Motion vector coding method and motion vector decoding method

Abstract

A motion vector coding unit 117 executes processing including a neighboring block specification step (S100) of specifying a neighboring block which is located in the neighborhood of a current block; a judgment step (Steps S102, S104) of judging whether or not the neighboring block has been coded using a motion vector of another block; a prediction step (S106, S108) of deriving a predictive motion vector of the current block using a motion vector calculated from the motion vector of the other block as a motion vector of the neighboring block; and a coding step (S110) of coding the motion vector of the current block using the predictive motion vector.

The invention claimed is: 
     
       1. A motion vector decoding method for decoding a coded motion vector of a current block in a moving picture, comprising:
 specifying a neighboring block which is located in a neighborhood of the current block and is previously decoded;   deriving a predictive motion vector of the current block; and   decoding the coded motion vector of the current block using the predictive motion vector;   wherein, in the deriving of the predictive motion vector of the current block, when the neighboring block is decoded based on a motion vector of another block, the predictive motion vector of the current block is derived based on the motion vector of the another block.   
     
     
       2. The motion vector decoding method according to  claim 1 , wherein the another block is located temporally at a forward or backward position relatively to the neighboring block. 
     
     
       3. The motion vector decoding method according to  claim 1 , wherein the another block is located in the moving picture including the neighboring block. 
     
     
       4. A motion vector decoding method for decoding a coded motion vector of a current block in a moving picture, comprising:
 specifying three neighboring blocks which are located in a neighborhood of the current block and are previously decoded;   deriving a predictive motion vector of the current block;   decoding the coded motion vector of the current block using the predictive motion vector, wherein a final motion vector of the current block is determined based on the predictive motion vector and a decoded difference motion vector, and   wherein, deriving the predictive motion vector of the current block comprises:
 responsive to determining that at least one of the three neighboring blocks is coded in a skip mode or a direct mode, deriving the predictive motion vector of the current block based on a motion vector of another block different from the three neighboring blocks, and 
 responsive to determining that none of the three neighboring blocks are coded in the skip mode or the direct mode, deriving the predictive motion vector of the current block based on one or more motion vectors of the three neighboring blocks.