Acquiring bump maps from curved objects

Abstract

A method and system for obtaining and processing acquired images of an object to extract a small scale geometry (a bump map) of the object that is independent of object curvature. The method includes steps of (a) operating N (where N>3) light sources and an image input device placed at a distance from the object such that different regions of the object are illuminated by each of the multiple light sources; (b) obtaining multiple images of the object, one for each of the light sources with the other light sources turned off; (c) processing the images to derive three images, each corresponding to a component of surface normals of the object relative to directions to three of the light sources; (d) removing an effect of large scale surface shape from the derived images of the surface normals by computing low spatial frequency images from the derived images; (e) for a section or sections of the images for which the small scale geometry is to be acquired, determining transformations from the surface normals represented by the low spatial frequency images to the normals of a planar surface; (f) applying the transformations to the derived surface normal images to obtain the normals of the small scale surface variations applied to a flat plane; (g) adjusting a spacing of the values for the normals to account for foreshortening due to curvature by expanding the distances using directional derivatives computed from the surface normals at each point in the image; and (h) obtaining regularly spaced images of new surface normals by sampling the spatially adjusted images onto a new, regularly spaced image.