1. INTRODUCTION
Mathematical morphology [1] is a classic nonlinear image processing technique that has been successfully applied to the processing of remotely sensed imagery [2]. Based on set theory, binary morphology was established by introducing fundamental operators applied to two sets [1]. One set is processed by another one having a carefully selected shape and size, and known as the structuring element (SE), which is translated over the image. The SE acts as a probe for extracting or suppressing specific structures of the image objects, checking that each position of the SE fits within the image objects. Morphological operations have extended to grayscale images by viewing these data as an imaginary topographic relief. In practice, set operators directly generalize to gray-tone images.