1. A image processing system, comprising: an image input unit; a hue determining unit to determine hue of an image; a color matching processing unit that converts RGB signals of the input image determined by the hue determining unit into CMYK signals; a γ correction processing unit that corrects gradation characteristics of the input image data; a selecting unit to select halftone processing in accordance with the determined hue; a halftone processing unit to convert the image into an image having a different granularity degree from that of the input image by subjecting the input image data to the selected halftone processing; and an image output unit, wherein the image is simulated with the same gradation characteristic regardless of the selected halftone processing.