Dear all,
I am constantly running into problems using convexityDefects(). I have created an example image (see below), and OpenCV correctly finds all contours and convex hulls, but still, when running the line of code I commented out it throws the error
error: (-215:Assertion failed) hpoints > 0 in function 'cv::convexityDefects'
Where is the error? Is it related to the image depth?
import cv2
import imutils
import numpy as np
black = np.zeros((500,500), dtype=np.uint8)
cv2.rectangle(black, (60,60), (440, 440), (255,255,255), 4)
poly = np.array([[80,80], [110, 110], [80, 200], [300, 110]])
cv2.drawContours(black, [poly], 0, (255, 255, 255), 3)
cnts = cv2.findContours(black, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
cnts = imutils.grab_contours(cnts)
for c in cnts:
toShow = cv2.cvtColor(black.copy(), cv2.COLOR_GRAY2BGR)
cv2.drawContours(toShow, [c], 0, (0,255,0), 2)
hull = cv2.convexHull(c)
cv2.drawContours(toShow, [hull], 0, (0,0,255), 1)
# print("conv defects", cv2.convexityDefects(c, hull))
cv2.imshow("cont", toShow)
cv2.waitKey()
test image
inner contour with correct convex hull