Inspecting specular lobe objects using four light sources

The authors propose a noncontact method of measuring surface shape and surface roughness. The method uses four lights which sequentially illuminate the object under inspection, and a video camera for taking images of the object. Conceptually, the problem has three parts: shape extraction, pixel segmentation, and roughness extraction. The shape information is produced directly by three-light and four-light photometric stereo methods. After shape information is obtained, statistical segmentation techniques can be applied to determine which pixels are specular and which are nonspecular. Then, the specular pixels and shape information, and a simplified Torrance-Sparrow reflectance model can be used to determine the surface roughness. The method has successfully been applied to a number of synthetic and real objects