Contribution of a luminance-dependent S-cone mechanism to non-assimilative color spreading in the watercolor configuration

Abstract

In the watercolor configuration composed of wavy double contours, both assimilative and non-assimilative color spreading have been demonstrated depending on the luminance conditions of the inner and outer contours (IC and OC, respectively). This study investigated how the induced color in the watercolor configuration was modulated by combinations of the IC and the OC color, particularly addressing non-assimilative color spreading. In two experiments, the IC color was fixed to a certain color and combined with various colors selected from a hue circle centered at the background white color. Color spreading was quantified with a chromatic cancelation technique. Results showed that both the magnitude and the apparent hue of the color spreading were largely changed with the luminance condition. When the IC contrast (Weber contrast of the IC to the background luminance) was smaller in size than the OC contrast (higher IC luminance condition), the color spreading was assimilative. When the luminance condition was reversed and the IC contrast was greater than the OC contrast (lower IC luminance condition), the color spreading was non-assimilative and yellowish. When the color spreading was analyzed in terms of cone-opponent excitations, the results were consistent with the interpretation that the color spreading is explainable by a combination of chromatic diffusion from the IC and chromatically opponent induction from the OC. The color spreading in the higher IC luminance condition mainly reflected the chromatic diffusion by both (L–M) and S cone-opponent mechanisms. The non-assimilative color spreading in the lower IC luminance condition mostly reflected S-cone mediated opponent induction and the contribution of −S inducing mechanisms was differentially large. These findings provided several constraints on possible visual mechanisms underlying the watercolor effect.

A Compound Computational Model for Filling-In Processes Triggered by Edges: Watercolor Illusions

“…This maximum response represents the dominant gradient in the image, which is used by the model to determine the strongest effect on the diffusion process. This determination of the strongest effect (i.e., the strongest edge in the stimulus) is in agreement with previously reported psychophysical findings (Pinna et al, 2001; Devinck et al, 2005, 2006; Kimura and Kuroki, 2014a,b). The multiplication operation of the chosen weight is done with a 2D Gabor filter, Equation (5).…”

“…(D) The visual system uses separated chromatic opponent channels [L/M, (L+M)/S and achromatic], in order to process each contrast color pathway separately (Kandel et al, 2012). This assumption is in agreement with experimental studies which claimed that the (L/M) and S-cones are regulated differently with respect to the watercolor effect (Devinck et al, 2005; Kimura and Kuroki, 2014a,b). (E) The chromatic channels are mediated by the Luminance channel (the achromatic channel).…”

“…The first part presents the model predictions for the assimilative (classic) watercolor effect. The second part presents the predictions of the model for the non-assimilative (non-classic) watercolor effect, while the third part presents the model predictions that relate to additional properties of the watercolor effect: the influence of the background luminance, and the effect of the inner color luminance on the perceived hue and the perceived brightness (Devinck et al, 2005, 2006; Cao et al, 2011; Kimura and Kuroki, 2014a,b).…”

“…In order to compare the predictions of the model to psychophysical findings we created sets of images that contain the same color values that have been used in previous psychophysical experiments (Devinck et al, 2005; Kimura and Kuroki, 2014b). Each color value used in the stimulus was converted from the CIE Lu'v' 1976 color space to the sRGB color space, in order to create the input images for the model.…”

“…In order to produce the chromatic (or the achromatic) diffusion process, the visual system needs to enhance or change the original gradients in order to obtain an image which creates the perception and avoids a return to the original image. Based on psychophysical findings, the model assumes that the chromatic edges, which determine the filling-in effect, are significantly influenced by the intensity and by the chromaticity of the contours (IC and OC) (Pinna et al, 2001; Devinck et al, 2005, 2006; Pinna and Grossberg, 2005; Pinna and Reeves, 2006; Cao et al, 2011; Hazenberg and van Lier, 2013; Coia and Crognale, 2014; Kimura and Kuroki, 2014a,b).…”