title: OpenCV HOG Descriptor Parameters
body: <p>I am trying to detect people from a camera's feed using <a href="http://docs.opencv.org/2.4/modules/gpu/doc/object_detection.html#gpu-hogdescriptor" rel="nofollow noreferrer"><code>cv2.HOGDescriptor()</code></a> and using their default people classifier.</p>
  
  <p>The recognizer <em>kinda</em> works but I honestly am having an issue with understanding what values to assign to <code>winStride</code>, <code>padding</code>,<code>scale</code> and <code>groupThreshold</code> respectively.</p>
  
  <p>Currently, the camera feed's frame size is <em>1280 X 720</em> and I resize it to <em>400 X 400</em> then perform <code>detectMultiScale</code> with parameters</p>
  
  <pre><code>hogParams = {'winStride': (8, 8), 'padding': (32, 32), 'scale': 1.05, 'finalThreshold': 2}
  </code></pre>
  
  <p>Based off of this <a href="https://stackoverflow.com/a/26611534/4962554">answer</a>, I understand what these parameters do and represent.</p>
  
  <p>My question is, is there a way of mapping image size with these values?  A mathematical equation? An estimation method? I am not necessarily asking for a concrete or even a method that gives all values, but something better than <em>trial and error</em> or <em>magic numbers</em>.</p>
  
  <p>Most of the references and tutorials pretty much use <em>magic numbers</em> without giving a proposition of how they attained them.</p>
  
  <p><strong>PS: Here's a visual aid in case you're still not sure of my question</strong>
  <a href="https://i.stack.imgur.com/QDATu.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QDATu.jpg" alt="I am looking for the cloud"></a></p>