title: SIFT descriptors values: OpenCV vs VLFeat
body: <p>I'm trying to compare the SIFT implementation of <a href="http://docs.opencv.org/3.1.0/da/df5/tutorial_py_sift_intro.html" rel="nofollow noreferrer">OpenCV</a> and <a href="http://www.vlfeat.org/overview/sift.html" rel="nofollow noreferrer">VLFeat</a>. </p>
  
  <p>I noticed that the descriptors value for VLFeat are integers, such as:</p>
  
  <p><code>0 0 0 0 0 0 0 0 0 0 0 17 45 20 26 0 1 ...</code></p>
  
  <p>While for OpenCV:</p>
  
  <p><code>0.0391555 0 0 0.0998274 0.235747 0 0 0.0276871 0.156622 ...</code></p>
  
  <p>Notice that these are descriptors for 2 different images.</p>
  
  <p>I have two questions:</p>
  
  <ol>
  <li>Why they have two different values? </li>
  <li>If I'm going to need the OpenCV representation for k-means using VLFeat (and then VLAD encoding) do I need to change these values?</li>
  </ol>