Algorithms for region description and modifications based on chain code transformations

A new approach to region description and interpretation based on chain code transformation is presented. Chain codes are used to obtain syntactic expressions for concave and convex parts of boundary lines in a picture. Using these syntactic expressions, an algorithm for filling concavities and finding the convex hull of a region is derived. This algorithm is also suited to describe a region in terms of a list of convexities and concavities, and to analyze regions where small gaps and thin bridges are involved. Then, it is shown that expansion and shrinking of 4-connected objects can be performed by means of a chain code transformation.