Under specular reflection, non-isotropic halftones such as line halftones printed on an ink-receiving plastic layer superposed with a metallic layer change their colors upon in-plane rotation of the print. This color change is due to the orientation-dependent optical dot gain
of the halftone. A strong dot gain occurs when the incident light is perpendicular to the halftone line structure. A color prediction model is proposed which predicts under specular reflection the color of cyan, magenta and yellow line halftones as a function of the azimuthal rotation angle,
the incident angle and the line frequency. The model is calibrated by measuring 17 reflectances at the (25° : 25°) measurement geometry, with the incident light parallel to the halftone lines. The model has been tested for several azimuthal rotation and incident viewing angles, each
time for 125 different cyan, magenta and yellow ink surface coverages. The obtained prediction accuracies are between ΔE94 = 3.5 and ΔE94 = 7.
A simple color prediction model based on multiple dot gain curves
