Edge detection is the approach used most frequently for segmenting images based on abrupt changes in intensity. Edge models are classified according to their intensity profiles. A step edge involves a transition between two intensity levels occurring ideally over the distance of one pixel. Step edges occur, in images generated by a computer for use in areas such as solid modelling and animation. The Canny edge detection is derived using a step-edge model. Digital images have edges that are blurred and noisy, with the degree of blurring determined principally by limitations in the focusing mechanism and the noise level determined principally by the electronic components of the imaging system. In such cases edges are more closely modelled as having intensity ramp. The slope of the ramp is inversely proportional to the degree of blurring in the edge. A third model of an edge is the roof edge, are models of lines through a region, with the base of a roof edge being determined by the thickness and sharpness of the line.
