Color constancy in natural scenes with and without an explicit illuminant cue

Area of Science:

• Vision science
• Color perception
• Psychophysics

Background:

• Humans exhibit remarkable color constancy, maintaining stable surface color judgments under varying illumination.
• This ability is often attributed to the brain's estimation and compensation for illuminant spectral properties.
• However, the precise mechanisms and reliance on explicit illuminant cues remain debated.

Purpose of the Study:

• To investigate whether explicit visual cues of the illuminant are necessary for robust surface color judgments in natural scenes.
• To test the hypothesis that observers estimate illuminant spectral properties to achieve color constancy.

Main Methods:

• Two psychophysical experiments using high-resolution hyperspectral images of natural scenes were conducted.
• Experiment 1: Manipulated sky illuminant color with the sky directly visible.
• Experiment 2: Introduced a gray sphere to provide a direct view of the illumination, then manipulated its color.

Main Results:

• Color constancy varied across image manipulations but showed no reliable effect of illuminant color.
• Surface color judgments remained consistent even when the sky (a primary illuminant cue) was removed from view.
• No significant difference in color constancy was observed when explicit illuminant cues were present versus absent.

Conclusions:

• Explicit visual cues of the illuminant are not essential for achieving color constancy in natural scenes.
• Surface color perception appears to be largely independent of directly estimating or compensating for the illuminant's spectral properties.
• The findings challenge traditional models emphasizing explicit illuminant estimation in color constancy.