I. Introduction
Mathematical morphological operations are widely used in, but no. 1imited to, the field of image processing. Many tasks, such as image pre-processing, segmentation, and object quantification, can be accomplished by morphological operations[1]. Sopharak et al. [2] used morphological operators to eliminate the eye optical disc during the detection of diabetic retinopathy exudates. In [3], Souza et al. adopted morphological closing and opening to segment obital regions and extraocular muscles interactively for quantification in diagnoses. De et al. [4] also employed opening and closing to find out the focused region in each of a series of multifocus images, and then used image fusion techniques to enhance the effective depth-of-field. These are just some recent applications of the mathematical morphology.