Determining visually achromatic colours on substrates with varying chromaticity

摘要

Visually neutral colours on three different graphic arts substrates were chosen in a psychophysical experiment. Observers selected the most neutral patch from 49 patches of similar lightness, where the substrate was allowed to provide an adapting field. The results showed that the colours seen as visually neutral tend to have CIELAB a~*, b~* coordinates of 0 at the black point and to approach the a~*, b~* coordinates of the substrate at higher lightnesses. The adaptation to the substrate could be considered complete for a white substrate, but incomplete in non-white substrates. The results were modelled by transforming the achromatic axis in CIELAB by two methods - one by normalizing to the XYZ of the paper white, and the other by the chromatic adaptation transform CMCCAT2000. The best results were obtained when the adopted white point was taken as the substrate XYZ, with the chroma scaled by a factor of 0.6. Chroma scaling had more impact on the results for normalization than for CMCCAT2000.