How anisotropy of CIELAB color space affects the separation effect: an experimental study

Almost all modern color difference equations have been developed based on partitioning the value of color difference into the difference of three perceptual color attributes, i.e., hue, chroma, and lightness. Separation of samples, as a parametric effect, has an undeniable impact on the perceived color difference. According to previous studies, there is no meaningful relationship between chromaticity and the separation effect. The present study has been carried out with the aim of investigating the possible relationships between the separation effect and the directions of color difference in CIELAB color space. For this purpose, five color centers were selected. A total number of 44 samples (10 samples around four chromatic color centers and four samples around the gray color center) were prepared employing acrylic water-based painted paperboards. Perceived color difference between each pair against three different backgrounds was assessed through the visual experiments using gray scale method. The results imply that the amount of separation effect depends significantly on the relative position of samples. It is deduced that the separation effect for tritan pairs (two samples in which the difference between them is only due to the response of S cone signals) is lower than deutan pairs (pairs in which the ratio of L cone signals to M cone signals is different for the two samples), which could be attributed to the negligible contribution of S signal difference in producing a naturally occurring border between two abutting samples. Moreover, it is revealed from the outcomes that dark background amplifies the separation effect regardless of color coordinates of the samples.