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Material-dependent shape distortion by local intensity order reversal

52.26, Tuesday, 19-May, 10:45 am - 12:30 pm, Talk Room 2
Session: Color Perception: Material properties

Shin'ya Nishida1, Masataka Sawayama1, Takeaki Shimokawa2; 1NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation, JAPAN, 2ATR Neural Information Analysis Laboratories, Advanced Telecommunications Research Institute International, JAPAN

The visual image of an object is formed by a complex interaction among the material (reflectance), geometry (shape) and lighting of the object. How, and how well, the visual system recovers these image-formation components from the resultant image is a longstanding problem in vision science. With constant shape and lighting, material changes drastically alter the intensity distribution of the object image. However, as long as these changes can be ascribed to variations in parameters for diffuse and specular reflectance (e.g., addition of highlights), they had only minor effects on the local intensity orders (Sawayama & Nishida, VSS2014). This observation led us to a hypothesis that the human shape-from-shading processing may be sensitive to the local intensity order information, while not to the steepness of intensity gradient to which material processing is very sensitive. To test this hypothesis, we examined human shape-from-shading perception for local-gradient-modulated images that shared the local intensity order map, but not the gradient magnitude map, with the original matte object images. Specifically, we randomly modulated the steepness of the intensity gradient between adjacent iso-intensity contours of the image. In the experiment, observers adjusted the tilt/slant of a gauge probe with the apparent surface normal direction. We found that the perceived shapes of the local gradient-modulated images were similar to those of the original images. We also examined the shape perception for objects with asperity scattering, a class of reflectance uncovered by diffuse/specular models, producing the appearances of velvet and peach. As compared to the matte image, the asperity scattering distorted the perceived shape when it caused local reversals of intensity order, while not when the asperity scattering completely reversed the intensity order map. These findings support the hypothesis that human shape-from-shading relies dominantly on the local intensity order information.

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