Impossible shaded images
- 1 January 1993
- journal article
- Published by Institute of Electrical and Electronics Engineers (IEEE)
- Vol. 15 (2) , 166-170
- https://doi.org/10.1109/34.192489
Abstract
It is shown that shaded images that cannot have originated from a uniformly illuminated, smooth continuous surface with uniform albedo exist. The typical condition where this occurs is when a dark area (corresponding to a region of high gradient) is surrounded by a lighter region (with low gradient). For this to correspond to a real surface, it must be established that there is a local extremum or area of lower gradient inside the dark region. This, in turn, will show up as either a light area in the image or an orientation discontinuity in the surface (thus violating either intensity or smoothness constraints). The impossibility of a shaded image can be established by counting the number of extrema inside a region corresponding to an isolated surface patch.Keywords
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