Delineation of elongated sub-patterns in a piecewise constant foreground

A procedure useful to give evidence to the perceived linear structure of a gray-tone pattern is presented, which allows one to delineate its locally higher intensity regions with a connected set of simple digital lines, qualitatively analogous to the skeleton representation computed in the case of binary images. The pattern is regarded as constituted by a number of regions with constant gray-value, and the skeletonization is based on the detection of suitable pixels on its Distance Transform, computed according to the city-block distance. The set delineating the pattern is found by reducing the set of the skeletal pixels to a one-pixel-thick set, and by pruning part or all of its peripheral branches.