Abstract
Our visual scene frequently includes objects with translucent material properties such as silk curtains or plastic bags. Since they interact with incident lights in different ways from opaque objects, other image features can be produced depending on their three-dimensional shapes. For instance, the light transmittance of a thin translucent object tends to be higher when the surface normal is toward the direction of the eye than when it is slanted with regard to the eye direction. These physical properties can produce the following modulations in the image when the surface is slanted: 1) the image contrast of the background scene through the translucent surface decreased, and 2) the surface color (shading) of the translucent surface enhanced. To elucidate what image features the visual system relies on perceiving material and shape of translucent objects, the present study investigated each contribution of the background contrast and the translucent surface shading. The stimulus was synthesized by the image-based blending of a natural texture with the slant map of a corrugated CG sheet. Specifically, the blending consisted of the contrast modulation of the texture the slant map and the addition of the slant shading. When only the contrast modulation was applied, observers could perceive the translucent impression of the CG sheet, but not its three-dimensional shape. In contrast, when both the contrast modulation and the shading addition were applied, not only the translucent impression but also the three-dimensional shape impression could be obtained. Furthermore, the perceived shapes of translucent objects were similar to those obtained from their slant shading. These findings suggest that the contrast modulation of the background is effective translucent material perception, and for translucent shape perception the cue needs to be combined with luminance signals from the translucent surface shading.
Acknowledgement: This work was supported by JSPS KAKENHI Grant Number JP15H05915.