Abstract
The mode of color appearance (“mode”) is a concept proposed by Katz (1935), and the names of the modes were defined in relation to materials. As exemplified with an orange ray that turns into brown surface, the mode can be a strong modulator of color perception. The present study investigated the characteristics of mode perception, as a first step to study its effect on color perception. All test stimuli were computer-generated images presented on the screen of an organic EL display with a very wide dynamic range of luminance level: from 1.0E-7 to 1.5E+2 (=150) [cd/m2]. A rotating spheroid was rendered with several surface textures: (1) three reflectance levels of uniform gray surface (glossy or matte), and (2) fabric patterns (organic cotton or velvet): organic cotton yielded a compelling textile perception, but velvet was ambiguous. The sphere was presented in one of four luminance levels of background, including a complete black. Seven subjects rated the mode and lightness, one by one, for two times. The lightness ratings were a linear function of the surface reflectance, regardless of surface texture. However, the mode ratings varied remarkably with surface texture for similar lightness spheres; the “organic cotton” was rated as “almost surface,” the uniform gray was “almost luminous,” and the “velvet” was the intermediate. For ambiguous material surfaces, surround luminance affected both lightness and mode ratings, but the glossiness did not. Therefore, lightness and mode perception are clearly different, and the mode judgment was strongly affected by the material surface property.