Bump and depression detection on ceramic tiles

We discuss the problem of choice of illumination in the context of inspecting the surface of ceramic tiles for the identification of possible structural imperfections, manifesting themselves as small bumps or depressions. In our case the requirement is maximal detectability and our problem simplifies into choosing the optimal angle of illumination in order to detect the objects we are interested in, after we adequately model them. For the detection of bumps on the surface of ceramic tiles a linear CCD sensor is used. It scans the ceramic tile line by line and it is orientated in such a way that the columns of the image are aligned with the direction of the illumination. In this paper we model a bump as a small local rounded convex deviation of the surface. Its abstract model can be represented by a part of a sphere. (3 pages)