Motion vector coding method and motion vector decoding method

A moving picture decoding apparatus for decoding a current picture using a motion vector of a current block, comprising:

• a non-transitory memory storing a program;
• and
• a hardware processor that executes the program and causes the moving picture decoding apparatus to operate as:
• a neighboring block specify unit that specifies a plurality of neighboring blocks which are located in a neighborhood of the current block and are previously decoded;
• a different motion vector determining unit that determines a different motion vector of the neighboring block;
• a predictive motion vector deriving unit that derives a predictive motion vector of the current block using the different motion vector of the neighboring block;
• a recovered motion vector generating unit that generates a recovered motion vector of the current block using the predictive motion vector;
• a motion compensation unit that generates a motion compensated picture using the recovered motion vector and a reference picture corresponding to the recovered motion vector of the current block;
• a moving picture decoding unit that decodes a prediction error between the current block and the motion compensated picture;
• and
• a picture recovering unit that obtains a recovered picture of the current block by adding the motion compensated picture and the decoded prediction error,
• wherein, the predictive motion vector of the current block the predictive motion vector of the current block is a calculated median of different motion vectors of the plurality of neighboring blocks, and
• a judging unit that judges if each of the plurality of neighboring blocks does not have a coded motion vector in a bit stream and is motion compensated in spatial direct mode using a motion vector of another block included in the current picture, and
• when the judging unit judges that the neighboring block does not have the coded motion vector in the bit stream and is motion compensated in the spatial direct mode using a motion vector calculated from a motion vector of the other block, a calculated median of motion vectors of the other block is determined to be the different motion vector of the neighboring block by the different motion vector determining unit, and
• when the judging unit judges that the neighboring block has the coded motion vector in the bit stream and is motion compensated using the motion vector of the neighboring block, which is detected in a coding process of the neighboring block and which is used in a motion compensation of the neighboring block, the detected motion vector of the neighboring block is determined to be the different motion vector of the neighboring block by the different motion vector determining unit, and
• the current block, the neighboring block, and the other block are included in the current picture.