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Phillip Marlow, Barton Anderson; The misperception of opacity, reflectance, and 3D shape. Journal of Vision 2018;18(10):224. doi: 10.1167/18.10.224.
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In order to recover scene properties, the visual system is confronted with disentangling the contributions of the light field from material properties and surface geometry. We previously proposed that the visual system uses the covariation of intensity and surface orientation to distinguish opaque and translucent surfaces. This covariation should be high for opaque surfaces and low for translucent materials, and stronger for convexities than for concavities (which can be dominated by vignetting and inter-reflections). Here, we show it is possible to induce dramatic misperceptions of the opacity, shape, and reflectance of Lambertian surfaces by simply varying the dominant illumination direction of the light field. A bumpy plane with Lambertian reflectance was rendered in either a diffuse (Ganzfeld) or natural light field. The orientation of the light field, and the albedo and relief of the bumpy plane, were parametrically varied. Observers matched the material appearance of each surface by adjusting the sub-surface scattering and specular reflectance parameters of a cube that was rendered in a different natural light field. The results show that the Lambertian surface in oblique illumination appears opaque and matte, whereas the matches for the same surface in frontal or diffuse illumination were very translucent and glossy. We then assessed the contributions of the convexities and concavities on perceived shape and material properties. Our results show that the perceived shape of the concavities appears to depend on information derived from the convexities, but the perceived reflectance and opacity depended on information derived from both; the perception of translucency is strongest when intensity covaries with relief depth rather than surface orientation. These results show that the perception of opacity, reflectance, and 3D shape can be dramatically affected by the light field, and provide new insights into the information used to compute these scene attributes.
Meeting abstract presented at VSS 2018
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