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Summary:
This research compared four equations for calculating ink trapping with respect to their correlations with color differences measured by the CIE94 equation. The research questions that this study sought to answer were: * Do changes in trap values correlate with perceptual changes of overprint colors? * Which trap calculation method is the most sensitive to colorimetric changes? The goals were to determine if ink trapping is a useful process control parameter, and, if so, which trapping equation should be used. A press test was conducted at the Graphic Arts Technical Foundation (GATF) where the ink and water settings were systematically varied to induce changes in ink trapping. The results were mixed. There were differences in the correlations for the different two-color overprints and for the different experimental conditions. Also, the trap correlations for the press running at equilibrium were different than the correlations when large color changes were induced. The Ritz formula correlated the best at equilibrium and the Preucil formula correlated best for the larger color changes. Overall, there were strong enough correlations with the color difference values to warrant the measurement of ink trapping for process control, and the Preucil equation performed the best in the critical regions where meaningful color differences were present.