PURPOSE: To enable the various kinds of processing for compressed image data by synthesizing color images with other image data, compressing the color image data for storing them in a memory, expanding the compressed color image data and using plural color processing means for converting plural image signals for image formation.

CONSTITUTION: The image on an original can be once read by a line sensor having the same width as that of the original provided at the filters of three colors R, G and B. The image read by a CCD 151 is analog/digital converted, converted to digital data by a sample/hold part 152, corrected by a shading correction part 153 and an input masking part 154 and magnified by a magnification processing part 155. These image data are temporarily stored in a compression/expansion part 156, masking processing is performed by a masking/ UCR part 160, output image data are prepared by a γ correction part 161 and an edge emphasis part 162, and these data are supplied through a video processing part 163 to a printer part.