canny算子主要用于边缘检测，分为四步，第一步是高斯平滑、第二步是计算梯度，第三步是非极大限制边缘检测、第四步是滞后修复-canny operator is mainly used for edge detection, is divided into four steps, the first step is Gaussian smoothing, the second step is to calculate the gradient, the third step is non-edge