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Eli Brenner, Sérgio Nascimento; Surrounding colours influence judgments of surface lightness. Journal of Vision 2012;12(9):952. doi: 10.1167/12.9.952.
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If we were to consider the light reaching our eyes from every surface in isolation, we would be unable to distinguish a white surface under dim illumination from a grey surface under bright illumination. Comparing light reflected by many surfaces helps us to make this distinction. For instance, if a neighbouring surface clearly reflects more light than the surface of interest, the surface of interest cannot be white, because a white surface reflects most of the light that falls on it, so it should be the brightest surface (at least when only considering diffusely reflecting surfaces under uniform illumination). We here examine whether people consider surfaces’ colours within this kind of reasoning. If a neighbouring surface reflects a similar amount of light as the surface of interest, but the light that the neighbouring surface reflects is clearly coloured, the surface of interest is again unlikely to be white, because chromaticity is the result of surfaces reflecting light of different wavelengths to different extents, so the intensity of the illumination must be higher than that of the light from the neighbouring, coloured surface. We presented targets on backgrounds with matched average luminance and chromaticity, and matched variability in luminance and chromaticity, but that differed in whether the brightest parts were coloured or not. A staircase procedure was used to find the luminance at which subjects were equally likely to judge the target to be grey and white. We found that this occurred at a higher luminance when the brightest parts of the scene were coloured. Thus, when judging a surface’s lightness, people consider that the illumination must be brighter than the light from the brightest surface if the brightest surface is coloured.
Meeting abstract presented at VSS 2012
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