To provide an image processing technique of compressing borderline information of an image-by-density plane in a multi-valued image and an image processing technique of expanding the compressed information.
The image processing device certifies a bottom borderline LB and its corresponding top borderline LT. Intermediate borderlines LM which are borderlines excluding the bottom borderline LB and the top borderline LT are deleted from a plurality of borderlines having continuous memberships throughout a plurality of density planes from the bottom borderline LB to the top borderline LT. By this, image information is compressed. In expansion, a density value of each picture element within an interpolation process object area between an acquired pair of borderlines (the bottom borderline LB and the top borderline LT) is calculated by an interpolation process based upon respective shortest distances to the top borderline and the bottom borderline and density values of density planes respectively relevant to the bottom borderline and the top borderline.
FUJIMOTO HIROMI
AOKI TERUMASA
OSADA REIKO
YASUDA HIROSHI
