title: How to properly detect corners using Harris detector with OpenCV?
body: <p>I'm testing some image processing to obtain <strong><em>minutiae</em></strong> from digital fingerprints. I'm doing so far:</p>
  
  <ol>
  <li>Equalize histogram</li>
  <li>Binarize</li>
  <li>Apply Zhang-Suen algorithm for lines thinning (this is not working properly).</li>
  <li>Try to determine corners in thinned image and show them.</li>
  </ol>
  
  <p>So, the modifications I'm obtaining are:</p>
  
  <p><img src="https://i.stack.imgur.com/3zrLjt.png" alt="enter image description here">
  <img src="https://i.stack.imgur.com/xBM0Jt.png" alt="enter image description here">
  <img src="https://i.stack.imgur.com/HNa48t.png" alt="enter image description here">
  <img src="https://i.stack.imgur.com/bacB3t.png" alt="enter image description here"></p>
  
  <p>However, I can't get to obtain possible corners in the last image, which belongs to <code>thinned</code> instance of <code>Mat</code> object.</p>
  
  <p>This is code for trying to get corners:</p>
  
  <pre><code>corners_image = cornerHarris(thinned,1,1,0.04)
  corners_image = dilate(corners_image,None)
  </code></pre>
  
  <p>But trying <code>imshow</code> on the resulting matrix will show something like:</p>
  
  <p><img src="https://i.stack.imgur.com/wEl2z.png" alt="enter image description here"></p>
  
  <p>a <strong>black image</strong>. </p>
  
  <p>How should I determine corners then?</p>