Effective Method for Circle Detection Based on Transformation of Chain Code Direction

There are two approaches generally used for detecting a circle object in a digital image, they are a circle detection method based on Hough Transform and a circle detection method based on geometrical characteristics. A circle detection method on the basis of object geometry based on edges tracking of objects and transformation of chain code direction is proposed. Firstly, the chain code of the edges of the object to be detected was traced and stored in a set of vector array. Then the process of selecting the edges of objects from a bunch of the chain code was conducted to select circle candidates by focusing on changing the chain code direction on each edge of the object. Finally, the process of determining whether the object edges are circle candidate or not was carried out. During the process, the determination of reference point calculation was very influential. To increase efficiency at that stage was conducted by selecting three reference points on the edges of the object based on the calculation of the transformation of chain code direction in sequence with a specified level of sensitivity. The test results based on a synthesis image that consists of a wide variety of circular shape provide good results in terms of efficiency and accuracy.