根据CNNAY算法的4个步骤
1. 用高斯滤波器平滑图像；（图像去噪）
2. 用一阶偏导有限差分计算梯度幅值和方向；（特征增强）
3. 对梯度幅值进行非极大值抑制 ；（边缘检测）
4. 用双阈值算法检测和连接边缘。（形态学处理）
编写的边缘检测程序，简单实用(There are four parts of Canny edge detection:
1. smoothing the image with Gauss filter; (image denoising)
2. calculate gradient amplitude and direction by first order partial derivative finite difference method (feature enhancement)
3. non maximum suppression of the gradient amplitude; (edge detection)
4. detect and connect edges with double threshold algorithm. (morphological treatment))