Usefulness of boundary sequences in computing shape features for arbitrary shaped regions

A boundary sequence is a good representation of arbitrary shaped regions, but not directly used in computing shape features such as area, centroid, orientation, and so forth. In this paper we show that the shape features can be easily computed by using cross-sections derived from a boundary sequence. The cross-sections are vertical line segments in the region and can be determined by tracing the boundary sequence once. Furthermore, a boundary sequence extraction method is also proposed, which generates a boundary sequence for each region in a binary image by scanning the image only once. The proposed method works well even if a region has holes.