Abstract
Previous studies have shown that chromatic information on object images, such as chromatic difference between specular highlight and diffuse shading, enhances perceived gloss (“color-gloss effect”, hereafter). However, the mechanisms underlying this color-gloss effect is still unclear. Here we aimed to psychophysically elucidate perceptual and image factors which yield the color-gloss effect. In experiment 1, we measured perceived glossiness on images of colored objects with different diffuse reflectance and surface roughness. The object images were first created as achromatic images with a computer-graphics software, and then were colored with various hue chromaticity while luminance was unchanged. There were two coloring conditions: D condition and SD condition. In D condition only the diffuse components were colored, while in SD condition both the diffuse and specular components were colored. The glossiness was measured in a paired comparison experiment; two object images with different hues were simultaneously presented to the observer as stimuli, and the observer responded which object seemed glossier with a 2AFC manner. The preference scale values were estimated according to the Thurston’s case V model after the experiment. The results exhibited mainly three important characteristics: 1) the color-gloss effect was stronger in SD condition than D condition, 2) the color-gloss effect increased with diffuse reflectance and roughness in D condition even though they decrease color contrast between specular and diffuse components, and 3) the color-gloss effect largely differed across the hues in both D and SD conditions. To examine the cause of this trend across hues, we measured the Helmholtz-Kohlrausch (H-K) effects on different luminance, saturation and hue conditions in experiment 2, and found that the trend across hues in experiment 1 was moderately correlated with H-K effect. These results suggest the H-K effect, not the color contrast between the specular highlights and diffuse shadings, predominantly contributes to the color-gloss effect.