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Peter B. Delahunt, David H. Brainard; Comparison of color constancy with respect to illumination changes induced by distinct physical processes. Journal of Vision 2002;2(7):151. doi: 10.1167/2.7.151.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. Distinct physical processes can change the spectrum of the illumination that impinges on a surface. Here we consider two such changes. The first is a change in the spectrum of the light source that provides the scene illumination (light source change). The second is a change in the reflectance of a surface located near a test surface of interest. Such a change in nearby reflectance can affect the spectrum of light reflected onto the test (reflected light change), even when the light source is constant. A color constant visual system must compensate for changes caused by both of these physical processes. We report measurements of constancy with respect to light source and reflected light changes. Methods. Observers viewed synthetic images rendered from three-dimensional scene descriptions and displayed on a CRT-based stereoscope. They made achromatic adjustments to test surfaces embedded in the images. In the light source condition, the test surface received most of its illumination directly from the light source. In the reflected light condition, it received a large fraction of its illumination from light reflected off a neighboring surface. Within each condition, achromatic loci were measured for five different illuminants, and these five illuminants were matched across the two conditions. One illuminant (D65) was chosen as a baseline and the achromatic loci were used to compute a constancy index for illumination changes with respect to this baseline. Results. Constancy was shown for both conditions, but was better for light source changes than for reflected light changes. In both conditions the degree of constancy varied systematically with the color direction of the illuminant change, and the variation was similar in both conditions. This similarity, as well as the results of other experiments in our lab, suggests that the same mechanisms may play a substantial role in mediating constancy for both types of illumination change.
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