Using gpu::GpuMat in OpenCV C++

Question

I would like to know how can I modify a gpu::GpuMat. In fact I would like to know if it is possible to use a gpu::GpuMat like a cv::Mat.

I would like to do something like that:

    cv::namedWindow("Result");
    cv::Mat src_host = cv::imread("lena.jpg", CV_LOAD_IMAGE_GRAYSCALE);
    cv::gpu::GpuMat dst, src;
    src.upload(src_host);


    for (unsigned int y = 0; y < src.rows; y++){
        for (unsigned int x = 0; x < src.cols; x++){
            src.at<uchar>(y,x) = 0;
        }
    }

    cv::Mat result_host;
    dst.download(result_host);
    cv::imshow("Result", result_host);
    cv::waitKey();
}
catch(const cv::Exception& ex)
{
    std::cout << "Error: " << ex.what() << std::endl;
}
return 0;

It seems to be not possible. Does someone know an alternative ? Do I have to download my gpu::GpuMat to a cv::Mat each time I want to make something ? Thanks in advance

Edit: I could probably use gpu::PtrStepSz (have to test...)

I don't really see how this is a CUDA programming problem. Perhaps you could remove the CUDA tag from the question? — talonmies
– talonmies, Commented Jul 16, 2013 at 16:01
I want to use gpu::Mat which is provided by Opencv over Cuda... — Poko
– Poko, Commented Jul 16, 2013 at 16:06
Yes, but nothing in your code or question is actually anything to do with CUDA, only OpenCV classes which tangentially refer to abstractions with CUDA buried inside them somewhere. By the same logic you should tag your question with "windows" or "linux", because your code runs OpenCV over the top of the operating system as well.... — talonmies
– talonmies, Commented Jul 16, 2013 at 17:09

vinograd47 · Accepted Answer · 2013-07-16 16:32:31Z

12

GpuMat is allocated in GPU memory. You can't modify it from CPU code. You can

Set all matrix pixels to the same value (setTo method).
Fill data on CPU using cv::Mat and then upload it to GpuMat.
Implement your own CUDA kernel and fill GpuMat in it.

answered Jul 16, 2013 at 16:32

vinograd47

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1 Comment

Poko Over a year ago

Thanks ! that's what I was thinking ... :/

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