图像rows,columns与坐标的对应关系

OpenCV Images

转自：https://blog.csdn.net/sc944201630/article/details/82222909

行列与坐标系对应关系
行rows：Y (Height)
列cols：X (Width)

在Mat类型变量访问时下标是反着写的，即按照(y, x)的关系形式访问，下面通过代码展示来说明这一点。

    #include "opencv2/core.hpp"
    #include "opencv2/imgproc.hpp"
    #include "opencv2/highgui.hpp"
    #include 
    
    using namespace cv;
    using namespace std;
    
    int main()
    {
        Mat mat_src = Mat::eye(3, 4, CV_8UC1);
    
        cout << "mat_src :" << endl;
        cout << mat_src    << endl;
    
        cout << endl;
        cout << "Rows : " << mat_src.rows << endl;
        cout << "Cols : " << mat_src.cols << endl;
    
        //注: mat_src.at(y, x), 下标关系为: y-x
        mat_src.at<float>(0, 2) = 2; 
        mat_src.at<float>(2, 0) = 4;
    
        cout << endl;
        cout << "mat_src :" << endl;
        cout << mat_src    << endl;
    
        return 0;
    }

Matlab Images

From https://ww2.mathworks.cn/help/images/images-in-matlab.html
An image composed of 200 rows and 300 columns of different colored dots would be stored in MATLAB as a 200-by-300 matrix.