title: Range of output values in calcOpticalFlowFarneback function in Python OpenCV
body: <p>I am calculating the optical flow for a video using</p>
  
  <pre><code>flow = cv2.calcOpticalFlowFarneback(prvs,next, None, 0.5, 3, 15, 3, 5, 1.2, 0)
  </code></pre>
  
  <p>The input resolution is 320x240. I computed some basic stats for the flow data received from the function with this code</p>
  
  <pre><code>arr1 = np.load(file_path)
  y = arr1[:,:,0]
  x = arr1[:,:,1]
  
  if (y_min &gt; y.min()):
      y_min = y.min()
  
  if (y_max &lt; y.max()):
      y_max = y.max()
  </code></pre>
  
  <p>and I got the following values:</p>
  
  <pre><code>y:
  
      min                max                mean                std_dev
  -838.59191895        850.21942139        0.01124349        4.41635523
  
  
  
  x:
  
      min                max                mean                std_dev
  -58.26990128        73.48989105        0.00110086        2.47226620
  </code></pre>
  
  <p>I noticed that for <code>y</code> coordinates the min and max values far exceed the input dimensions, i.e., <code>320x240</code>. Can anybody point out the reason for this observation? I'm unable to figure out the valid range of values expected from the <code>cv2.calcOpticalFlowFarneback</code> function.</p>