Natsumi Tsuji¹, Tama Kanematsu², Kowa Koida¹; ¹Toyohashi university of technology, ²Kyushu University

Color assimilation is a perceptual phenomenon where the color appearance of the center region assimilates to the surrounding area. This phenomenon is driven by both optical and neural factors. The optical factors involve the smoothing of the retinal image due to chromatic aberration and light scattering, while the neural factors refer to the spatial summation during post-receptoral processing. While these factors are summed, the relative contributions of each to color assimilation remain unclear. To investigate this, we conducted a psychophysical experiment and optical simulation of the eye. In the psychophysical experiment, we measured the effects of inducer hue and background luminance on color assimilation using stimuli imitating a watercolor effect. Observers viewed illusions with varying background luminance and reported whether color assimilation was perceived. Color assimilation typically occurred when the luminance contrast between the inducer and background was low, although significant hue dependency was observed. Specifically, a relatively high luminance background was preferred for red inducers, while a low luminance background was preferred for blue inducers. Additionally, red inducers often elicited no color assimilation responses. The optical simulation, based on the spectral optical transfer function, was performed on the same images used in the psychophysical experiment. The resulting retinal images were analyzed for luminance contrast between the inducer and the center region. We found that retinal images with the lowest luminance contrast varied depending on the hue of the inducer. This hue dependency was consistent with the psychophysical results, suggesting that the hue and luminance dependencies of color assimilation could be attributed to optical aberrations.