A novel spectral trapping model for color halftones

Abstract

The amount of trapping has a great impact on the gray balance and color reproduction of printed products. The conventional trapping models are print density based and give percentage values to estimate the effect of trapping. In an earlier research, a spectral trapping model was proposed, that defines the trapping effect as the ∆E*_abcolorimetric differences between the real ink overlap (measurements) and the ideal ink overlap. All the trapping models proposed so far, however, only calculate the trapping value for full-tone (solid) ink overlap. As the trapping value for full-tone ink overlap could be overestimating the actual ink trapping effect for halftones, it is important to be able to also approximate the trapping value of color halftones. Furthermore, for a detailed gray balance shift analysis, there is a need to estimate the trapping effect for specific color halftones. In the present paper, we propose a novel spectral trapping model that delivers the trapping value as ∆E*_abcolor difference for color halftones taking into account secondary and tertiary ink overlap. The results of the experiments show that the trapping values for color halftones are much smaller than the corresponding trapping value at full tone. The trapping value of halftones, besides other common quality parameters, should still be considered if some quality inaccuracy, such as gray balance shift, occurs in a print production.