Determinants of Colour Constancy and the Blue Bias

Abstract

We investigated several sensory and cognitive determinants of colour constancy across 40 illumination hues. In the first experiment, we measured colour naming for the illumination and for the colour induced by the illumination on the colorimetric grey. Results confirmed that the induced colours are approximately complementary to the colour of the illumination. In the second experiment, we measured colour constancy using achromatic adjustments. Average colour constancy was perfect under the blue daylight illumination and decreased in colour directions away from the blue daylight illumination due to undershooting and a strong blue bias. Apart from this blue bias, colour constancy was not related to illumination discrimination and to chromatic detection measured previously with the same setup and stimuli. We also observed a strong negative relationship between the degree of colour constancy and the consensus of naming the illumination colour. Constancy coincided with a low naming consensus, in particular because bluish illumination colours were sometimes seen as achromatic. Blue bias and category consensus alone explained >68%, and all determinants together explained >94% of the variance of achromatic adjustments. These findings suggest that colour constancy is optimised for blue daylight.

The time course of chromatic adaptation under immersive illumination

“…The extent of chromatic adaptation is known to depend on multiple factors: duration of adaptation [15][16][17][18], spatial and chromatic characteristics of the surround [19,20], chromaticity and intensity of adapting light [21,22], and intensity of the test stimulus [23]. Correspondingly, the extent of colour constancy as measured by the perceptual whitepoint also depends on these factors, and therefore differences in colour constancy indices reported from achromatic adjustment studies may also be due to variations in these factors [9,22,24]. In particular, reported differences in the chromatic bias of achromatic points and their dependence on the chromaticity or intensity of the adapting light [9,21,22] may be partly explained by crucial differences in adaptation duration and surround conditions, as well as by differences in viewing conditions.…”

“…Correspondingly, the extent of colour constancy as measured by the perceptual whitepoint also depends on these factors, and therefore differences in colour constancy indices reported from achromatic adjustment studies may also be due to variations in these factors [9,22,24]. In particular, reported differences in the chromatic bias of achromatic points and their dependence on the chromaticity or intensity of the adapting light [9,21,22] may be partly explained by crucial differences in adaptation duration and surround conditions, as well as by differences in viewing conditions. Studies agree that chromatic adaptation occurs on distinct time scales, from seconds and minutes ("short-term") to hours and days ("long-" and "very-long-term") [18], supporting the hypothesis that multi-level neural mechanisms contribute to adaptation.…”

“…A high level of adaptation completeness is observed, with similar levels of completeness for all illumination hues. In contrast, Weiss et al (2017) [22] test chromatic adaptation to an on-screen surround for 40 simulated illumination hues, using untimed achromatic adjustment in a patch-surround setup, and report almost all achromatic adjustments being shifted towards blue. Lee et al (2012) [25] measure the shift in the achromatic point with changing illumination via the intersection of blue-yellow and red-green judgements for 120 surfaces, for two illuminations, sunlight (yellow) and skylight (blue), and a timecourse of 21 seconds.…”

“…The size and content of the adapting field are therefore important factors, and these differ significantly between studies, from fully isolated small-field stimuli in Maxwellian view [21] to midsize-field computer monitor displays (e.g. ∼ 60 • by 40 • [16,22]; ∼ 38 • by 30 • [25]), to fully immersive illumination environments [9,23].…”

“…the gamut expansion effect, [26]) being maximal for minimal contrast, and strongly reduced by the insertion of black borders between stimulus and surround [26,27]. These effects, though, are confounded by the potential of the surround to supply a neutral reference surface from which the illumination chromaticity may simply be inferred [24]; the stimulus configuration of Weiss et al (2017), for example, includes both local and global backgrounds of neutral surface reflectance (uniform and luminance-noise, respectively), while Brainard's (1998) configuration includes several neutral surface of differing luminances.…”