The invention comprises a device-independent color space converter 241 that obtains device-dependent color signals on the on the color system color coordinates from first color signals, a gradation compensator 242 that determines a black color signal in the second color signals having the identical or virtually identical density as the black color signal in the first color signals, and a YMC decision section 243 that determines the remaining three variable color signals in the second color signals from the black color signal and the device-independent color signals in the second color signals so that calorimetric consistency of the three variable color signals may be obtained.