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How direction of illumination affects visually perceived surface roughness.
Yun-Xian Ho1, Michael S Landy, Laurence T Maloney
1Department of Psychology, New York University, New York, NY 10003, USA. yunxian.ho@nyu.edu
Journal of Vision
|August 3, 2006
Summary
Human perception of surface roughness changes with lighting. Decreasing illuminant angle made surfaces appear rougher, and this effect persisted even with added scene context.
Area of Science:
- Visual perception
- Computer graphics
- Surface properties
Background:
- Understanding how humans perceive surface roughness is crucial for realistic computer graphics and material science.
- Lighting conditions significantly influence visual cues, complicating consistent perception of surface attributes.
Purpose of the Study:
- To investigate the impact of varying lighting conditions on the visual estimation of surface roughness.
- To identify cues used by observers and analyze deviations from roughness constancy.
Main Methods:
- Computer-generated 3D surfaces were rendered under mixed diffuse and punctate lighting.
- The angle of the punctate light source relative to the surface was systematically varied.
- Observers compared pairs of surfaces and judged roughness, with and without contextual scene elements.
Main Results:
- Surface roughness perception was strongly correlated with the illuminant angle; smaller angles led to perceived increased roughness.
- The presence of contextual objects in scenes did not improve roughness constancy.
- Four novel lighting-dependent cues ('pseudocues') were identified that explain systematic perceptual errors.
Conclusions:
- Perception of surface roughness is highly sensitive to illuminant angle, leading to non-constant perception across different lighting.
- Observer deviations from roughness constancy can be modeled by the influence of these identified 'pseudocues'.