autobuffer too large in calcSIFTDescriptor (sift.cpp) L552 (Bug #3282)

Hi,
I've run in a bug in the SIFT descriptor implementation. The code to recreate the error is at the end of this message. I would gladly edit the code myself and submit the correction if someone can walk me through it.

So the bug happens whenever a keypoint with a size too large is given. If this is the case, a std::bad_alloc nomem exception is raised during the descriptor extraction. This happens in the file sift.cpp, at the calcSIFTDescriptor function, line 552. The size requested for the autobuffer is too large. It correspond to the width of the histogram created to accumulate the sift gradient vectors. I would suggest to clip the radius to prevent the creation of a buffer too large: clip the radius to the diagonal of the image. For example add a line after L545 :

int radius = cvRound(hist_width * 1.4142135623730951f * (d + 1) * 0.5f); //L545
radius = radius>sqrt(img.cols*img.cols + img.rows*img.rows) ? sqrt(img.cols*img.cols + img.rows*img.rows):radius; //new line

This code will create the error. If the error dont happen, you have more memory than me, increase the size of the keypoint.

cv::initModule_nonfree();
vector<KeyPoint> kp;
Mat descriptors;
kp.push_back(KeyPoint(10,10,650,-1)); //650 is the size
Mat img(1280,720,CV_8U);
Ptr<DescriptorExtractor> descriptor = DescriptorExtractor::create("SIFT");
descriptor->compute(img, kp, descriptors);