The KGBR Viewpoint-Lighting Ambiguity and its Resolution by Generic Constraints

We describe a novel viewpoint-lighting ambiguity which we call the KGBR. This ambiguity assumes orthographic projection or an affine camera, and uses Lambertian reflectance functions including cast/attached shadows and multiple light sources. A KGBR transform alters the geometry (by a three-dimensional affine transformation) and albedo properties of objects. If two objects are related by a KGBR transform then for any viewpoint and lighting of the first object there exists a corresponding viewpoint and lighting of the second object so that the images are identical up to an affine transformation. The Generalized Bas Relief (GBR) ambiguity [1] is obtained as a special case of the KGBR. We describe generic viewpoint and lighting assumptions [5] and show that either, or both, resolve this ambiguity by biasing towards objects with planar geometry. In Proceedings International Conference on Computer Vision. Vancouver, British Columbia. 2001.