decoded block located around the block to be decoded.
[0114]
First, a case will be described in which each of the decoded blocks located around the current block has one motion vector. FIG. 18 shows the positional relationship of the referenced blocks. FIG. 18A shows an example in which a block BL51 for decoding in the direct mode has a size of 16 pixels × 16 pixels, and FIG. 18B shows a block BL52 for decoding in the direct mode. This is an example of a case where the size is 8 pixels × 8 pixels. In any case, basically, the motion vectors of three blocks having a positional relationship of A, B, and C are referred to. However, in the case of the following conditions, the reference is not performed, and the motion vector value of the decoding target block is set to “0”, and the motion compensation in the direct mode is performed by referring to the immediately preceding picture.
1. When A or B is outside the picture or outside the slice.
2. A or B has a motion vector of a value “0” referring to the immediately preceding picture.
[0115]
From the motion vectors of the three blocks A, B, and C that have been referred to, only those that refer to the immediately preceding picture are extracted, and the median or average value is used to actually use it in the direct mode. Let it be a motion vector. However, when the block C cannot be referred to, the block D is used instead.
[0116]
FIG. 19 shows an example of the reference relationship between the motion vectors at that time. It is assumed that a block BL51 belonging to the picture P64 is a block currently being decoded. In this example, the motion vector referring to the immediately preceding picture is only MVA1, and the value of MVA1 is used as it is as the motion vector MV1 used in the direct mode. Note that the positional relationship of the blocks to be referred to is the same when a place other than A, B, C, and D shown in FIGS. 18A and 18B is used.
[0117]
The example in FIG. 19 is for the case where the decoded block to be referred to has one motion vector at a time. However, some of the B picture prediction modes perform motion compensation by simultaneously referring to two pictures ahead in the display order. In such a mode, one block has two motion vectors.
[0118]
Hereinafter, a case will be described where a decoded block located around a current block to be decoded includes a block having two motion vectors. FIG. 4 shows an example of a reference relationship between motion vectors in such a case. P94 is a picture currently being decoded, and BL51 is a block for performing predictive decoding in the direct mode. Among the pictures referenced by all the motion vectors of the block to be referenced, the motion vectors MVA1, MVB1, and MVC1 referencing the picture P93, which is the picture immediately before in the display order. By taking the median value or the average value, the motion vector MV1 used for predictive decoding in the direct mode is determined, and motion compensation is performed with reference to only the forward direction.
[0119]
As described above, in the above-described embodiment, even in an environment where it is not possible to refer to a picture located backward in the display order, it is possible to directly refer to a picture located backward in the display order when performing predictive decoding using the direct mode. A method for realizing the mode is proposed, and a decoding method for realizing high encoding efficiency by reducing the number of items in the table by removing items referring to the subsequent picture from the encoding mode table is shown.
[0120]
When deciding a motion vector to be used in the direct mode, only a motion vector referring to a picture located closest to the display order in the display order is extracted from among pictures referred to by neighboring decoded blocks, and one motion vector is extracted. Instead of calculating the vectors, a motion vector referring to N pictures is extracted from the near side, one motion vector is determined for each picture referred to, and the obtained N motion vectors are determined in the direct mode. It is also possible to perform motion compensation that refers only to the forward direction as a motion vector used for predictive decoding of. At this time, the predicted image is generated by calculating the average of the pixel values of N regions specified by the N motion vectors.
[0121]
Note that it is also possible to generate a predicted image by a method of averaging by weighting the pixel values of each area instead of a simple average. By using this method, it is possible to realize more accurate motion compensation for an image sequence in which pixel values gradually change in display order.
[0122]
FIG. 7 shows an example of a motion vector reference method when N = 2 in the above case. P104 is a picture currently being decoded, and BL51 is a block for performing predictive decoding in the direct mode. Using the motion vectors MVA1, MVB1, and MVC1 referencing the foremost picture P103 in the display order among the pictures referenced by the plurality of motion vectors to be referred to, take the median or average value thereof. Thus, the motion vector MV1 is determined, and furthermore, the motion vector MV2 is determined by taking the median value or the average value of the motion vectors referring to the picture P102 which is two immediately preceding in the display order, that is, MVC2 itself. Decoding in direct mode is performed using two motion vectors.
