title: OpenCV smoothen corners of a drawn polygon
body: <p>I draw this mask with <code>cv2.drawContours</code>. I need edges to be round. How should I do it?</p>
  <p><a href="https://i.stack.imgur.com/maRLW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/maRLW.png" alt="mask" /></a></p>