Human color constancy in cast shadows.

Illumination conditions inside and outside cast shadows typically differ significantly in both intensity and in chromaticity. However, our daily experiences suggest that we generally have no difficulty in stably perceiving surface color in cast shadows. In this study, two experiments were conducted to measure the extent to which color constancy holds within cast shadows. We constructed a scene with colored hexagons illuminated by two projectors simulating "sunlight" and "skylight." Part of the scene included a cast shadow, illuminated only by the skylight, where a subjective white point was measured. We also created a condition in which a cast shadow was not perceived as a shadow. Results showed that color constancy generally holds well in shadows, and the color of skylight had varying effects depending on observers. Perceiving a cast shadow as a shadow had no effect. Overall, these findings are consistent with our daily experiences, in which we stably judge objects' color even within cast shadows.