Question

I would like to make the buffer of cv::mat point to the buffer of QImage but not copy
the data of QImage into the cv::mat.

cv::Mat const reference_qimage_to_mat(QImage const &img, int format)
{
    cv::Mat mat(img.height(), img.width(), format);

    for(int i = 0; i != mat.rows; ++i)
    {
        //pseudo code, wouldn't work
        //mat.ptr(i) = img.scanLine(i);
    }

    return mat;
}

I try to search the answer by google but I could only find how to copy
the data of QImage into cv::mat.Thanks

Answer 1

the cv::Mat object is simply a header for the image data, so you can do it upon your object construction:

cv::Mat mat(img.height(), img.width(), type, img.bits());

where type depends on your data, CV_8UC1 for single channel, CV_8UC3 for RGB, etc.