On thinning gray-scale patterns

We describe a thinning algorithm to find a skeletal representation of a gray-scale pattern in terms of digital lines mainly located along the ridges of the pattern. The algorithm has been designed to deal with patterns characterized by hollows of different size and depth, and is based on removal operations successively applied to pixels with higher and higher gray-value. Differently from most existing algorithms, any hollow, whose depth is significant in the problem domain is regarded as an additional component of the background and contributes with a loop to the structure of the skeleton. The obtained results are in good agreement with what an observer could interpret as a stylized version of the gray-scale pattern.