说明：  Canny认为一个优良的边缘检测算子应具有以下3个特性: ① 好的检测性能。不漏检真实边缘，也不把非边缘点作为边缘点检出，使输出的信噪比最大。 ② 好的定位性能。检测到的边缘点与实际边缘点位置最近。 ③ 唯一性。对于单个边缘点仅有一个响应。
(Canny think a good edge detector should have the following three characteristics: ① good detection performance. Not missed a true edge, nor the non-edge points as edge points detected, so that the maximum output signal to noise ratio. ② good positioning performance. Detected edge point and the actual location of the edge recently. ③ unique. For a single edge point only one response.)