gpu::warpPerspective and warpPerspective return different mats

asked 2015-06-08 22:56:54 -0500

Hi all

I have a very basic question - I am new to OpenCV and CV in general.

This question is related to OpenCV 2.4. I am currently using the github version of OpenCV with the following tag: remotes/origin/2.4

found at: https://github.com/Itseez/opencv

I am doing experiments on Nvidia GPUs with the CUDA support and calling the warpPerspective function offered for the host and the GPU. Even if I am passing warpPerspective the very same input (properly transferred to GPU memory when needed) I obtain different results. My experiments are on an Intel box with a K20Xm GPU.

Here is a code snippet representing what I am doing:

// declare maskin and maskout and fill maskin up

Mat maskin ...; Mat maskout ...;

// transfer input to gpu

gpu::GpuMat maskin_gpu; maskin_gpu.upload (maskin);

// allocate output on GPU and corresponding CPU version for checking

gpu::GpuMat maskout_gpu (maskout.size (), maskout.type ()); Mat maskout_check (maskout.size(), maskout.type());

gpu::warpPerspective (maskin_gpu, maskout_gpu, myH, size);

// transfer back GPU-->HOST the result into maskout_check

maskout_gpu.download (maskout_check);

// now do same calculation on CPU

warpPerspective (maskin, maskout, myH, size);

// check results

Mat diffMask = maskout != maskout_check; int numNoZero = cv::countNonZero(diffMask); if (numNoZero > 0) { printf ("Drats..\n"); }

Printing the number of non-zeros gives me about ~2000 mismatches for 720x480 Mats based on CV_8U elements.

What is it that I am doing wrong? Is this supposed to happen because of re-ordering of operations in the GPU code?

Thanks!!

-- Carlo

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