PURPOSE: To determine an accurate coloring material value by using a scanning densitometer or another photosensitive device, providing a stage to form the first color definition signal set which defines a color on the amount of color components according to a coefficient of conversion and a stage to process the first color definition signal set by a repetitive modification loop.

CONSTITUTION: A photosensitive device in the style of a scanner 10 configurable from a densitometer scans an original picture 12 in a pixel base and forms scanner density output signals indicating the color component of each pixel color. The original picture is formed, e.g. of a combination of the coloring material of a medium such as a transparent screen. The scanner signals can be configurable by a computer and supplied a digital processor 14 forming colorimetric determination signal or data in turn. This data is supplied to an output device or other circuits such as a processing circuit system 16.