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Peter Vangorp, Roland W. Fleming; Glossiness of layered materials. Journal of Vision 2012;12(9):874. doi: 10.1167/12.9.874.
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Most previous work on gloss perception has examined the strength, and to some extent the spread (roughness), of the specular lobe in simple single-layered BRDFs. However BRDFs can be substantially more complex than this and it is interesting to ask how many additional perceptual dimensions there could be in the visual representation of surface reflectance qualities. To address this, we tested two-layered materials such as glossy plastics coated with a thin layer of varnish. Stimuli were renderings of irregularly-shaped objects under environment illumination, with either one Ward specular BRDF layer, or two such layers, with the same total specular reflectance but different roughness parameters. This creates both sharp and broad highlights simultaneously. Three differently-shaped objects were presented side by side: the target two-layered material in the middle, a single-layered approximation on one side, and the same two-layered material on the other. The two-layered materials were characterized by the average and difference of their Ward roughness parameters. The single-layered approximation used only the average Ward roughness parameter. This parameter was previously shown to be approximately perceptually linear. Subjects chose which material looked most similar to the target material in a 2AFC task. Within each block of the same average roughness parameter, a Quest staircase procedure was used to select the next pair of roughness values. Our results show that subjects do indeed discriminate between single-layered and two-layered materials when the difference between the two roughness parameters exceeds a certain threshold. This suggests that layers of glossy materials may be represented as orthogonal dimensions of gloss perception. It is however unclear whether more than two layers of gloss can still be discriminated. There is also evidence that the discrimination threshold depends on the average roughness parameter. Other possible factors include the diffuse and specular reflectance(s).
Meeting abstract presented at VSS 2012
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