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Bei Xiao, Bruce Walter, Ioannis Gkioukelas, Todd Zickler, Edward Adelson, Kavita Bala; Looking against the light: how perception of translucency depends on lighting direction and phase function. Journal of Vision 2014;14(10):1316. doi: https://doi.org/10.1167/14.10.1316.
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© ARVO (1962-2015); The Authors (2016-present)
Translucency is an important aspect of material appearance. To some extent, humans can estimate translucency in a consistent way across different shapes and lighting conditions, i.e., to achieve translucency constancy. However, Fleming and Bülthoff (2005) have shown that there can be large failures of constancy with respect to lighting direction changes. Here, we explore the interaction of shape, illumination, and degree of translucency constancy more deeply, by including in our analysis the variations in translucent appearance that are induced by the shape of the scattering phase function. This is an aspect of translucency that has been largely neglected. We used appearance matching to measure how perceived translucency depends on both lighting and phase function. The stimuli were rendered scenes that contain a figurine and the lighting direction is represented by a spherical harmonic basis function. Observers adjusted density of a match figurine under one lighting condition to match the material property of a target figurine under another lighting condition. Across the trials, we varied both the lighting direction and the phase function of the target. The phase functions were sampled from a 2D space that captures most of the perceptual variation in appearance (Gkioulekas et al. 2012). We find that degree of translucency constancy depends strongly on the phase function's location in the 2D space, suggesting that the space captures useful information about different types of translucency. We compare the case of a torus, which has a simple smooth shape, with that of the figurine, which has more complex geometric features. The complex shape shows a greater range of apparent translucencies, and also a higher degree of constancy failure. In summary, humans show significant failures of translucency constancy across changes in lighting direction, but the effect depends both on the shape complexity and the translucency phase function.
Meeting abstract presented at VSS 2014
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