IMAGE DECODER, IMAGE DECODING METHOD, AND IMAGE DECODING PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide an image decoding technique capable of further improving encoding efficiency by reducing a generated code amount of an intra-frame prediction mode.SOLUTION: An image decoder comprises: an intra-frame prediction mode storage unit; a prediction direction difference derivation unit that derives a prediction direction difference indicating a degree of difference between prediction directions of intra-frame prediction modes; a preferential prediction mode list creation unit that creates a list of preferential prediction modes to be candidates for an intra-frame prediction mode of a decoding object block on the basis of the intra-frame prediction modes of a plurality of reference blocks used for derivation of the prediction direction difference and the prediction direction difference; a preferential prediction mode determination flag decoding unit that decodes information indicating whether the intra-frame prediction mode of the decoding object block is a preferential prediction mode; a preferential prediction mode decoding unit that decodes information for identifying the intra-frame prediction mode on the basis of the created list in the case of a preferential prediction mode; and a non-preferential prediction mode decoding unit that decodes the information in the case of a non-preferential prediction mode.