Moving picture signal coding method, decoding method, coding apparatus, and decoding apparatus
Moving picture motion compensation coding/decoding predicts a motion vector in a coding block from a motion vector of the adjacent position and codes a differential motion vector calculated from the motion vector to be coded and its prediction motion vector. The coding is performed by switching the coding accuracy between a coding accuracy of the differential motion vector (1) and a coding accuracy of the prediction motion vector and the coding motion vector (2) for each block. Moreover, when decoding the motion vector from the differential motion vector coded by the aforementioned coding, a reversed processing with respect to the coding is performed.
1. A method of decoding an encoded moving picture signal comprising:
dividing the encoded moving picture signal into plural decoding blocks;
calculating a predictive motion vector (PMV) for every decoding block from a decoded motion vector of an adjacent block;
decoding pel accuracy information (mv shift) of a differential motion vector (MVD) of each of the plural decoding blocks, said information indicating a type of pel accuracy previously selected among a plurality of types of pel accuracy for the differential motion vector;
decoding the differential motion vector (MVD) of each of the decoding blocks which was calculated with the type of pel accuracy indicated by the decoded pel accuracy information (mv_shift) of the respective decoding block;
representing a component of the decoded differential motion vector with a type of pel accuracy of the predictive motion vector (PMV) of the respective decoding block; and
calculating a motion information (MV) of the respective decoding block, thereby decoding the encoded moving picture signal and reconstructing the moving picture, using an expression selected from:
MV=(MVD<<mv shift)+PMV,
MV=(MVD<<mv shift)+((PMV>>mv shift)<<mv shift), and
MV=(MVD+(PMV>>mv shift))<<mv shift.
2. The method according to claim 1 , wherein the types of pel accuracy include ⅛-pixel accuracy, ¼-pixel accuracy, ½-pixel accuracy and 1-pixel accuracy.