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A prior for global convexity in local shape from shading

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http://pubman.mpdl.mpg.de/cone/persons/resource/persons83839

Bülthoff,  HH
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Langer, M., & Bülthoff, H.(2000). A prior for global convexity in local shape from shading (81).


Cite as: http://hdl.handle.net/11858/00-001M-0000-0013-E4AA-7
Abstract
To solve the ill-posed problem of shape-from-shading, the visual system often relies on prior assumptions, for example, that the illumination is from above or that the viewpoint is from above. Here we demonstrate that a third prior assumption is used, namely that the surface is globally convex. Using unfamiliar randomly corrugated surfaces, we find that performance in a local shape discrimination task is significant higher when the surfaces are globally convex than when they are globally concave. The results are surprising because the qualitative global shape of the surfaces are perceptually unambiguous. The results thus generalize findings such as the hollow potato illusion (Hill H. Bruce V. 1994) which considered global shape perception only.