Perceptual luminosity threshold on the surround stimulus that simulates luminance-chromaticity distributions in natural scene
53.448, Tuesday, May 14, 8:30 am - 12:30 pm, Orchid Ballroom
Kazuho Fukuda1, Ai Numata1, Keiji Uchikawa1; 1Department of Information Processing, Tokyo Institute of Technology
Perceptual luminosity threshold depends on the chromaticity and luminance of surround colors. It is unclear, however, how luminosity threshold is determined by surrounding colors. Theoretically the luminance-chromaticity distribution of surface colors cannot exceed MacAdam's limit; the theoretical maximum gamut of object colors under given illumination. We previously showed that the luminosity threshold function maintains the stable shape resembling MacAdam's limit regardless of surround colors luminance-chromaticity distribution and hypothesized that the visual system applies this theoretical or empirical limitation to judge luminosity threshold. To investigate this hypothesis, this study measured luminosity threshold function with regard to several conditions of surrounding colors that simulated the luminance-chromaticity distribution in natural scenes. The stimulus consists of a circular test region and surround overlapping colored circles. There were nine conditions of surround color's luminance-chromaticity distributions simulating LMS cone responses evoked by natural objects spectral reflectance (Brown, 2003) under the black body radiation at 3000, 6500 or 20000K. In this simulation, 180 of Brown's 574 spectral reflection data were selected to create the following three different shapes of luminance-redness distribution under equal energy white illumination; (1) normal shape where the luminance decreases as the redness deviates from achromatic point, (2) V-shape where the luminance increases as the redness deviates from achromatic point, (3) flat shape where the luminance is constant across the redness axis. Observers were instructed to adjust the luminance of test region to perceptual luminosity threshold. The results showed that the luminosity threshold function maintained the constant shape for all conditions as our previous study showed and translated toward the chromaticity of simulated illumination. In conclusion, the constant shape of luminosity threshold function supports our hypothesis and its translation and statistical analysis suggests that the visual system determines the degree of chromatic translation based on surround colors.