title: Fill the outside of contours OpenCV
body: <p>I am trying to color in black the outside region of a contours using openCV and python language.
  Here is my code :</p>
  
  <pre><code>contours, hierarchy = cv2.findContours(copy.deepcopy(img_copy),cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
  areas = [cv2.contourArea(c) for c in contours]
  max_index = np.argmax(areas)
  cnt=contours[max_index]
  # how to fill of black the outside of the contours cnt please? `
  </code></pre>