ESTIMATION OF ILLUMINANT DIRECTION, ALBEDO, AND SHAPE FROM SHADING

A robust approach to recovery of shape from shading information is presented. Assuming uniform albedo and Lambertian surface for the imaging model, we first present methods for the estimation of illuminant direction and surface albedo. Two methods for estimating the azimuth of the illuminant are presented. One is based on local estimates on smooth patches. The other method uses shading information along image contours. The elevation of the illuminant and surface albedo are estimated from image statistics, taking into consideration the effect of self-shadowing. With the estimated reflectance map parameters, we then compute the surface shape using a new procedure that implements the smoothness constraint by requiring the gradients of reconstructed intensity to be close to the gradients of the input image. The new algorithm is data driven, stable, updates the surface slope and height maps simultaneously, and significantly reduces the residual errors in irradiance and integrability terms. A hierarchical implementation of the SFS algorithm is presented. Typical results on synthetic and real images are given to illustrate the usefulness of our approach.