Recovering shape from shading and contour

The classical approach to shape from shading problems is to find a numerical solution of the image irradiance partial differential equation. It is usually assumed that the parameters of this equation (the light source direction and surface albedo) can be estimated in advance. For images which contain shadows and occluding contours, this decoupling of problems is artificial and the classical approach fails. We develop a new approach to solving these equations using the image geometric structures instead of the image photometric structure. Our approach is based on modern differential geometry, and solves for light source and surface shape changes concurrently. Local scene elements (scenels) are estimated from the shading flow field and the tangent field, and smoothness, material, and light source compatibility conditions resolve them to consistent scene descriptions. Shadows and related difficulties for the classical approach are discussed