I think I have found a bug in this tutorial. It is focussed in this part:
def draw(img, corners, imgpts):
corner = tuple(corners[0].ravel())
img = cv2.line(img, corner, tuple(imgpts[0].ravel()), (255,0,0), 5)
img = cv2.line(img, corner, tuple(imgpts[1].ravel()), (0,255,0), 5)
img = cv2.line(img, corner, tuple(imgpts[2].ravel()), (0,0,255), 5)
return img
because cv2.line() return none, img will be nonetype. So the correct way should be:
def draw(img, corners, imgpts):
corner = tuple(corners[0].ravel())
cv2.line(img, corner, tuple(imgpts[0].ravel()), (255,0,0), 5)
cv2.line(img, corner, tuple(imgpts[1].ravel()), (0,255,0), 5)
cv2.line(img, corner, tuple(imgpts[2].ravel()), (0,0,255), 5)
return img
