title: Detect edge from binary image using Canny edge detection from OpenCV
body: <p>I'm trying to extract the contour of some traffic signs. The images pass through several steps in order to get a good segmented image. In the final step before applying Canny method I get this image:</p>
  
  <p><a href="https://i.stack.imgur.com/Rb5nd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Rb5nd.png" alt="enter image description here"></a></p>
  
  <p>After applying Canny I get this image:</p>
  
  <p><a href="https://i.stack.imgur.com/irY0F.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/irY0F.png" alt="enter image description here"></a></p>
  
  <p>The algorithm performs as expected except the top left image for which returns an open contour. 
  So, my question is, is there any way to use Canny in a manner that the top left image returns an closed contour?</p>