A thinning algorithm on 2d gray-level images

Thinning on binary images is widely discussed in the past three decades. A binary image can be obtained by thresholding a gray-level image. For preventing possible information losses in the thresholding process, it may be natural to design thinning algorithms directly on the original gray-level images. This paper proposes a two-step template-based thinning algorithm on gray-level images. The first step of the algorithm is to extract 4-connected gray-level skeletons from gray-level objects. The second step is to extract 8-connected gray-level skeletons from the consequent result of the first step.