PURPOSE: To increase the total degree of approximation of colors by generating a use color table wherein the reference numbers of the colors are added to plural images the total number of use colors of which possibly exceeds the number of simultaneous display colors when the number of simultaneous display colors is less than the number of colors which can be displayed on a raster type color display device.

CONSTITUTION: A color frequency totalizing device 1 generates frequency statistics of colors used in a raster image, a fixed color table is referred to on a display at this time, and fixed colors are set to a frequency ∞. A color frequency order arraying device 2 arrays the color frequency tables of the image in the decreasing order of frequencies of use and a display color adjusting device 3 adds and rearranges a rearranged color frequency table and the color frequency table on the display. At this time, a new/old color number coordinate table is generated and a color frequency order rearranging device 4 is used for the rearrangement. A color number correcting device 5 generates a display raster image by using the original image and new/old number coordinate table and a color frequency retotalizing device 6 totalizes the frequencies of colors in the display raster image after the color number corrections. A display device 7 displays an image according to a display color table and the display image.