In this study, we further extend the proposed methodology to handle color prints, predicting tristimulus values for prints with multiple and overlapping colorants. After converting the microscopic images of halftone prints into CIEXYZ color space, tristimulus values for the paper and the different combinations of ink are computed from CIEEXYZ histograms. From the microscopic images we can also compute the physical ink area coverage for each of the Neugebauer primaries, which typically differ from the nominal one, due to physical dot gain. The result is an expanded Neugebauer model, taking into account how the tristimulus values of the paper, the primary inks and the overlapping secondary colors, vary with the total ink area coverage. Experimental results confirm the accuracy of the proposed methodology, when compared to measurements using a spectrophotometer. The results have shown that the variation of the micro-reflectance of the Neugebauer primaries is large, and depends on the total ink area coverage. The results further show that the way that the micro-reflectance vary is also strongly dependent on the surrounding inks, because of light scattering in the substrate. |