Transition type influences the adaptation state under dichromatic illuminations.

The CATs models proposed over these years (such as CMCCAT97, CAT02 and CAT16) were derived from simple stimuli surrounded by a uniform background with a single illuminant. However, the real scene always consists of more than one illumination, especially in many artificially lit environments. Some previous studies indicate an influence of the transition type between two illuminations on the adaptation state, but the visual data is insufficient to conclude a general trend applicable for any color pair. To systematically investigate how the transition type and illumination color pair interactively influence the adapted white point and degree of adaptation, a series of achromatic matching experiments were conducted under (simultaneously) spatially dichromatic illuminations. Transition type was found to have an impact on the adaptation state, but it is significant only for an illumination pair with a large color difference. In addition, for those sharp-transitioned dichromatic illuminations, the illumination that more easily gets adapted tends to have a higher contribution to the adapted white point than the other one. A more comprehensive CAT model for dichromatic illuminations was derived from the collected visual data.