title: How could I implement a centered shear an image with opencv
body: <p>When I use warpAffine to shear an image:  </p>
  
  <pre><code>M2 = np.float32([[1, 0, 0], [0.2, 1, 0]])
  aff2 = cv2.warpAffine(im, M2, (W, H))
  </code></pre>
  
  <p>I obtain an image that is not sheared around the image center. I can see black triangular areas on one side of the image, and the other side does not have black areas. </p>
  
  <p>How could I let the image be sheared symmetricly ?</p>