Geometry of shadows

David C. Knill, Pascal Mamassian, Daniel Kersten
1997 Optical Society of America. Journal A: Optics, Image Science, and Vision  
Shadows provide a strong source of information about the shapes of surfaces. We analyze the local geometric structure of shadow contours on piecewise smooth surfaces. Particular attention is paid to intrinsic shadows on a surface: that is, shadows created on a surface by the surface's own shape and placement relative to a light source. Intrinsic shadow contours provide useful information about the direction of the light source and the qualitative shape of the underlying surface. We analyze the
more » ... nvariants relating surface shape and lightsource direction to the shapes and singularities of intrinsic shadow contours. The results suggest that intrinsic shadows can be used to directly infer illuminant tilt, qualitative global surface structure, and, at intersections with surface creases, the concavity/convexity of a surface. We show that the results obtained for point sources of light generalize in a straightforward way to extended light sources, under the assumption that light sources are convex.
doi:10.1364/josaa.14.003216 pmid:9392900 fatcat:yfz64vnz7zfybkrf26kkmbtqxm