THINNING METHODOLOGIES - A COMPREHENSIVE SURVEY

This article is a comprehensive survey of thinning methodologies. It discusses the wide range of thinning algorithms, including iterative deletion of pixels and nonpixel-based methods, whereas skeletonization algorithms based on medial axis and other distance transforms will be the subject matter of a subsequent study. This self-contained paper begins with an overview of the iterative thinning process and the pixel-deletion criteria needed to preserve the connectivity of the image pattern. Thinning algorithms are then considered in terms of these criteria as well as their modes of operation. This is followed by a discussion of nonpixel-based methods that usually produce a center line of the pattern directly in one pass without examining all the individual pixels. Algorithms are considered in greater detail and scope here than in other surveys, and the relationships among them are also explored.