Process for the determination of colorimetric differences between two

Abstract

In a process for the evaluation of the quality of prints and for the color control or ink regulation of a printing machine, half tone fields, preferably gray balance fields, are scanned by a densitometer. The half tone density differences obtained by comparative measurements are transformed by an experimentally determined transform matrix into colorimetric measure differences of a color space uniformly graduated relative to perception, so that on the one hand the advantages resulting from quality evaluations in a true colorimetric system instead of a densitometric measure system may be utilized, and on the other, the use of regulation strategies requiring a colorimetric measuring system, such as for example the L*a*b* system or the LUV system, becomes possible. The transform matrix system is determined experimentally by producing a reference calibrating print and several addition calibrating prints, each containing one gray balance field and three full tone fields. In the case of each addition calibrating print the layer thickness of another full tone field is increased. By detecting the colorimetric measure differences and the half tone density differences and substituting them into a system of equations expressing the relationship between the half tone density differences and the colorimetric measure differences, the elements of the transform matrix describing the relationship between the half tone density variations and the associated colorimetric variations, may be determined.