Video coding method, video decoding method, video coding apparatus and video decoding apparatus

1. A moving picture coding method of merging a prediction direction, a motion vector, and a reference picture index of at least one merging candidate to code a current block, the moving picture coding method comprising:

making a determination as to whether or not to code all blocks in a current picture in a skip mode;

setting, based on a result of the determination, a first flag indicating whether or not a temporally neighboring block which is included in a picture different from the current picture and temporally neighbors the current block is to be referenced;

setting, based on the result of the determination, a value of a parameter for determining a total number of merging candidates;

setting, based on the result of the determination, a second flag for each block included in the current picture, the second flag indicating whether or not each block included in the current picture is to be coded in the skip mode;

determining, based on the first flag and the total number of the merging candidates, the at least one merging candidate from among one or more candidates including a neighboring block which is either a block spatially neighboring the current block in a picture including the current block or a temporally neighboring block included in the picture different from the current picture, the determined at least one merging candidate being at least one candidate usable for the merging;

selecting a merging candidate to be used for coding of the current block from among the determined at least one merging candidate; and

coding an index which indicates the selected merging candidate and attaching the coded index to a bitstream, according to the total number of the merging candidates, wherein

when the determination made in the making of the determination is that all the blocks in the current picture are to be coded in the skip mode, the selected merging candidate is a zero vector candidate, and all the blocks are coded using the zero vector candidate.

2. The moving picture coding method according to claim 1 ,

wherein when the determination made in the making of the determination is that all the blocks in the current picture are to be coded in the skip mode, in the setting of the first flag, the first flag is set to have a value to indicate that the temporally neighboring block is not to be referenced.

3. The moving picture coding method according to claim 1 ,

wherein when the determination made in the making of the determination is that all the blocks in the current picture are to be coded in the skip mode, in the setting of the value of the parameter, the value of the parameter is set to cause the total number of the merging candidates to be determined to be one.

4. The moving picture coding method according to claim 1 ,

wherein when the determination made in the making of the determination is that all the blocks in the current picture are to be coded in the skip mode, in the setting of the second flag, the second flag is set, for each block included in the current picture, to indicate that each block included in the current picture is to be coded in the skip mode.

5. The moving picture coding method according to claim 1 ,

wherein in the making of the determination, a picture skip flag which indicates the result of the determination is attached to the bitstream,

in the setting of the first flag, the first flag is set based on the picture skip flag,

in the setting of the value of the parameter, the value of the parameter is set based on the picture skip flag, and

in the setting of the second flag, the second flag is set for each block included in the current picture based on the picture skip flag.

6. The moving picture coding method according to claim 5 ,

wherein in the setting of the first flag,

when the picture skip flag indicates that all the blocks in the current picture are to be coded in the skip mode, the first flag is set to have a value to indicate that the temporally neighboring block of the current block is not to be referenced, and the first flag is not attached to the bitstream, and

when the picture skip flag indicates that not all the blocks in the current picture are to be coded in the skip mode, the first flag is attached to the bitstream.

7. The moving picture coding method according to claim 5 ,

wherein in the setting of the value of the parameter,

when the picture skip flag indicates that all the blocks in the current picture are to be coded in the skip mode, the value of the parameter is set to cause the total number of the merging candidates to be determined to be one, and the parameter is not attached to the bitstream, and

when the picture skip flag indicates that not all the blocks in the current picture are to be coded in the skip mode, the parameter is attached to the bitstream.

8. The moving picture coding method according to claim 5 ,

wherein in the setting of the second flag,

when the picture skip flag indicates that all the blocks in the current picture are to be coded in the skip mode, the second flag is set, for each block included in the current picture, to indicate that each block included in the current picture is to be coded in the skip mode, and the second flag is not attached to the bitstream, and

when the picture skip flag indicates that not all the blocks in the current picture are to be coded in the skip mode, the second flag set for each block included in the current picture is attached to the bitstream.

9. The moving picture coding method according to claim 1 ,

wherein in the coding of the index, when the total number of the merging candidates is one, the attaching of the coded index which indicates the selected merging candidate to the bitstream is omitted.

10. A moving picture decoding method of merging a prediction direction, a motion vector, and a reference picture index of at least one merging candidate to decode a current block, the moving picture decoding method comprising:

decoding a first flag indicating whether or not a temporally neighboring block which is included in a picture different from the current picture and temporally neighbors the current block is to be referenced;

decoding a value of a parameter for determining a total number of merging candidates;

decoding a second flag which is set for each block included in the current picture and indicates whether or not each block included in the current picture is to be decoded in a skip mode;

determining, based on the first flag and the total number of the merging candidates, the at least one merging candidate from among one or more candidates including a neighboring block which is either a block spatially neighboring the current block in a picture including the current block and or a temporally neighboring block included in the picture different from the current picture, the determined at least one merging candidate being at least one candidate usable for the merging; and

decoding, according to the total number of the merging candidates, an index which indicates a merging candidate to be used for decoding of the current block, the merging candidate to be used for decoding of the current block being among the at least one determined merging candidate, wherein

when each block included in the current picture is to be decoded in the skip mode, the merging candidate to be used for decoding of the current block is a zero vector candidate, and each block included in the current picture is decoded using the zero vector candidate.

11. The moving picture decoding method according to claim 10 , further comprising

decoding a picture skip flag which indicates whether or not all blocks in the current picture are to be decoded in the skip mode,

wherein in the decoding of the first flag, the first flag is decoded based on the picture skip flag,

in the decoding of the value of the parameter, the value of the parameter is decoded based on the picture skip flag,

in the decoding of the second flag, the second flag set for each block included in the current picture is decoded based on the picture skip flag.

12. The moving picture decoding method according to claim 11 ,

wherein in the decoding of the first flag,

when the picture skip flag has a value of one, the decoding of the first flag is omitted.

13. The moving picture decoding method according to claim 11 ,

wherein in the decoding of the value of the parameter,

when the picture skip flag has a value of one, the decoding of the value of the parameter is omitted.

14. The moving picture decoding method according to claim 11 ,

wherein in the decoding of the second flag,

when the picture skip flag has a value of one, the decoding of the second flag is omitted.

15. The moving picture decoding method according to claim 10 ,

wherein in the decoding of the index,

when the total number of the merging candidates is one, the decoding of the index which indicates the merging candidate to be used for decoding of the current block is omitted.

16. A moving picture coding apparatus comprising:

control circuitry; and

storage accessible from the control circuitry,

wherein the moving picture coding apparatus merges a prediction direction, a motion vector, and a reference picture index of at least one merging candidate to code a current block, and

the control circuitry performs the moving picture coding method according to claim 1 .

17. A moving picture decoding apparatus comprising:

control circuitry; and

storage accessible from the control circuitry,

wherein the moving picture decoding apparatus merges a prediction direction, a motion vector, and a reference picture index of at least one merging candidate to decode a current block, and

the control circuitry performs the moving picture decoding method according to claim 10 .

18. The moving picture coding method according to claim 1 ,

wherein the zero vector candidate is a set of a motion vector of a horizontal component of zero and a vertical component of zero and a reference picture index having a value of zero, and

when the determination made in the making of the determination is that all the blocks in the current picture are to be coded in the skip mode, the motion vector in the skip mode is settled to a zero vector using the zero vector candidate.

19. The moving picture decoding method according to claim 10 ,

wherein the zero vector candidate is a set of a motion vector of a horizontal component of zero and a vertical component of zero and a reference picture index having a value of zero, and

when each block included in the current picture is to be decoded in the skip mode, the motion vector in the skip mode is settled to a zero vector using the zero vector candidate.