Patent ID: 8644382

Claim:
An image decoding device for decoding encoded data so as to form a decoded image, comprising: a decoder configured to decode, from the encoded data, (i) an encode parameter including intra prediction mode information and (ii) prediction residual data, wherein the intra prediction mode information indicates that an intra prediction mode is one of a plurality of intra prediction modes for use in generating a predicted image of the target block to be decoded; an intra prediction mode information obtaining section configured to obtain, from the encode parameter, (i) a flag which indicates whether or not any of a plurality of intra prediction mode candidates related to a target block to be decoded is identical to an intra prediction mode for use in generating a predicted image of the target block to be decoded, (ii) first intra prediction mode selection information which, in a case where the flag indicates that any of the plurality of intra prediction mode candidates is identical to the intra prediction mode for use in generating a predicted image of the target block to be decoded, designates which one of the plurality of intra prediction mode candidates is to be used as a prediction mode for use in generating a predicted image of the target block to be decoded, and (iii) second intra prediction mode selection information which, in a case where the flag indicates that none of the plurality of intra prediction mode candidates is identical to the intra prediction mode for use in generating a predicted image of the target block to be decoded, designates which one of remaining intra prediction modes other than the plurality of intra prediction mode candidates is to be applied to the target block to be decoded; an intra prediction mode selector configured to select, by use of the first intra prediction mode selection information or the second intra prediction mode selection information, an intra prediction mode for use in generating a predicted image of the target block to be decoded; a predictor configured to form, on the basis of the intra prediction mode thus selected, a predicted image of the target block to be decoded; and an adder configured to form a decoded image of the target block to be decoded by adding the predicted image formed by the predictor and the prediction residual data obtained by decoding the encoded data.