Patent ID: 8165217

Claim:
An image data decoding method for decoding compression encoded image data including a plurality of image pictures, wherein each of the plurality of image pictures is divided into a plurality of blocks each having a predetermined number of pixels, and each of the plurality of image pictures is able to refer to respective reference pictures for each block, comprising: a selection step of selecting, when one of the plurality of image pictures is to be decoded, and when a first reference picture to be referred to by each block included in the one image picture to be decoded is not decoded, a second reference picture from a picture already decoded as an alternative reference for each block of the one image picture to be decoded; and a decoding step of decoding each block included in the one image picture to be decoded with reference to the second reference picture as an alternative to the first reference picture, wherein the selecting in said selection step and the decoding in said decoding step are executed when the plurality of image pictures is being decoded at a predetermined interval.