title: OpenCV low framerate with ORB detector
body: <p>I was playing with OpenCV <code>Mixed Processing</code> tutorial and I experienced a good framerate (~27) when detecting features in camera frames with FAST detector.</p>
  
  <p>I changed the detector to ORB and the framerate dropped to around 10. Is this because ORB is not as fast as FAST or I'm missing something? </p>
  
  <pre><code>Mat&amp; mGr  = *(Mat*)addrGray;
  vector&lt;KeyPoint&gt; v;
  
  OrbFeatureDetector detector(50); 
  // FastFeatureDetector detector(50);
  detector.detect(mGr, v);
  </code></pre>
  
  <ul>
  <li>Is there any way to tune up ORB and speed this up?</li>
  <li>Is it possible to do the detection in, let's say, every 5 frames?</li>
  </ul>