title: ORB is not detecting keyPoints in opencv 2.4.9
body: <p>I'm trying to detect keypoints with ORB everything is fine until I switched to Opencv 2.4.9.</p>
  
  <p>Firts, it seems that the number of keys decresed, and for some images, no keypoints are detected : </p>
  
  <p>This is my code compiled with two version : (2.3.1 and 2.4.9)</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;opencv2/opencv.hpp&gt;
  #include &lt;opencv2/features2d/features2d.hpp&gt;
  
  
  using namespace cv;
  
  
  int main(int argc, char **argv){
  
    Mat img = imread(argv[1]);
  
    std::vector&lt;KeyPoint&gt; kp;
  
    OrbFeatureDetector detector;
    detector.detect(img, kp);
    std::cout &lt;&lt; "Found " &lt;&lt; kp.size() &lt;&lt; " Keypoints " &lt;&lt; std::endl;
  
    Mat out;
    drawKeypoints(img, kp, out, Scalar::all(255));
  
    imshow("Kpts", out);
  
    waitKey(0);
    return 0;
  }
  </code></pre>
  
  <p>Result : 
  2.3.1 :
  Found 152 Keypoints</p>
  
  <p><img src="https://i.stack.imgur.com/ZLWF1.png" alt="kp detected"></p>
  
  <p>2.4.9 :
  Found 0 Keypoints</p>
  
  <p><img src="https://i.stack.imgur.com/GSXRX.png" alt="zero kpts"></p>
  
  <p>I also tested with a different ORB Constructor, but I get the same result, no KPts.
  The same constuctor values as in 2.3.1 default's constructor :
  2.4.9 custom constr :</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;opencv2/opencv.hpp&gt;
  #include &lt;opencv2/features2d/features2d.hpp&gt;
  
  
  using namespace cv;
  
  
  int main(int argc, char **argv){
  
    Mat img = imread(argv[1]);
  
    std::vector&lt;KeyPoint&gt; kp;
  
    // default in 2.4.9 is : ORB(700, 1.2f, 3, 31, 0);
    OrbFeatureDetector detector(500, 1.2f, 8, 31, 0); // default values of 2.3.1
    detector.detect(img, kp);
    std::cout &lt;&lt; "Found " &lt;&lt; kp.size() &lt;&lt; " Keypoints " &lt;&lt; std::endl;
    Mat out;
    drawKeypoints(img, kp, out, Scalar::all(255));
  
    imshow("Kpts", out);
  
    waitKey(0);
    return 0;
  }
  </code></pre>
  
  <p>Do you have any idea what's happening ? And how can I fix it ?</p>
  
  <p>Thank you.</p>