An automatic visual inspection method of pattern using a circular feature extraction filter

The purpose of this paper is to describe a method for automatic visual inspection of patterns, such as bare-printed circuit boards (PCB´s). The method detects faults of patterns by comparing an input pattern to be inspected with the reference one after features extraction from each of them. For the feature extraction, a circular local filter in the method is used to recognize the pattern´s interior points, exterior points, boundary points, the boundary´s direction, and the boundary´s curvature. The ability of the filter that detects the difference between two boundaries of different curvature is also presented.