Hole Detection
Small holes are important features that can be used very conveniently to locate complex objects. If holes are very small, 3 × 3 or slightly larger window operators can be used to locate them. If large and circular, the Hough transform may be suitable. If of intermediate size, special fast-acting methods may be useful. This chapter analyzes the situation and compares the available methods and their properties.
• the basic template matching method for hole detection.
• the lateral histogram method for hole detection.
• how ambiguities can be eliminated with the lateral histogram method.
• how speed of processing can be estimated.
• limitations of the lateral histogram method.
• how illumination sets a limit on detection sensitivity and accuracy of location.
This chapter contrasts different methods for detecting an important type of image feature. Speed, sensitivity, and accuracy are all found to be important parameters, and the lighting system is found to be unexpectedly important if accuracy of location is crucial.