Python opencv drawContours does not show anything

Question

I followed the tutorial at this page but nothing seems to happen when the line cv2.drawContours(im,contours,-1,(0,255,0),3) is executed. I was expecting to see

Answer 1

I had the same issue. I believe the issue is that the underlying image is 1-channel rather than 3-channel. Therefore, you need to set the color so it's nonzero in the first element (e.g. (255,0,0)).