PURPOSE: To secure the continuity of a color image signal predicted by the color prediction expression of a color image by considering the existence of an ink-plate signal K as for the color prediction method of the color image of a YMCK four-color image processor including an ink plate K.

CONSTITUTION: By the color prediction expression of the color image signal and the color prediction expression of a color output image signal X1Y1Z1, the color image signal is predicted from a color image recording signal YMC and the color output image signal X1Y1Z1 is predicted from the color image signal and the ink-plate signal K. By the color prediction expression of a YMC mixed color image signal X2'Y2'Z2' and the color prediction expression of the color image recording signal YMC, the YMC mixed color image signal X2'Y2'Z2' is predicted from the image signal X1Y1Z1 and the signal K and the color image signal YMC is predicted from the image signal X2'Y2'Z2'. At this time, the color prediction expression of the color image is set so that the image signal X1Y1Z1 and the image signal X2'Y2'Z2' become continuous according to the existence of the signal K.