Geometry of shadows

David C. Knill, Pascal Mamassian, Daniel Kersten

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


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 invariants 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.

Original languageEnglish (US)
Pages (from-to)3216-3232
Number of pages17
JournalJournal of the Optical Society of America A: Optics and Image Science, and Vision
Issue number12
StatePublished - Dec 1997


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