IMAGE DECODER AND IMAGE DECODING METHOD

摘要

PROBLEM TO BE SOLVED: To obtain an MPEG down-decoder where a phase deviation of a pixel between a field DCT mode and a frame DCT mode is eliminated without losing interlace performance of an interlace scanning image. SOLUTION: A reduction inverse discrete cosine transform device 14 executes 4×4 reduction IDCT to MPEG data when a DCT mode is in a field mode. A reduction inverse discrete cosine transform device 15 executes IDCT to all coefficients of a DCT block when the DCT mode is in a frame mode to separate the block into two pixel blocks corresponding to interlace scanning, and it executes DCT to the two separated pixel blocks respectively. Then IDCT is executed for low frequency coefficients of the two pixel blocks to composite the two pixel blocks.