Piece-Wise Linear Approximation Of An Object Boundary From Freeman Chain Code

An algorithm is described to generate a polygonal approximation to an object boundary from the Freeman chain code using digital filters. In computer vision and pattern recognition, concatenation of digital straight lines is a simple and compact representation of the boundary of well behaved planar regions. Digital straight lines have often been used as features to track and recognize shapes and objects. To abstract digital straight lines, the chain code sequence is used as the input to two digital filters with different response characteristics. The difference between the outputs of the filters is used to detect corners; noisy line segments result in reduced corner detection accuracy. The algorithm also provides an estimate of the angle between neighboring lines and a basis for estimating the length of the line segments. Moreover, an extension of this algorithm may be used to detect quadratic segments in an object boundary.