Patent ID: 8457420

Claim:
An image decoding apparatus which decodes encoded image data encoded by an encoding method configured to designate whether to perform distortion suppression processing of suppressing block distortion before each of two times of frequency conversion, the apparatus comprising: a decoding unit which decodes target encoded image data based on information included in a header of the target encoded image data; a designation unit which designates whether to perform high-speed decoding; an analysis unit which analyzes a header of the target encoded image data and extracts parameter information associated with the distortion suppression processing; and a header information changing unit which rewrites the parameter information in the header with information indicating no execution of the distortion suppression processing and supplies the target encoded image data including the rewritten header to said decoding unit when the parameter information obtained by said analysis unit indicates that the distortion suppression processing has been performed only before first frequency conversion and said designation unit has designated high-speed decoding.