Relief extraction of rough textured reflecting surface by image processing

Abstract

Rough surface relief extraction is generally made by a mechanical method using a tactile sensor or by using an auto-focus laser sensor. With these sensors we can estimate surface relief from the analysis of a series of profiles. Since these measurements spend a lot of time, we hope that we can determine the relief by image processing. Several methods in the field of image processing have been proposed for relief extraction, such as shape from shading, optical flow, shape from focus and photometric stereovision. Our works are based on the photometric stereovision. In 1980, Woodham indicated that the relief of a Lambertian surface can be determined by the exploitation of a photometric model, which takes into account camera and light source positions according to the plan of surface. The proposed model expresses the gray level on the image according to the local relief variations. Three images of the same relief obtained under different angles of lighting are used to reconstruct the surface relief. From the method of Woodham, several important ameliorations have been proposed by other researchers. But a limit study in section 2.1.3 proves that the above methods worked with Lambert's model is adapted to the diffuse reflection, but not to the specular reflection. Thus, we propose another method to extract the relief of rough textured reflecting surface. In the proposed method, we show that the diffuse and specular components of the acquired images can be decomposed in two independent components. The diffuse component can be processed by Lambert's model, the specular component can be processed according to the position knowledge of facets. Finally, section 3 presents the experimental results obtained by this method, and compares measurement precision with the experimental results obtained by Lambert's model.