Abstract: The invention is directed to a method and to an apparatus for the calibration of color values in color conversion in apparatus and systems for image processing. Measured color values of an apparatus-dependent input color space are acquired by scanning a suitable test original with a plurality of color fields in an image input apparatus. The measured color values are transformed into color values of an apparatus-independent communication color space in an input color converter on the basis of an analytically approximately calculated conversion table. The approximate calculation of the conversion table occurs taking the pre-distortion of the measured color values and the spectral properties of the respective input apparatus into consideration. The transformed color values are compared to the colorimetrically defined color values of the test originals that are measured, for example, with a spectral photometer.