PICTURE DATA COMPRESSION METHOD

摘要

PURPOSE:To suppress picture quality deterioration in a decoded picture and to reduce data quantity to be saved without need of plural stages of arithmetic operation taking a difference between an original picture and an expanded picture over the entire picture area. CONSTITUTION:Original picture data Do are compressed to obtain compressed picture data Dc, the compressed picture data Dc are expanded to obtain 0-th expanded picture data Dr0. Then a 1st low picture quality area is extracted based on the original picture data Do and the 0-th expanded picture data Dr0, a difference between the original picture data Do and the 0-th expanded picture data Dr0 is compressed within the low picture quality area to obtain a 1st compression differential data Dd1. Furthermore, expansion differential data obtained by expanding the 1st compression differential data Dd1 and the 0-th expanded picture data Dr0 are added to obtain 1st expanded picture data Dr1. Thus, the processing to obtain the compressed differential data in which the picture of a low picture quality area reaches a prescribed picture quality rank or over is repeated in this way.