[0123]
It should be noted that the following conditions can be used instead of the method described in the above embodiment as a method of determining a block to which a motion vector is referred in FIGS. 18A and 18B.
When 1, A and D cannot be referred to, those motion vectors are referred to as "0".
If 2, B, C and D cannot be referenced, only A is referenced.
If only 3 and C cannot be referenced, A, B and D are referenced.
4. In cases other than 2 and 3 above, reference is made to A, B and C.
[0124]
It should be noted that instead of using only the one that refers to one or N pictures from the front in the display order from among the motion vectors of the blocks referred to in FIGS. 18A and 18B, It is also possible to take out only the motion vector referring to the specified picture, determine the value of the motion vector of the current block to be used in the direct mode, and perform motion compensation from the specified picture.
[0125]
When performing decoding using the direct mode, instead of performing motion compensation with reference to blocks having a positional relationship as shown in FIG. 18A and FIG. It is also possible to perform motion compensation in the direct mode with the value of the vector being “0” and the picture to be referred to as the immediately preceding picture. By using this method, it is not necessary to perform a step of calculating a motion vector to be used in the direct mode, so that the decoding process can be simplified.
[0126]
(Embodiment 5)
Furthermore, by recording a program for realizing the configuration of the moving picture encoding method or the moving picture decoding method shown in the above-described embodiment on a recording medium such as a flexible disk, the first embodiment can be used. Can be easily implemented in an independent computer system.
[0127]
FIG. 11 is an explanatory diagram of a case where the present invention is implemented by a computer system using a flexible disk storing the moving picture coding method or the moving picture decoding method according to the first embodiment.
[0128]
FIG. 11B shows the appearance, cross-sectional structure, and flexible disk of the flexible disk as viewed from the front, and FIG. 11A shows an example of the physical format of the flexible disk which is a recording medium body. The flexible disk FD is built in the case F, and a plurality of tracks Tr are formed concentrically from the outer circumference toward the inner circumference on the surface of the disk, and each track is divided into 16 sectors Se in an angular direction. ing. Therefore, in the flexible disk storing the program, the moving image encoding method as the program is recorded in an area allocated on the flexible disk FD.
[0129]
FIG. 11C shows a configuration for recording and reproducing the program on the flexible disk FD. When the above program is recorded on the flexible disk FD, the moving picture encoding method or the moving picture decoding method as the above program is written from the computer system Cs via the flexible disk drive. When the moving picture encoding method is constructed in a computer system using 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.
[0130]
In the above description, the description has been made using a flexible disk as a recording medium. However, the same description can be made using an optical disk. Further, the recording medium is not limited to this, and the present invention can be similarly implemented as long as the program can be recorded, such as an IC card or a ROM cassette.
[0131]
(Embodiment 6)
Further, here, application examples of the moving picture coding method and the moving picture decoding method described in the above embodiment and a system using the same will be described.
[0132]
FIG. 12 is a block diagram illustrating an overall configuration of a content supply system ex100 that realizes a content distribution service. A communication service providing area is divided into desired sizes, and base stations ex107 to ex110, which are fixed wireless stations, are installed in each cell.
[0133]
The content supply system ex100 includes, for example, a computer ex111, a PDA (personal digital assistant) ex112, a camera ex113, a mobile phone ex114, and a camera via the Internet ex101 via the Internet service provider ex102 and the telephone network ex104, and the base stations ex107 to ex110. Each device such as a mobile phone ex115 with a tag is connected.
[0134]
However, the content supply system ex100 is not limited to the combination as shown in FIG. 12, and may be connected in any combination. 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.
[0135]
The camera ex113 is a device such as a digital video camera capable of shooting moving images. In addition, a mobile phone can be a PDC (Personal Digital Communications) system, a CDMA (Code Division Multiple Access) system, a W-CDMA (Wideband-Code Division Multiple Access mobile phone system, or a GSM gigabit mobile access system). Or PHS (Personal Handyphone System) or the like.
[0136]
The streaming server ex103 is connected from the camera ex113 to the base station ex109 and the telephone network ex104, and enables live distribution and the like based on encoded data transmitted by the user using the camera ex113. The encoding process of the photographed data may be performed by the camera ex113, or may be performed by a server or the like that performs the data transmission process.
