Fractal Dimensions of Pellicle Surfaces.

To quantify the fractal behavior and fractal dimensions of pellicle wrinkles, Frangi vesselness maps of pellicles were first binarized using intensity thresholding and then skeletonized using medial axis thinning algorithms (44). Short and isolated branches in the skeletons were pruned. A standard box-counting algorithm was applied to the skeleton images and the scaling exponents of the box counts to the box sizes were obtained to define the fractal dimensions (37, 45).