cannot access values of Mat returned from OpenCV functions

Question

I'm using cv::imread to load a image and do some processes with that image, but I don't know why I can't read values of the returned Mat from imread function. I used Mat.at method:

Mat iplimage = imread("Photo.jpg",1); //input
    for(int i=0;i<iplimage.rows;i++){
        for(int j=0;j<iplimage.cols;j++){
            cout<<(int)iplimage.at<int>(i,j)<<" ";
        }
        cout<<endl;
    }

But it appeared an error:

OpenCV Error: Assertion failed ( dims <= 2 && data && (unsigned)i0 < (unsigned)size.p[0] && (unsigned)(i1*DataType<_Tp>::channels) < (unsigned)(size.p[1]*channels()) && ((((Sizeof(size_t)<<28)|0x8442211) >> ((DataType<_Tp>::depth) & ((1 << 3) -1))*4) & 15) == elemSize1()) is unknown function, file: "c:\opencv2.2\include\opencv2\core\mat.hpp", line 517

But it is ok if I use the direct access way:

 Mat iplimage = imread("Photo.jpg",1); //input
     for(int i=0;i<iplimage.rows;i++){
         for(int j=0;j<iplimage.cols;j++){
        cout<<(int)iplimage.data[i*iplimage.cols + j]<<" ";                 
         }
    cout<<endl;
     }

Could anyone tell me how can I use the Mat.at method to access the above Mat? Thanks for your help!

fireant fireant · Accepted Answer · 2012-05-05T17:16:54

See this answer. In your case, the returned Mat is 3 dimensional, hence iplimage.at<int> fails the assertion, you just need to access the intensities in each channel like the way the mentioned answer explain.

cannot access values of Mat returned from OpenCV functions

4 Answers