[0137]
Also, moving image data captured by the camera ex116 may be transmitted to the streaming server ex103 via the computer ex111. The camera ex116 is a device such as a digital camera that can shoot still images and moving images. In this case, encoding of the moving image data may be performed by the camera ex116 or the computer ex111. The encoding process is performed by the LSI ex117 of the computer ex111 and the camera ex116.
[0138]
The moving image encoding / decoding software may be incorporated in any storage medium (a CD-ROM, a flexible disk, a hard disk, or the like) that is a recording medium readable by the computer ex111 or the like. Further, the moving image data may be transmitted by the mobile phone with camera ex115. The moving image data at this time is data encoded by the LSI included in the mobile phone ex115.
[0139]
In the content supply system ex100, the content (for example, a video image of a live music) captured by the user with the camera ex113, the camera ex116, or the like is encoded and transmitted to the streaming server ex103 as in the above-described embodiment. On the other hand, the streaming server ex103 stream-distributes the content data to the requesting 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.
[0140]
In this way, the content supply system ex100 can receive and reproduce the encoded data at the client, and further, realizes personal broadcast by receiving, decoding, and reproducing the data in real time at the client. It is a system that becomes possible.
[0141]
The encoding and decoding of each device constituting this system may be performed using the video encoding device or the video decoding device described in each of the above embodiments.
A mobile phone will be described as an example.
[0142]
FIG. 13 is a diagram illustrating 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 unit ex203 capable of taking a picture such as a CCD camera, a still image, a picture taken by the camera unit ex203, and an antenna ex201. A display unit ex202 such as a liquid crystal display for displaying data obtained by decoding a received video or the like, a main unit including operation keys ex204, an audio output unit ex208 such as a speaker for outputting audio, and audio input. Input unit ex205 such as a microphone for storing encoded or decoded data, such as data of captured moving images or still images, received mail data, moving image data or still image data, etc. Of recording media ex207 to mobile phone ex115 And a slot portion ex206 to ability. The recording medium ex207 stores a flash memory device, which is a kind of electrically erasable and programmable read only memory (EEPROM), which is a nonvolatile memory that can be electrically rewritten and erased, in a plastic case such as an SD card.
[0143]
Further, the mobile phone ex115 will be described with reference to FIG. The mobile phone ex115 is provided with a power supply circuit unit ex310, an operation input control unit ex304, an image encoding unit, and a main control unit ex311 which controls the respective units of a main body unit including a display unit ex202 and operation keys 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 the synchronous bus ex313. Connected to each other.
[0144]
When the end of the call and the power key are turned on by a user operation, the power supply circuit unit ex310 supplies power to each unit from the battery pack to activate the digital cellular phone with camera ex115 in an operable state. .
[0145]
The mobile phone ex115 converts a sound signal collected by the sound input unit ex205 into digital sound data by the sound processing unit ex305 in the voice call mode based on the control of the main control unit ex311 including a CPU, a ROM, a RAM, and the like. This is spread-spectrum-processed by a modulation / demodulation circuit unit ex306, subjected to digital-analog conversion processing and frequency conversion processing by a transmission / reception circuit unit ex301, and then transmitted via an antenna ex201. The mobile phone ex115 amplifies the received data received by the antenna ex201 in the voice communication mode, performs frequency conversion processing and analog-to-digital conversion processing, performs spectrum despreading processing in the modulation / demodulation circuit unit ex306, and performs analog voice decoding in the voice processing unit ex305. After being converted into data, this is output via the audio output unit ex208.
[0146]
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 transmits the data to the base station ex110 via the antenna ex201.
[0147]
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, 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.
[0148]
The image encoding unit ex312 includes the moving image encoding device described in the present invention, and encodes image data supplied from the camera unit ex203 using the moving image encoding device described in the above embodiment. The image data is converted into encoded image data by performing compression encoding according to a demultiplexing method, and is transmitted to the demultiplexing unit ex308. At this time, the mobile phone ex115 simultaneously transmits the audio 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.
[0149]
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 multiplexes the resulting multiplexed data into a modulation / demodulation circuit unit. The signal is subjected to spread spectrum processing in ex306 and subjected to digital-analog conversion processing and frequency conversion processing in the transmission / reception circuit unit ex301, and then transmitted via the antenna ex201.
[0150]
When data of a moving image file linked to a homepage or the like is received in the data communication mode, the 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 multiplexed data is obtained. The demultiplexed data is sent to the demultiplexing unit ex308.
