Depth from focal gradient analysis using object texture removal by albedo normalization

摘要

The invention provides a method and apparatus for obtaining a range image of an object. The method includes the act of "albedo normalization", i.e., removing the effects of object reflectance using a structured illumination image of the object and a uniform illumination image of the object to provide an albedo-normalized image. This image is then processed using a focus measure to provide a focal image, which image is then used to provide a range image. The invention substantially removes the effects of object reflectance from an image acquired using structured illumination, so that only the structured illumination pattern and its degree of focus/defocus remains. Albedo normalization is achieved by dividing an image of an object taken under structured illumination by a corresponding image of the object taken under uniform illumination. The albedo normalization act removes the primary source of noise in range images obtained using a depth from defocus or depth from focus of structured illumination technique, by removing spurious image frequencies from the image before processing by a focus measure. The albedo normalization act permits the depth from defocus and depth from focus techniques to be used for one or more focal positions, and over a broad range of materials of interest in machine vision.