To make easy a bias of the provability of the occurrence of each plane to exist and to improve a compression rate when a multi-color image is encoded by rearranging indexes of object pixels to be encoded in order of a luminance value.
An index conversion means 3 inputs the color pixel data 1 becoming an original index, and rearranges then in order increasing luminance value, and converts index by imparting a small conversion index 1a to a color with the large luminance value and imparting a large conversion index 1a to the color with the small luminance value. A parallel-serial conversion part input the conversion index 1a to convert it to the serial data 1b, and a first state signal generation means 6 generates a first state signal PBP whenever a converted bit signal is inputted to input it to an occurrence probability generation means 7. An arithmetic operation part 12 user a result of a ROM 11 constituting an entropy encoding means together with the occurrence probability generation means 7 to convert the serial data 1b to the encoding data 2.
TODOROKI MITSUNARI
NINOMIYA NOBORU
