IMAGE ENCODER, IMAGE ENCODING METHOD, AND IMAGE ENCODING PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide an image encoding technique capable of further improving encoding efficiency by reducing a generated code amount of an intra-frame prediction mode.SOLUTION: A prediction direction difference calculation unit 604 calculates a prediction direction difference between intra-frame prediction modes of a plurality of reference blocks used for intra-frame prediction of an encoding object block. A preferential mode determination unit 603 determines a preferential prediction mode of the encoding object block on the basis of the intra-frame prediction modes of the plurality of reference blocks used for calculating the prediction direction difference and the prediction direction difference. An encoding tree selection unit 605 selects one encoding tree in which a code sequence having a code length shorter than those of other prediction modes is allocated to the preferential prediction mode according to the calculated prediction direction difference from among a plurality of encoding trees prepared according to prediction direction differences in order to encode an intra-frame prediction mode of the encoding object block. A variable-length encoding unit 606 encodes the intra-frame prediction mode of the encoding object block in accordance with the selected encoding tree.