Abstract
The eikonal equation can have an infinite number of solutions when the image has critical points. We exhibit a family, indexed by a continuous parameter, of non isomorphic surfaces with one critical point, which give the same simple image. Hence, shape from shading can be an ill-posed problem when no additional condition on the shape is imposed, even when the image has critical points. Also, deformations without distortion are possible, i.e., there can exist a continuous deformation of the surface which does not modify its image.
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Durou, JD., Piau, D. Ambiguous Shape from Shading with Critical Points. Journal of Mathematical Imaging and Vision 12, 99–108 (2000). https://doi.org/10.1023/A:1008361021281
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DOI: https://doi.org/10.1023/A:1008361021281