[0151]
To decode the 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 performs synchronization. The coded 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.
[0152]
Next, the image decoding unit ex309 is configured to include the moving image decoding device described in the present invention, and converts a bit stream of image data into a decoding method corresponding to the encoding method described in the above embodiment. By decoding, reproduced moving image data is generated and supplied to the display unit ex202 via the LCD control unit ex302, whereby, for example, moving image data included in a moving image file linked to a homepage is displayed. At this time, the audio processing unit ex305 simultaneously converts the audio data into analog audio data and supplies the analog audio data to the audio output unit ex208, whereby the audio data included in the moving image file linked to the homepage is reproduced, for example. You.
[0153]
It should be noted that the present invention is not limited to the example of the system described above, and digital broadcasting using satellites and terrestrial waves has recently become a topic. As shown in FIG. Any of the video decoding devices can be incorporated. Specifically, at the broadcasting station ex409, the bit stream of the video information is transmitted to the communication or the broadcasting satellite ex410 via radio waves. The broadcasting satellite ex410 receiving this transmits a radio wave for broadcasting, receives this radio wave with a home antenna ex406 having a satellite broadcasting receiving facility, and transmits the radio wave to a television (receiver) ex401 or a set-top box (STB) ex407 or the like. The device decodes the bit stream and reproduces it.
[0154]
Further, the moving picture decoding apparatus described in the above embodiment can also be mounted on a reproducing apparatus ex403 that reads and decodes a bit stream recorded on a storage medium ex402 such as a CD or DVD, which is a recording medium. . In this case, the reproduced video signal is displayed on the monitor ex404. A configuration is also conceivable 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 of the television. At this time, the moving picture decoding device may be incorporated in the television instead of the set-top box.
[0155]
Further, it is also possible to receive a signal from the satellite ex410 or the base station ex107 or the like with the car ex412 having the antenna ex411 and reproduce the moving image on a display device such as the car navigation ex413 or the like included in the car ex412.
[0156]
Further, an image signal can be encoded by the moving image encoding device described in the above embodiment and recorded on a recording medium. As specific examples, there are a recorder ex420 such as a DVD recorder for recording an image signal on a DVD disk ex421 and a disk recorder for recording on a hard disk. Furthermore, it can be recorded on the SD card ex422. If the recorder ex420 includes the moving picture decoding device described in the above embodiment, the video signal recorded on the DVD disc ex421 or the SD card ex422 can be reproduced and displayed on the monitor ex408.
[0157]
The configuration of the car navigation system ex413 may be, for example, a configuration excluding the camera unit ex203, the camera interface unit ex303, and the image encoding unit ex312 from the configuration illustrated in FIG. 14, and the same applies to the computer ex111 and the television (receiver). ) Ex401 and the like can also be considered.
[0158]
In addition, terminals such as the mobile phone ex114 and the like have three mounting formats, in addition to a transmitting / receiving terminal having both an encoder and a decoder, a transmitting terminal having only an encoder and a receiving terminal having only a decoder. Can be considered.
As described above, the moving picture coding method or the moving picture decoding method described in the above embodiment can be used for any of the devices and systems described above. The effect can be obtained.
[0159]
Further, the present invention is not limited to the above embodiment, and various changes or modifications can be made without departing from the scope of the present invention.
INDUSTRIAL APPLICABILITY The moving picture coding apparatus according to the present invention is useful as a moving picture coding apparatus provided in a personal computer, a PDA, a digital broadcast station, a mobile phone, and the like having a communication function.
[0160]
Further, the moving picture decoding apparatus according to the present invention is useful as a moving picture decoding apparatus provided in a personal computer having a communication function, a PDA, an STB for receiving digital broadcasts, and a mobile phone.
[0161]
【The invention's effect】
As described above, according to the moving picture coding method of the present invention, even in an environment where a picture that is temporally backward cannot be referred to, the picture that is temporally backward when predictive encoding is performed using the direct mode. To reduce the number of items in the table and realize high encoding efficiency by removing the items that refer to the subsequent pictures from the encoding mode table. Make it possible.
