Motion vector coding method and motion vector decoding method

摘要

The present invention improves efficiency of coding motion vectors when a current block is coded using a plurality of motion vectors. A motion vector coding unit (117) codes a motion vector inputted from a motion vector detecting unit (108). A motion vector for each current block is coded based on a difference between the motion vector and a predicted vector obtained from motion vectors for previously coded neighboring blocks. The predicted vector is generated by one of the following processing: (A) the motion vectors which refer to the same picture are selected from among the motion vectors for the neighboring blocks so as to generate the predicted vector; (B) the motion vectors for the respective neighboring blocks are ordered in the predetermined order, and the motion vectors of the same order rank are selected from the ordered motion vectors so as to generate the predicted vector; and (C) the predicted vector for the second motion vector of the current block shall be the first motion vector, and if the second motion vector and the first motion vector refer to different pictures, the first motion vector is scaled according to the temporal distance between the pictures so as to generate the predicted vector.