In the above processing, the values of X, Xf, and Xb relating to the first calibration point P91 (see FIG. 22) are obtained by colorimetry of the patches PA91, PA92, and PA93 in the spot color 2 chart. However, if a highly accurate overprint prediction value is not necessary, the first calibration point P91 can be regarded as being located at the origin of the graph in FIG. 22 for simplicity. In this case, the colorimetry of the patches PA91 and PA93 in the spot color 2 chart is not necessary (the colorimetry of the patch PA92 is still necessary for obtaining the values of X and Xf of the second calibration point P92). In this case, the tristimulus values X, Y, and Z as the overprint prediction values can be calculated without printing the lower patch group including the patches PA91 and PA93 in the C×F chart shown in FIG. 20. The C×F chart having the upper patch group shown in FIG. 20 without having the lower patch group is herein referred to as a “simple C×F chart” for convenience.
As described above, according to the Deshpande et al. method, color prediction is performed using a C×F chart, for example, as shown in FIG. 20. However, even when printing using spot colors is performed, such a C×F chart is usually not printed in advance. For this reason, it is necessary to print the same number of C×F charts as the same number of the spot colors and perform colorimetry of the respective patches. This causes an increase in cost and man-hours.