[0162]
Further, according to the moving picture decoding method of the present invention, even in an environment where it is not possible to refer to a temporally backward picture, the temporally backward picture is referred to when performing predictive decoding using the direct mode. A method for realizing the direct mode without using the encoding mode, and further reducing the number of items in the table by removing the items referring to the subsequent pictures from the encoding mode table, and encoding a code sequence encoded with high encoding efficiency. Can be decoded without contradiction.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a video encoding device that executes a video encoding method according to Embodiment 1.
FIG. 2 is a diagram illustrating an example of a reference relationship between pictures in a case where it is not possible to refer to a picture behind a picture to which an encoding target block belongs in display order.
FIG. 3 is a flowchart illustrating an example of an operation of a mode selection unit when a direct mode is selected.
FIG. 4 is a diagram illustrating an example of a motion vector reference relationship in a case where a block having two motion vectors is included in an encoded block to which a motion vector is referred;
5 is a flowchart illustrating an example of a processing procedure in a case where the mode selection unit illustrated in FIG. 1 performs spatial prediction of an encoding target block using the first method.
FIG. 6 is a diagram illustrating an example of a data structure of each slice of a code string generated by the code string generation unit illustrated in FIG. 1;
FIG. 7 is a diagram illustrating an example of a motion vector referencing method in a case where two motion vectors are calculated by extracting a motion vector referring to two pictures from a position before a current picture in a display order.
FIG. 8 is a block diagram illustrating a configuration of a video decoding device according to the present embodiment.
FIG. 9 is a flowchart showing a decoding procedure in a direct mode in the motion compensation decoding unit shown in FIG. 8;
FIG. 10A is a diagram illustrating an example of a table that associates a code for identifying a prediction mode in a B picture with an encoding mode.
(B) is a diagram illustrating an example of a table that associates a code for identifying a prediction mode in a B picture with a coding mode when the prediction direction is restricted to only the forward direction.
FIG. 11A is a diagram illustrating an example of a physical format of a flexible disk as a recording medium body.
FIG. 2B is a diagram showing the appearance, cross-sectional structure, and flexible disk of the flexible disk as viewed from the front.
(C) is a diagram showing a configuration for recording and reproducing the program on a flexible disk FD.
FIG. 12 is a block diagram illustrating an overall configuration of a content supply system that realizes a content distribution service.
FIG. 13 is a diagram illustrating an example of an appearance of a mobile phone.
FIG. 14 is a block diagram illustrating a configuration of a mobile phone.
FIG. 15 is a diagram illustrating a device that performs the encoding process or the decoding process described in the above embodiment, and a system using the device.
FIG. 16 is a diagram illustrating an example of a reference relationship between each picture and a picture referred to by the picture in the conventional moving picture coding method.
17 (a) is a diagram showing a picture in the display order extracted from a picture around a picture B18 shown in FIG. 16; FIG.
FIG. 18B is a diagram illustrating the encoding order of the peripheral pictures of the picture B18 when the picture B18 is encoded based on the reference relationship illustrated in FIG.
FIG. 18 is a diagram showing a positional relationship between a coded block whose motion vector is referred to and a current block when referring to a motion vector of a coded block located around the current block in the same picture. is there.
(A) This is an example where the target block BL51 has a size of 16 pixels × 16 pixels.
(B) This is an example when the target block BL52 has a size of 8 pixels × 8 pixels.
FIG. 19 is a diagram illustrating an example of a motion vector referred to in a skip mode of a P picture and an encoded picture referred to by the motion vector.
FIG. 20 is a diagram illustrating a method for determining a motion vector in the direct mode.
