A novel approach for circle detection based on the Hough transform is presented. It avoids the use of trigonometric functions in the transform equations. Instead of using traditional circle parameterization, which involves gradient direction information, this method uses three edge points to accumulate evidence for circle centers. The method can be extended to the detection of multiple circles where the gradient direction information is only used as a guide to select candidate edge points. A set of rules is proposed for the selection of triple edge points to define circle parameters which can guarantee that the points selected will not be on different circles. The responses for different circles produced in the parameter space using the proposed method are shown to be more compact around the true centers of the circles, thus, removing the need for postprocessing in the parameter space. The application of this method not only reduces the processing time, but also avoids the detection inaccuracy caused by the edge gradient direction errors.
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