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 a moving picture using a motion vector in units of blocks obtained by partitioning each picture, comprising:

• a decoding step of decoding information representing a motion vector predictor index to be selected in a motion vector predictor candidate list;
• a motion vector predictor candidate constructing step of deriving first and second motion vector predictor candidates from a motion vector of one of decoded blocks neighboring a decoding target block in a same picture as the decoding target block, and deriving a third motion vector predictor candidate from a motion vector of one of blocks of a decoded picture different from the decoding target block;
• a motion vector predictor candidate adding step of adding the first to third motion vector predictor candidates satisfying a certain condition to a motion vector predictor candidate list;
• a redundant motion vector predictor candidate determining step of deleting the second motion vector predictor candidate from the motion vector predictor candidate list when the first and second motion vector predictor candidates added to the motion vector predictor candidate list by the motion vector predictor candidate adding step have the same values;
• a motion vector predictor candidate limiting step of repeatedly adding a motion vector predictor candidate having a same value to the motion vector predictor candidate list until the number of motion vector predictor candidates reaches a certain number when the number of the motion vector predictor candidates added to the motion vector predictor candidate list is smaller than the certain number (a natural number larger than or equal to 2);
• and
• a motion vector predictor selecting step of selecting a motion vector predictor of the decoding target block from the motion vector predictor candidate list based on the decoded information representing the motion vector predictor index to be selected, wherein the redundant motion vector predictor candidate determining step does not compare the value of the first motion vector predictor candidate and the value of the second motion vector predictor candidate with the third motion vector predictor candidate.

A non-transitory computer-readable recording medium storing a moving picture decoding program of decoding a bitstream obtained by coding a moving picture using a motion vector in units of blocks obtained by partitioning each picture, the moving picture decoding program causing a computer to execute:

• a decoding step of decoding information representing a motion vector predictor index to be selected in a motion vector predictor candidate list;
• a motion vector predictor candidate constructing step of deriving first and second motion vector predictor candidates from a motion vector of one of decoded blocks neighboring a decoding target block in a same picture as the decoding target block, and deriving a third motion vector predictor candidate from a motion vector of one of blocks of a decoded picture different from the decoding target block;
• a motion vector predictor candidate adding step of adding the first to third motion vector predictor candidates satisfying a certain condition to a motion vector predictor candidate list;
• a redundant motion vector predictor candidate determining step of deleting the second motion vector predictor candidate from the motion vector predictor candidate list when the first and second motion vector predictor candidates added to the motion vector predictor candidate list by the motion vector predictor candidate adding step have the same values;
• a motion vector predictor candidate limiting step of repeatedly adding a motion vector predictor candidate having a same value to the motion vector predictor candidate list until the number of motion vector predictor candidates reaches a certain number when the number of the motion vector predictor candidates added to the motion vector predictor candidate list is smaller than the certain number (a natural number larger than or equal to 2);
• and
• a motion vector predictor selecting step of selecting a motion vector predictor of the decoding target block from the motion vector predictor candidate list based on the decoded information representing the motion vector predictor index to be selected, wherein the redundant motion vector predictor candidate determining step does not compare the value of the first motion vector predictor candidate and the value of the second motion vector predictor candidate with the third motion vector predictor candidate.