How to multiply 2 OpenCV mats using a GPU
<p>In OpenCV, I can multiply an RGB 1920 x 1080 mat by a 3 x 3 Mat to change the color composition of my source Mat. Once my source mat is properly shaped, I can use the '*' operator to perform the multiplication. This operator is not available when using a cv::gpu::GpuMat.</p>

<p>My question is how would I format my input source Mat to use cv::gpu::gemm?Can I even use cv::gpu::gemm? </p>

<p>This is the only call that performs matrix multiplication in the OpenCV library from what I can tell. cv::gpu::gemm wants to see a CV_32FC1 , CV_64FC1 type Mat. The type I normally use with the CPU is CV_32FC3.</p>

<pre><code>//sourceMat is CV_32FC3 1920 x 1080 Mat
Mat sourceMat = matFromBuffer(data-&gt;bufferA, data-&gt;widthA, data-&gt;heightA);

//This is the color Matrix
float matrix[3][3] = {{1.057311, -0.204043, 0.055648},
{ 0.041556, 1.875992, -0.969256},
{-0.498535,-1.537150, 3.240479}};

Mat colorMatrixMat = Mat(3, 3, CV_32FC1, matrix).t();

//Color Correct the Mat
Mat linearSourceMat = sourceMat.reshape(1, 1080*1920);
Mat multipliedMatrix = linearSourceMat * colorMatrixMat;
Mat recoloredMat = multipliedMatrix.reshape(3, 1080);
</code></pre>

<p>Update:
As a test, I created the test routine:</p>

<pre><code>static int gpuTest(){

    float matrix[9] = {1.057311, -0.204043, 0.055648, 0.041556, 1.875992, -0.969256, -0.498535,-1.537150, 3.240479};
    Mat matrixMat = Mat(1, 9, CV_32FC1, matrix).t();
    cv::gpu::GpuMat gpuMatrixMat;
    gpuMatrixMat.upload(matrixMat);

    float matrixDest[9] = {1,1,1,1,1,1,1,1,1};
    Mat matrixDestMat = Mat(1, 9, CV_32FC1, matrixDest).t();
    cv::gpu::GpuMat destMatrixMat;
    destMatrixMat.upload(matrixDestMat);

    cv::gpu::GpuMat nextMat;
    cv::gpu::gemm(gpuMatrixMat, destMatrixMat, 1, cv::gpu::GpuMat(), 0, nextMat);

    return 0;
};
</code></pre>

<p>and the error I receive is:</p>

<pre><code>OpenCV Error: Assertion failed (src1Size.width == src2Size.height) in gemm, file /Users/myuser/opencv-2.4.12/modules/gpu/src/arithm.cpp, line 109
libc++abi.dylib: terminating with uncaught exception of type cv::Exception: /Users/myuser/opencv-2.4.12/modules/gpu/src/arithm.cpp:109: error: (-215) src1Size.width == src2Size.height in function gemm
</code></pre>

<p>Now how can the src1Size.width be equal to src2Size.height? The width and height are different.</p>