Does human color constancy incorporate the statistical regularity of natural daylight?

Abstract

The chromaticities of natural daylights cluster around the blackbody locus. We investigated whether the mechanisms that mediate human color constancy embody this statistical regularity of the natural environment, so that constancy is best when the illuminant change is one likely to occur. Observers viewed scenes displayed on a CRT-based stereoscope and adjusted a test patch embedded in the scene until it appeared achromatic. Scenes were rendered using physics-based graphics software (RADIANCE) coupled with custom extensions that ensured colorimetric accuracy. Across conditions, both the simulated illuminant and the simulated reflectance of scene objects were varied. Achromatic settings from paired conditions were used to compute a constancy index (CI) that characterizes the stability of object appearance across the two illuminants of the pair. Constancy indices were measured for four illuminant changes from a Neutral illuminant (CIE D65). Two of these changes (Blue and Yellow) were consistent with the statistics of daylight, whereas two (Green and Red) were not. The results indicate that constancy was least across the Red change, as one would expect for the statistics of natural daylight. Constancy for the Green direction, however, exceeded that for the Yellow illuminant change and was comparable to that for the Blue. This result is difficult to reconcile with the hypothesis that mechanisms of human constancy incorporate the statistics of daylights. Some possible reasons for the discrepancy are discussed.

How Reliable is Perception?

“…Learning that an especially delicious berry has a particular color as observed at noon, would be all the more useful if the knowledge could be generalized to seeing the berry at twilight. Color constancy mechanisms-partly evolved, partly learned (Delahunt & Brainard, 2004;Granzier & Gegenfurtner, 2012)-are a solution to this problem. But that we perceive something as 'red' across a range of contexts does not mean that there is some invariantly "red" thing out there.…”

Perceptual analysis of distance measures for color constancy algorithms

“…The first is the color constancy index CCI [26], also called the Brunswik ratio [27], and is generally used to measure perceptual color constancy [28,29]. It is defined as the ratio of the amount of adaptation that is obtained by a human observer versus no adaptation at all:…”

Effects of chromatic image statistics on illumination induced color differences

“…Also, from a small experiment using the scenes in Fig. 5 of [21], presented as images in our experimental paradigm, the results for 3 observers indicate a strong preference for yellow and blue (83% of the visual score) over red and green (17%). These findings shed some new light on the issue and seem worthwhile to further investigate.…”

“…In line with previous studies [21,22] we select a neutral reference illuminant (D65) and four chromatic illuminants, all composed with the CIE basis functions for spectral variations in natural daylight. In [21] it is investigated whether color constancy would be better for illuminant changes along the daylight locus than for illuminant changes perpendicular to it, but no experimental evidence was found that unambiguously supports this hypothesis.…”

“…In [21] it is investigated whether color constancy would be better for illuminant changes along the daylight locus than for illuminant changes perpendicular to it, but no experimental evidence was found that unambiguously supports this hypothesis. Here, we use the same paradigm with the yellow and blue illuminants along the daylight locus, and another two (red and green) perpendicular to it, but without the constraint that they are perceptually equidistant from the neutral reference point.…”