Colour contrast influences perceived shape in combined shading and texture patterns

Abstract

The 'colour-shading effect' describes the phenomenon whereby a chromatic pattern influences perceived shape-from-shading in a luminance pattern. Specifically, the depth corrugations perceived in sinusoidal luminance gratings can be enhanced by spatially non-aligned, and suppressed by spatially aligned sinusoidal chromatic gratings. Here we examine whether colour contrast can influence perceived shape in patterns that combine shape-from-shading with shape-from-texture. Stimuli consisted of sinusoidal modulations of texture (defined by orientation), luminance and colour. When the texture and luminance modulations were suitably combined, one obtained a vivid impression of a corrugated depth surface. The addition of a colour grating to the texture-luminance combination was found to enhance the impression of depth when out-of-phase with the luminance modulation, and suppress the impression of depth when in-phase with the luminance modulation. The degree of depth enhancement and depth suppression was approximately constant across texture amplitude when measured linearly. In the absence of the luminance grating however, the colour grating had no phase-dependent affect on perceived depth. These results show that colour contrast modulates the contribution of shading to perceived shape in combined shading and texture patterns.

Color improves edge classification in human vision

“…Indeed, while the performance of human observers was improved by size and color, that of classifiers decreases with size, and the difference between color and pure-luminance conditions is less constant. The classifiers we employed used relatively basic properties such as the difference in mean luminance either side of the edge, whereas our human observers were presumably also sensitive to more complex and information-rich color and luminance image properties, such as information about the texture [25–30], shape and spatial orientation of the edge [31–35], as well as higher order contextual information. Indeed, edges rarely occur in isolation, instead in a rich, structured context of other visual information.…”

Texture Variations Suppress Suprathreshold Brightness and Colour Variations

“…In natural scenes luminance decrements and violet contrasts are more present in shadows than are red or texture contrasts [26] , and at least for patterned (vs. rough) textures, texture changes seem only to arise from material changes [11] . If this account is correct then we would predict that abrupt variations in texture orientation – a clear cue to segmentation [41] , [42] – will also dominate over luminance and colour contrast, although the synergy between shading and orientation cues to surface shape [9] , [10] suggests that orientation changes might be less potent in this regard when consistent with a uniform texture on an undulating surface.…”