The KGBR viewpoint-lighting ambiguity.
We address the visual ambiguities that arise in estimating object and scene structure from a set of images when the viewpoint and lighting are unknown. We obtain a novel viewpoint-lighting ambiguity called the KGBR that corresponds to a group of three-dimensional affine transformations on the object or scene geometry combined with transformations on the object or scene albedo. Our analysis assumes orthographic projection with an affine camera model. We include photometric cues, such as shadowing and shading, that we model using Lambertian reflectance functions with shadows (cast and attached) and multiple light sources (but no interreflections). We relate the KGBR to affine ambiguities in estimating shape and to the generalized bas-relief (GBR) ambiguity.