In order to monitor, analyze, evaluate our skin about its aging, its health, and it alimentary status, presently the most efficient way is to analyze the dermal images using modern digital image processing techniques. As the preprocessing of this skin analyzing system, in this paper, we propose a method for extracting the centerlines of the creases meshing over our dermis in a clinical dermal image. The method includes the following steps: first of all, Feature space transformation, this is to map the pixels in the grayscale space into feature space according to the regional energy of these pixels. Secondly, Filtering, a morphological filter is designed to remove noises and spurious minima. The amount of filtering can be manually tuned to get a different result. Thirdly, marker selection, using the Top-hat transformation based on morphological reconstruction to get a reliable set of markers. Finally, Watershed transformation, the scheme is used to extract the central axes and form a network of lines. The experiment shows that this method is an effective one for the purpose of extracting roof-edge centerlines.