cv::Mat image = cv::imread('name.png')
for (int v = 0; v < rows; v++)
for (int u = 0; u < cols; u++)
image.at<uchar>(v,u)
https://blog.51cto.com/hongpangzi/3618613
https://www.cxybb.com/article/qq_42374559/109096761
https://www.cnblogs.com/Henry-ZHAO/p/12725254.html
https://www.cnblogs.com/guoben/p/12728390.html