IMAGE COMPRESSION APPARATUS, IMAGE COMPRESSION METHOD, IMAGE EXPANDING APPARATUS, AND PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide an efficient image compression apparatus or the like that has scalability with respect to a multi-value image. SOLUTION: A conversion image generating means generates a conversion image with color pallet 8-bits reduced from direct color 24-bits of an original image through conversion. The data quantity of the converted image is reduced to 1/3 of the original image by the color reduction. Then a difference data generating means takes a difference between the converted image and the original image. When the converted image and the original image have a form of disabling the direct difference, after the data form of the converted image is adjusted into the data form of the original image, the difference is taken. Then a compression means applies entropy coding to the difference data to compress the data. Since the converted image is almost similar to the original image, values of the difference data are concentrated around zero. Thus, the difference data compressed by the entropy coding are considerably decreased more than the data quantity of the original image.