Moving picture decoding device, moving picture decoding method, and moving picture decoding program

A moving picture decoding method of decoding a bitstream obtained by coding moving pictures using inter-prediction based on inter-prediction information of a merge candidate in units of blocks obtained by partitioning each picture of the moving pictures, comprising:

• a prediction information decoding step of decoding information indicating a designated number of merge candidates;
• a prediction information deriving step of deriving merge candidates from inter-prediction information of a prediction block neighboring to a decoding target prediction block or a prediction block present at the same position as or near the decoding target prediction block in a decoded picture at a temporally different position from the decoding target prediction block;
• a candidate list constructing step of constructing a merge candidate list from the derived merge candidates;
• a first candidate supplementing step of repeatedly performing a first process for adding to the merge candidate list a merge candidate of which the moving vector has a first value, the inter-prediction mode has a second value and the reference index has a third value;
• a second candidate supplementing step of repeatedly performing a second process for adding to the merge candidate list after the first process a merge candidate of which the motion vector has the first value, the inter-prediction mode has the second value and the reference index has a fourth value until the number of merge candidates included in the merge candidate list after the first process reaches the designated number of merge candidates when the number of merge candidates included in the merge candidate list after the first process is smaller than the designated number of merge candidates;
• and
• a merge candidate selecting step of selecting one merge candidate from the merge candidates included in the merge candidate list of which the number of merge candidates reaches the designated number of merge candidates, wherein:
• the first value is a predefined value that does not differ each time the first process and the second process occur;
• the second value is a predefined value that does not differ each time the first process and the second process occur and indicates that the inter-prediction mode is L0 prediction when a decoding target image is a P picture;
• the third value is a variable that differs each time the first process occurs;
• and
• the fourth value is a predefined value that does not differ each time the second process occurs.

A non-transitory computer-readable recording medium having embodied thereon a moving picture decoding program of decoding a bitstream obtained by coding moving pictures using inter-prediction based on inter-prediction information of a merge candidate in units of blocks obtained by partitioning each picture of the moving pictures, causing a computer to execute:

• a prediction information decoding step of decoding information indicating a designated number of merge candidates;
• a prediction information deriving step of deriving merge candidates from inter-prediction information of a prediction block neighboring to a decoding target prediction block or a prediction block present at the same position as or near the decoding target prediction block in a decoded picture at a temporally different position from the decoding target prediction block;
• a candidate list constructing step of constructing a merge candidate list from the derived merge candidates;
• a first candidate supplementing step of repeatedly performing a first process for adding to the merge candidate list a merge candidate of which the moving vector has a first value, the inter-prediction mode has a second value and the reference index has a third value;
• a second candidate supplementing step of repeatedly performing a second process for adding to the merge candidate list after the first process a merge candidate of which the motion vector has the first value, the inter-prediction mode has the second value and the reference index has a fourth value until the number of merge candidates included in the merge candidate list after the first process reaches the designated number of merge candidates when the number of merge candidates included in the merge candidate list after the first process is smaller than the designated number of merge candidates;
• and
• a merge candidate selecting step of selecting one merge candidate from the merge candidates included in the merge candidate list of which the number of merge candidates reaches the designated number of merge candidates, wherein:
• the first value is a predefined value that does not differ each time the first process and the second process occur;
• the second value is a predefined value that does not differ each time the first process and the second process occur and indicates that the inter-prediction mode is L0 prediction when a decoding target image is a P picture;
• the third value is a variable that differs each time the first process occurs;
• and
• the fourth value is a predefined value that does not differ each time the second process occurs.