In grey-level image processing, images of typical scenes contain large areas of gradual intensity change, called segments, bounded by narrow regions of very rapid intensity change, called edges. An edge detector is a procedure or rule that locates a series of points, arranged roughly in a line, where rapid intensity changes have occurred. A set of edges can then be used by other operators, such as line finders, to build up the outline of object features. Many different forms of edge detectors have been developed in image processing, including the Laplacian operator.