title: OpenCV FREAK returns too many outliers
body: <p>I am trying the quite new descriptor FREAK from the latest version of OpenCV following the <strong>freak_demo.cpp</strong> <a href="https://github.com/kikohs/freak/blob/master/demo/freak_demo.cpp">example</a>. Instead of using SURF I use FAST. My basic code is something like this:</p>
  
  <pre><code>std::vector&lt;KeyPoint&gt; keypointsA, keypointsB;
  Mat descriptorsA, descriptorsB;
  std::vector&lt;DMatch&gt; matches;
  
  FREAK extractor;
  BruteForceMatcher&lt;Hamming&gt; matcher;
  
  FAST(imgA,keypointsA,100);
  FAST(imgB,keypointsB,20);
  
  extractor.compute( imgA, keypointsA, descriptorsA );
  extractor.compute( imgB, keypointsB, descriptorsB );
  
  matcher.match(descriptorsA, descriptorsB, matches);
  </code></pre>
  
  <ul>
  <li>The algorithm finds a lot of matches, but there are a lot of outliers. Am I doing things right? Is there a way for tuning the algorithm?</li>
  </ul>