sentences:  Another class of operations is based on the notion of filtering with a structuring element.The structuring element is binary image, usually small, which is passed over the target image, in a similar manner to a filter in gray scale image processing.Since the pixels can only have two values, the morphological operations are erosion (any unset pixels within the structuring element cause the pixel to be unset) and dilation (any set pixels within the structuring element cause the pixel to be set).