Imgcodecs example.
#include <iostream>
using namespace std;
int main()
{
    
    
    for (int r = 0; r < img.dims_[1]; ++r) {
        for (int c = 0; c < img.dims_[0]; ++c) {
            *img.
Ptr({ c, r, 0 }) = 255;
            *img.Ptr({ c, r, 1 }) = (r / 2) % 255;
            *img.Ptr({ c, r, 2 }) = (r / 2) % 255;
        }
    }
    ImWrite(
"example_imgcodecs.png", img);
     if (!
ImRead(
"example_imgcodecs.png", img)) {
         return EXIT_FAILURE;
    }
    cout << "Successfully read a color image" << endl;
        return EXIT_FAILURE;
    }
    cout << "Successfully read a grayscale image" << endl;
    return EXIT_SUCCESS;
}