Nonlinear multiresolution: a shape-from-shading example

A method for image resolution reduction that simulates the reduction of shape resolution and is to be used with shape-from-shading algorithms is presented. Resolution reduction is used for accelerating shape-from-shading algorithms using multiresolution pyramids. The goal of this correspondence is to show that resolution reduction based only on image intensities can be inferior to resolution reduction using knowledge of the surface reflectance. This is true for all cases of parameter estimation from intensity images, when the intensity is not a linear function of the parameters. Since optical reduction of images, as when moving a camera away from the object, is a simple gray-level averaging a question is cast on the general scheme of shape-from-shading. It is concluded that for accurate shape-from-shading one needs to know the distance from the object, and the shape should also be known in advance