title: openCV vs GIMP, edge detection fails in openCV
body: <p>I am doing Sobel edge detection in openCV using the with following parameters:</p>
  
  <pre><code>cv.Sobel(mat, edgemat, 1, 1)
  # mat -&gt; source image
  # edgemat -&gt; taget output image 
  # 1 -&gt; xorder (int) – Order of the derivative x
  # 1 -&gt; yorder (int) – Order of the derivative y
  # apertureSize (int) – Size of the extended Sobel kernel -&gt; its by default set to 3
  </code></pre>
  
  <p>I also did the Sobel edge detection on the image using GIMP.</p>
  
  <p>The source image is: <img src="https://i.stack.imgur.com/ugN6W.png" alt="Source image">
  The output by openCV is <img src="https://i.stack.imgur.com/QlVZk.png" alt="openCV output">
  The output by GIMP is <img src="https://i.stack.imgur.com/QU41s.png" alt="GIMP output"></p>
  
  <p>Why such a big difference between the outputs by openCV and GIMP. The quality of output by GIMP surpasses openCV by light years.</p>