C++ 中 opencv Mat 变量的常见运算

1. cv::Mat 的属性 

cv::Mat img ;

img = cv::imread( img_path, CV_LOAD_IMAGE_COLOR ) ;

if ( !img.data )

    std::cout << "Could not open or find file " << img_path << std::endl ;

int img_rows =  img.rows ; Mat 的高宽属性

int img_cols = img.cols ;

for( int h; h<img_rows; h++)

     for( int w; w<img_cols; w++ )

       {

        img.at<uchar>(h, w ) ; note the order of the height and cols

       }                                         similar as that of matlab. 

 cv::Mat img( height, width, CV_8UC1, cv::Scalar(0) ) ;

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cv::Rect roi ;

roi.x = 0 ;  start index of width 

roi.y = 0 ; start index of height

roi.width = (int) img_cols/2 ; 

roi.height = (int) img_rows/2 ;

cv::Mat c