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Byung-Geun Khang, Qasim Zaidi; Illuminant color perception of spectrally filtered spotlights. Journal of Vision 2002;2(7):147. doi: 10.1167/2.7.147.
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© ARVO (1962-2015); The Authors (2016-present)
Color perception in the “illumination” mode always accompanies the perception of object colors. The color perceived to belong to the illumination of the objects is based on clues from the scene within which the objects are perceived instead of being based on any view of the source itself. We have examined the clues on which the color percept of the illumination is based for variegated collections of matte surfaces without highlights. We simulated one of 5 distinct sets of 40 spectrally selective materials (red-blue, blue-green, green-yellow, yellow-red, and balanced) as random ellipses on one half of a CRT screen, and luminance matched achromatic materials on the other half. Equal-energy light filtered through one of 6 Kodak CC30 filters (R, G, B, C, M, Y), or a 0.7 transmittance Neutral Density filter, was simulated as a moving circular spotlight on the chromatic side. Observers matched this light by adjusting the spectrum of a similar moving spotlight on the achromatic side. The backgrounds surrounding the spotlight were presented in 3 conditions: dark, illuminated by the unfiltered equal energy light, and illuminated by dim (20%) equal energy light. Illuminant matches were almost veridical with bright surrounds but not with dim or dark surrounds. The presence of a second illuminant in the scene was thus important for accurate color scission into illuminant and surface colors. When the spotlights were the only illuminants, the chromaticity of the matching spotlight was set near the mean of the spotlighted chromatic region, and set equal to the mean when there was least overlap between illuminant and material spectra. Despite the chromatic information provided when the spotlight traverses materials of diverse spectral reflectance, the perceived chromaticity of the illuminant was close to the mean chromaticity of the scene, as if the visual system assumed that the mean reflectance of the chromatic region was almost a uniform function, i.e. a “near-gray world”.
Grants: NEI EY07556
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