[Explanation of symbols]
100 Moving picture coding device
101 frame memory
102 prediction error encoding unit
103 Code string generation unit
104 prediction residual decoding unit
105 frame memory
106 motion vector detection unit
107 Mode selector
108 Motion vector storage unit
109 Back picture determination unit
200 Video decoding device
201 Code string analyzer
202 Prediction residual decoding unit
203 frame memory
204 motion compensation decoding unit
205 Motion vector storage unit
206 Back picture determination unit
Se sector
Tr Track
FD flexible disk
F Flexible disk case
Cs computer system
FDD flexible disk drive

Claims (21)

A moving image encoding method for encoding a moving image to generate a code sequence,
In the encoding of a B picture in which predictive encoding is performed with reference to a plurality of encoded pictures that are temporally forward or backward, the motion of a current block to be encoded is performed with reference to a motion vector of an encoded block. Including an encoding step that allows to use the direct mode with compensation,
The encoding step, when performing the predictive encoding of the B picture with reference to only the encoded picture in one direction in display order from the picture to which the encoding target block belongs, the encoding is performed as the direct mode. A moving picture coding method comprising a motion compensation step of performing motion compensation by referring to a motion vector of a coded block in the same picture located around a target block. In the motion compensation step, when all the coded pictures referred to for performing the predictive coding are pictures temporally ahead of the picture to which the current block belongs, the motion compensation is performed. 2. The moving picture coding method according to claim 1, wherein the moving picture coding is performed. In the motion compensating step, when there is no coded picture that can be referred to for performing the predictive coding temporally behind the picture to which the current block belongs, the motion compensation is performed. 2. The moving picture coding method according to claim 1, wherein: The motion compensation step includes, in performing the motion compensation, one of a plurality of pictures referred to by a motion vector of the encoded block, in order from a temporally closer to a picture to which the encoding target block belongs. Or refer to a motion vector referring to a plurality of pictures, including a motion vector calculation step of calculating the motion vector of the encoding target block by taking the median or average value thereof,
2. The moving picture coding method according to claim 1, wherein in the motion compensating step, the motion compensation in the direct mode is performed using one or a plurality of motion vectors obtained in the motion vector calculating step. . In the motion vector calculation step, among a plurality of pictures referred to by the motion vector of the coded block, one or more pictures are referred to in a display order closer to a picture to which the coding target block belongs. 5. The moving image encoding method according to claim 4, wherein the motion vector is calculated by referring to the motion vector to be executed. In the motion compensation step, when performing the motion compensation, the position of the encoded block is outside the picture or slice to which the encoding target block belongs, or the motion vector of the encoded block has If the value is “0”, or if the coded block has no motion vector, the value of the motion vector of the current block is set to “0”, and 1 The moving picture coding method according to claim 1, wherein the motion compensation is performed by referring to one or more pictures. A moving image encoding method for encoding a moving image to generate a code sequence,
In the encoding of a B picture in which predictive encoding is performed with reference to a plurality of encoded pictures that are temporally forward or backward, the motion of a current block to be encoded is performed with reference to a motion vector of an encoded block. Including an encoding step that allows to use the direct mode with compensation,
The encoding step includes performing the predictive encoding of the B picture by referring to only the encoded picture in one direction in display order from the picture to which the encoding target block belongs, and performing the encoding as the direct mode. A moving image coding method, wherein a motion vector value of a target block is set to “0”, and motion compensation is performed by referring to one or more pictures in order from a temporally closest one. The encoding step includes excluding the predictive encoding method that refers to the rear from a table in which the predictive encoding method of the B picture and an identifier for identifying the predictive encoding method are associated with each other. Including a table regeneration step for regenerating,
The said encoding step encodes the said identifier which shows the prediction encoding method of the said B picture using the regenerated said table, The Claims 1 to 7 characterized by the above-mentioned. Video encoding method. A moving image decoding method for decoding a code sequence obtained by encoding a moving image,
In decoding a B picture that performs predictive decoding with reference to a plurality of decoded pictures that are temporally forward or backward, the motion of the current block to be decoded is performed with reference to the motion vector of the decoded block. A decoding step allowing to use the direct mode with compensation,
In the decoding step, when performing predictive decoding of the B picture with reference to only a decoded picture in one direction in time from a picture to which the current block belongs, the decoding is performed as the direct mode. A moving picture decoding method, comprising a motion compensation step of performing motion compensation with reference to a motion vector of a decoded block in the same picture located around a target block. In the motion compensation step, when all of the decoded pictures referred to for performing the predictive decoding are only pictures that are temporally ahead of the picture to which the current block belongs, the motion compensation is performed. 10. The moving picture decoding method according to claim 9, wherein In the motion compensation step, when there is no decoded picture which can be referred to for performing the predictive decoding, temporally behind the picture to which the current block belongs, the motion compensation is performed. The moving picture decoding method according to claim 9, wherein: The motion compensation step includes, in performing the motion compensation, one of a plurality of pictures referred to by a motion vector of the decoded block, in order from a temporally closer to a picture to which the current block belongs. Or referring to a motion vector referring to a plurality of pictures, including a motion vector calculation step of calculating the motion vector of the decoding target block by taking the median or average value thereof,
