The Effect of Optical Brightening Agent (OBA) in Paper and Illumination Intensity on Perceptibility of Printed Colors

Widely utilized sanctioned color aims for commercial printing are based on paper substrates without optical brightening agents, also known as OBAs. However, in today\u27s market, more and more paper is manufactured with OBAs. This could be problematic for commercial printers as OBAs influence not only paper conformity, but also the accuracy printed colors. This can lead to color mismatch between proofs and the final prints. Recognizing this condition, the objectives of this research were two-fold: first, to verify the perceived color difference between prints due to the presence of OBAs, and second, to study the perceptibility of color differences caused by OBAs in paper substrates, combined with quantitative measurement assessment. In order to satisfy these objectives, the following research questions were investigated: Does CIEDE 2000(∆E00) correlate better with visual scaling or ranking for color differences of printed color pairs than CIELABDE (∆E*ab)? Do different illuminant intensity levels (ISO 3664 P1: 2000lx and P2: 500lx) affect human perceptibility of color differences for color pairs with dark shades? A psychophysical experiment was carried out for evaluating color differences using printed color patches. In total, 27 pairs of printed color patches derived from the IT8.7/4 Target (1,617 color patches) were prepared using the same colorants printed on paper with and without OBA. Each pair was assessed at two levels of illumination by a panel of thirty-four observers. The visual results were used to investigate the relationship between color difference metrics and visual scaling (ranking) of color differences induced by OBAs, as well as the relationship between illumination intensity level and visual scaling of color samples with high-density. The results indicated that: (a) There is better correlation between ∆E00 and the visual scaling of OBA-induced color differences than ∆E*ab; and (b) there is no association between different illumination intensities (i.e., ISO: 3664 P1, P2) and visual scaling of color differences in high-density areas