Method for computer-aided performance of transformations of color data from a source color space to a target color space using a given transformation rule TRV,
- wherein the source color space comprises n colors which are present in combinations of color portions q(1) to q(n) in each dot to be printed,
- the target color space comprises m values that can be combined to form combinations of components z(1) to z(m),
- and there are at least some combinations of color components q(1), q(2), . . . , q(n) of the source color space for which combinations of components z(1), z(2), . . . , z(m) of the target color space are assigned,
- characterized by the following steps:
- a) selecting a set of color data Q1 of the n colors of the source color space with the color components q(1), q(2), . . . , q(n), for which a target value data set Z1 is available in the form of combinations of components z(1), z(2), . . . , z(m) of the target color space;
- b) generate a second set of color data Q2 of the n colors of the source color space with the color components q′(1), q′(2), . . . , q′(n), which are initially set identical to Q1;
- c) transform the second set of color data Q2 using the transformation rule TRV to generate an actual value data set Z2 of the m values of the target color space z′(1), z′(2), . . . , z′(m);
- d) applying an n-dimensional optimization procedure which, by suitably modifying the second set of color data Q2 and by repeating step c), minimizes the differences between the nominal value data set Z1 and the actual value data set Z2 in the sense of least squares error, so that Q2 finally contains the resulting optimized color components q′(1), q′(2), . . . , q′(n);
- e) calculating the differences Dq(1)=q′(1)−q(1), Dq(2)=q′(2)−q(2), . . . , Dq(n)=q′(n)−q(n) of each color portion of the n colors of the optimized color data second set Q2 to the respective color portion of the color data set Q1;
- f) calculating the differences Dz(1)=z(1)−z′(1), Dz(2)=z(2)−z′(2), . . . , Dz(m)=z(m)−z′(m) of each component of the color data set Z1 to the respective component of the color actual value data set Z2;
- g) applying the differences Dq(1), Dq(2), . . . , Dq(n) and Dz(1), Dz(2), . . . , Dz(m) in transformations of sets of color data from the source color space with n colors into the m values of the target color space, by adding the difference Dq(i) to the color data q(i) of the n colors of the source color space for the i=1 to n values when transforming a data set, the color data q′(i) modified in this way are transformed with the aid of the transformation rule TRV into the m components z′j) for the j=1 to m values of the target color space, and then the corresponding difference Dz(j) is added to the respective component z′(j),
- wherein the method is carried out for a plurality of sets of color data Q and in that the determined differences Dq(i)3 and Dz(i)3 for a plurality of sets Q are managed in transformation tables and, in the case of transformations in step f), the differences to be applied are interpolated in these transformation tables, and
- wherein the method requires,
- a first correction, wherein said first correction corrects data relating to the corners of the CMYK color space, and utilizing differences from the source color space, target color space of the CMYK color space used in the first correction and the transformation rule TRV to generate a corner-corrected transformation TRV1,
- a second correction, wherein said second correction provides CMYK print data that is accurate at all corners and in the midtones and is output in a state that could receive minor adjustments, utilizing the differences of source color space and target color space of CMYK print data used in the second correction with the transformation TRV1 to generate a further corrected model TRV2, and
- spectrally simulating and then displaying on a screen CMYK print data based on the corrections to model TRV2.