Details:
Summary:
It has become commonplace today to apply clear coatings on high-quality printed products. In addition to improving scuff resistance and speeding production throughput time, coatings are also known to improve the dynamic range and, therefore, the visual appearance of the prints. This study examined a number of coated samples produced by PIA/GATF to determine if there were measurable increases in color gamuts associated with the addition of clear coatings. The hypothesis that larger color gamuts would result from the addition of coatings was not supported overall. The attribute of Chroma was used to evaluate whether the gamuts were increasing. It was assumed that overall increases in the Chroma values of color patches from the IT-8 Basic Data Set would indicate larger color gamuts overall. Gloss coatings did tend to show slight increases in Chroma but matte-coated samples tended to have reduced Chroma values and some of the conditions had changes in Chroma that were effectively zero. The discrepancies between measured values and perceived increases of colorfulness might be attributable to the difference between the 45/90 illumination geometry of the spectrophotometer and the non-restricted illumination geometry of the human observer. It was found that the color changes due to coating could be accurately predicted by measuring the color differences of an unprinted sample of the substrate with and without coating applied. The differences in L-, a-, and b-values were used to calculate predicted L-, a-, b-values for all of the color patches. Linear regression showed that the predicted and measured L-, a-, b-values typically had correlation coefficients greater than 0.99. Different combinations of coating, ink, and paper yielded best-fitting lines with slightly different slopes and y-intercepts.