CMYK pictorial color images, when output to ISO 15339-2 CRPC1~CRPC7 reference printing conditions, are said to have consistent or common color appearance despite their colorimetric differences in white point and gamut volume. However, the concept of consistent color appearance and its enablement through CRPCs have not been experimentally validated. This research, as a part of the CIE TC8-16 on Consistent Color Appearance, explores the effects of gray balance and tone reproduction as underlying criteria of this attribute.
The experiment involves altering the chosen CRPC reference dataset with known colorimetric differences, generating ICC profiles and preparing pictorial color images in the altered printing conditions and conducting psychometric evaluations. In the experiment, we used the CRPC4 dataset as the reference printing condition to print eight CMYK SCID images and their alterations. For each scene, two alterations of gamut volume are created as control datasets resulting in small and large gamut volume conditions that differ from the CRPC4 reference by 4-5 DE00 at the 95th percentile, used as the measure of colorimetric differences between datasets. In addition to the gamut volume alterations, two additional alterations are created by modifying either gray balance or tone reproduction, whereby those alterations differ by 4-5 DE00 at the 95th percentile with the primaries held constant. The research question was formulated as follows: "Will color images with similar colorimetric changes in gamut volume without alterations of GB and TR be perceived as more consistent than similar colorimetric changes due to alterations of GB and TR?" During psychometric evaluations observers were presented two images with gamut alterations as end points. From a pair of images of the same scene randomly chosen among three alternatives: reference CRPC4, GB and TR altered images, they had to select one that yields more consistent color appearance for the entire triplet. In the second experiment, observers were asked to identify one image from the set of three test images: CRPC4 reference, GB and TR altered, to produce the highest color consistency among eight images of different scenes wherein seven of them were produced using CRPC4 reference printing conditions.
The results show that consistent color appearance of images of the same scenes, reproduced in multiple printing conditions, depends on gray balance and tone reproduction. In addition, consistent color appearance of multiple scenes, reproduced in one printing condition, also depends on similar gray balance and tone reproduction.