Đổi tên file
    #ifdef LINUX
            filename = filename.substr(0, filename.size() - 1);// linux tính xuống dòng là một ký tự
    #endif
            string fname_out = filename.substr(0, filename.size() - 4) + "jpg";
    #ifdef LINUX
            fname_out = filename.substr(0, filename.size() - 5) + "jpg";
    #endif

Cut a roi
    x = 2396; y = 267; width = 123; height = 123;
    Mat img_tmp;
    img(cv::Rect(x, y, width, height)).copyTo(img_tmp);
    //draw the roi
    rectangle(img, cv::Point(x, y), cv::Point(x + width, y + height), color, 3, 8, 0);
    
Subtract an image
    Mat image = imread(folder_in + "/" + filename, IMREAD_GRAYSCALE);
    Mat diff;
    absdiff(image, image_average, diff);
    imwrite(folder_out + "/" + filename, diff);