10. The moving picture decoding method according to claim 9, wherein, in the motion compensating step, motion compensation in the direct mode is performed using one or a plurality of motion vectors obtained in the motion vector calculating step. . In the motion vector calculation step, among a plurality of pictures referred to by the motion vector of the decoded block, one or more pictures are referred to in a display order closer to a picture to which the current block belongs. 13. The moving picture decoding method according to claim 12, wherein the motion vector is calculated by referring to a motion vector to be decoded. In the motion compensation step, when performing the motion compensation, if the position of the decoded block is outside the picture or slice to which the decoding target block belongs, or the motion vector of the decoded block has If the value is “0”, or if the decoded block has no motion vector, the value of the motion vector of the block to be decoded is set to “0”, and 1 10. The moving picture decoding method according to claim 9, wherein the motion compensation is performed with reference to one or a plurality of pictures. A moving image decoding method for decoding a code sequence obtained by encoding a moving image,
In decoding a B picture that performs predictive decoding with reference to a plurality of decoded pictures that are temporally forward or backward, the motion of the current block to be decoded is performed with reference to the motion vector of the decoded block. A decoding step allowing to use the direct mode with compensation,
In the decoding step, when performing predictive decoding of the B picture by referring to only decoded pictures in one direction in time from a picture to which the current block belongs, the decoding is performed as the direct mode. A moving picture decoding method characterized in that a motion vector value of a target block is set to "0" and motion compensation is performed by referring to one or more pictures in order from a temporally closest one. The decoding step excludes a predictive decoding method that refers to the backward from a pre-stored table that associates the predictive decoding method of the B picture with an identifier for identifying the predictive decoding method. Including a table regeneration step of regenerating the table,
In the decoding step, an identifier for identifying the predictive decoding method of the B picture is decoded from the encoded sequence, and using the regenerated table, the predictive decoding method of the B picture is identified, The moving picture decoding method according to any one of claims 9 to 15, wherein predictive decoding of the current block is performed according to the identified predictive decoding method. A moving image encoding device that encodes a moving image to generate a code sequence,
In the coding of a B picture in which predictive coding is performed with reference to a plurality of coded pictures located forward or backward in time, the motion of a block to be coded is referred to with reference to a motion vector of a coded block. Comprising an encoding means enabling to use the direct mode with compensation,
The encoding unit, when performing predictive encoding of the B picture by referring only to an encoded picture temporally in one direction from a picture to which the encoding target block belongs, performs the encoding as the direct mode. A moving image encoding apparatus comprising: a motion compensation unit that performs motion compensation by referring to a motion vector of an encoded block in the same picture located around a target block. A moving image decoding apparatus for decoding a code sequence obtained by encoding a moving image,
In decoding a B picture that performs predictive decoding with reference to a plurality of decoded pictures that are temporally forward or backward, the motion of the current block to be decoded is performed with reference to the motion vector of the decoded block. Comprising decoding means allowing to use the direct mode with compensation,
The decoding means, when performing predictive decoding of the B picture with reference to only a decoded picture in one direction in time from a picture to which the decoding target block belongs, performs the decoding as the direct mode. What is claimed is: 1. A video decoding device comprising: a motion compensation unit that performs motion compensation by referring to a motion vector of a decoded block in the same picture located around a target block. A data recording medium storing a program for causing a computer to execute each step of the moving picture encoding method or the moving picture decoding method according to any one of claims 1 to 16. A program for causing a computer to execute each step of the moving picture encoding method or the moving picture decoding method according to any one of claims 1 to 16. An encoded data stream configured by repeatedly arranging a header part and a data part for each slice constituting a picture,
In the direct mode of a B picture in which predictive coding is performed with reference to a plurality of coded pictures that are temporally forward or backward in the header part of each slice, one frame is temporally shifted from the picture to which the current block belongs. When predictive coding is performed with reference to only coded pictures in the direction, motion compensation is performed with reference to motion vectors of a plurality of coded blocks in the same picture located around the current block to be coded. Or a flag indicating that motion compensation is performed with the value of the motion vector of the encoding target block set to “0”,
9. Coded data in which video data encoded by the video encoding method according to any one of claims 1 to 8 is arranged in a data portion of each slice. stream.

Images