Influence of Luminance vs. Chromaticity Distribution of Surrounding Surfaces on Luminosity Threshold of a Surface Color

Abstract

The luminosity threshold of surface colors depends on luminance of surrounding colors. When there is no or low-luminance surrounding colors a colored light appears as an illuminant, whereas when luminance of surrounding colors are high enough the same colored light appears as a surface (K. Uchikawa, K. Koida, T. Meguro, Y. Yamauchi, & I. Kurik, 2001). It is unclear, however, what statistics of luminance and chromaticity distribution of surrounding colors determine the surface color's luminosity threshold. In this study, we investigated whether differences in luminance vs. chromaticity distribution of surrounding colors influence the luminosity threshold of the test color. In experiments, we used the 15 deg surrounding stimulus consisting of randomly overlapping 2 deg circles with three different distributions of luminance vs. redness; natural surface, uniform and V-shape distribution. The observer adjusted the luminance of the 2 deg circular test stimulus, presented at the center of the display, so that it appeared neither as a complete surface nor a complete illuminant. The results showed that the luminosity threshold changed as a function of redness of the test color, and resembled the luminance vs. redness distribution of natural surfaces in shape. Since the luminance of natural surface colors spreads within the luminance limit of the optimal colors the visual system might recognize the optimal color luminance as the luminosity threshold.