OpenCV 2.4.0, cv::gpu::PyrLKOpticalFlow::sparse - make program crash when modifying the search window size (Bug #1823)

Hello all,

First of all, thanks a lot for your great job. I am using OpenCV for quite a bit now, and it is more and more amazing. Thank you again.

I was eager to try the new optical flows functions implemented on gpu. The goal was to compare the performances between OpenCV Alone functions, OpenCV compiled with CUDA functions (here i am working with CUDA 4.1) and the same functions implemented with IPP.
That is why i tried to test gpu::PyrLKOpticalFlow::sparse.

For one of my current problem, i am using a sparse optical flow with a window size between 80 and 120 pixels.
With OpenCV Alone sparse LK Optical Flow, no problems, but the use of the gpu function makes my program crash.

By looking at the sources (pyrlk.cpp, ln 162) there is the following assertion :
CV_Assert(patch.x > 0 && patch.x < 6 && patch.y > 0 && patch.y < 6);
with
patch.x = (winSize.width * cn + block.x - 1) / block.x with block.x = 32 when winSize.width * cn > 32 (for me cn = 1)
and
patch.y = (winSize.height + block.y - 1) / block.y with block.y = 8 when winSize.width * cn > 32 (for me cn = 1)
implying then that
winSize.width < 161
and
winSize.height < 41
I assume that this patch dimensions allow to divide the images in regions in order to run gpu routines and not to be limited by the gpu maximum operation number. But why are these dimensions so different ? In my case, the problem is the size height. Is there a reason it is limited to 41 ?

Here is my pseudo code :

 1Mat grayImgA = imread("imgA.png", CV_LOAD_IMAGE_GRAYSCALE);
 2Mat grayImgB = imread("imgB.png", CV_LOAD_IMAGE_GRAYSCALE);
 3
 4gpu::GpuMat gpuGrayImgACopyROI(grayImgA);
 5gpu::GpuMat gpuGrayImgBCopyROI(grayImgB);
 6
 7int maxPtNb            = 5000;
 8float qualityLevel            = 0.01f;
 9int minimumDistance    = 4;
10
11// extract features
12gpu::GoodFeaturesToTrackDetector_GPU detector(maxPtNb, qualityLevel, minimumDistance);
13gpu::GpuMat gpuCornersA;
14
15detector(gpuGrayImgACopyROI, gpuCornersA);
16
17// sparse lk optical flow
18gpu::PyrLKOpticalFlow    d_pyrLK;
19
20d_pyrLK.winSize.width    = 45;
21d_pyrLK.winSize.height    = 45;
22d_pyrLK.maxLevel        = maxLevel;
23d_pyrLK.iters            = 20;
24d_pyrLK.derivLambda    = 0.3;
25d_pyrLK.useInitialFlow    = false;
26
27gpu::GpuMat d_nextPts;
28gpu::GpuMat d_status;
29gpu::GpuMat d_err;
30
31d_pyrLK.sparse(gpuGrayImgA, gpuGrayImgB, gpuCornersA, d_nextPts, d_status, &d_err);           // crash because of winSize.height >= 41

Thank you very much in advance for your answers and again, thank you for your great work.