hình ảnh quang học của những cảnh thực sự, thường không có cạnh bước bởi vì khử răng cưa thấp vượt qua bộ lọc trước khi làm giảm số hóa độ dốc cạnh trong hình ảnh kỹ thuật số gây ra bởi bất kỳ thay đổi độ sáng đột ngột trong bối cảnh đó. Các hồ sơ cá nhân một chiều của một dòng được hiển thị trong Hình . | 466 EDGE DETECTION FIGURE . One-dimensional continuous domain edge and line models. of optical images of real scenes generally do not possess step edges because the antialiasing low-pass filtering prior to digitization reduces the edge slope in the digital image caused by any sudden luminance change in the scene. The one-dimensional profile of a line is shown in Figure . In the limit as the line width w approaches zero the resultant amplitude discontinuity is called a roof edge. Continuous domain two-dimensional models of edges and lines assume that the amplitude discontinuity remains constant in a small neighborhood orthogonal to the edge or line profile. Figure is a sketch of a two-dimensional edge. In addition to the edge parameters of a one-dimensional edge the orientation of the edge slope with respect to a reference axis is also important. Figure defines the edge orientation nomenclature for edges of an octagonally shaped object whose amplitude is higher than its background. EDGE LINE AND SPOT MODELS 467 FIGURE . Two-dimensional continuous domain edge model. Figure contains step and unit width ramp edge models in the discrete domain. The vertical ramp edge model in the figure contains a single transition pixel whose amplitude is at the midvalue of its neighbors. This edge model can be obtained by performing a 2 X 2 pixel moving window average on the vertical step edge model. The figure also contains two versions of a diagonal ramp edge. The singlepixel transition model contains a single midvalue transition pixel between the regions of high and low amplitude the smoothed transition model is generated by a 2 X 2 pixel moving window average of the diagonal step edge model. Figure also presents models for a discrete step and ramp corner edge. The edge location for discrete step edges is usually marked at the higher-amplitude side of an edge transition. For the single-pixel transition model and the smoothed .
