Shaded image machining: a reverse engineering approach using computer vision techniques and analytical methods to reproduce sculptured surfaces
W.L. Ralph Ip, Martin Loftus · International Journal of Production Research · 1996
Recovering surface geometry from crafted masters is an essential process in the manufacture of production moulds and dies. Direct copying and reverse engineering strategies are used intensively to support the tool-making process but high labour skill and costly measuring equipment are necessary to realize the finished products. The aim of this paper is to report a new surface reproduction approach, which is based on the techniques of photometric stereo and shape from shading. The tool path planning parameters, surface normals and coordinates, are recovered from a group of halftone photographic images using a combination of the reversal of the Phong illumination model, and successive integration of the gradient parameters on linear reflectance maps. The halftone images are captured and processed using computer vision techniques. This data is used to drive a ball-nosed cutter under numerical control. The approach can produce surfaces as complex as the human figure, which are difficult to reproduce by conventional surface profile tracing and machining methods. The machining of the Venus de Milo sculptured surface, cited in the case study, proves that the new surface reproduction method is an alternative strategy which uses non-contact type surface profile assessment techniques.