A structural matching for two-dimensional visual pattern inspection

A structural matching method to inspect the two-dimensional visual pattern is proposed. The pattern is represented by a tree where its nodes contain the polygonal-boundary information derived from the pattern image. To inspect whether or not the inspected pattern is defective, the matching process first checks if the tree constructed from the pattern is isomorphic to the one constructed from the standard defect-free. If they are not isomorphic, the process stops and concludes that the pattern is defective. Otherwise, it performs the second matching step using the polygonal-boundary matching function. The suggested method is illustrated for the PCB inspection and shown to have the much lower time complexity than the conventional methods using graph matching.