Non-recursive thinning algorithms using chain codes

Thinning algorithms based on contour generation using chain codes have been demonstrated to be one of the fastest thinning algorithms. Up to now, recursive algorithms only have been developed. These algorithms are known to be susceptible to noise so that the appearance of certain skeletal branches depend on the order in which pixels are processed. This paper describes the development of Contour Generation Thinning (CGT) algorithms that are non-recursive. Two algorithms are presented, both of them involves the use of 4 sub-cycles. Additional data structures are incorporated in the chain code to ensure consistency in the propagation of contour pixels. In both algorithm, the 4-distance metric is used. The first algorithm erodes a 4-connected contour in an iteration The second algorithm remembers the state of the bitmap at the beginning of an iteration, with the result that an 8-contour is eroded.