OpenCV Assertion failed: (-215:Assertion failed) npoints >= 0 && (depth == CV_32F || depth == CV_32S)

Question

I have found the following code on this website:

import os
import os.path
import cv2
import glob
import imutils
CAPTCHA_IMAGE_FOLDER = \"generated_captcha_im         


        

Answer 1

This is doing the wrong thing:

contours = contours[0] if imutils.is_cv2() else contours[1]

imutils.is_cv2() is returning False even though it should return True. If you don't mind to remove this dependency, change to:

contours = contours[0]

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I found out the reason. Probably, the tutorial you are following was published before OpenCV 4 was released. OpenCV 3 changed cv2.findContours(...) to return image, contours, hierarchy, while OpenCV 2's cv2.findContours(...) and OpenCV 4's cv2.findContours(...) return contours, hierarchy. Therefore, before OpenCV 4, it was correct to say that if you use OpenCV 2 it should be contours[0] else contours[1]. If you still want to have this "compatibility", you can change to:

contours = contours[1] if imutils.is_cv3() else contours[0]

Answer 2

In OpenCV4, cv2.findContours has only 2 return values. Contours being the FIRST value

contours, _ = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

Note that I added underscore to let go of the other return value of hierarchy

Answer 3

【OpenCV 3 changed cv2.findContours(...) to return image, contours, hierarchy】 This content is very helpful for me. I adda new variable to the front and I fix all the error..

Answer 4

I wrote the same code in following way:

_, contours, hierarchy = cv2.findContours(img,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)

and my code worked. I think previously it was returning 2 variables now we have to unpack into three variables. If this doesn't work try the following:

_, contours, _ = cv2.findContours(img,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)

this should work.

For more information, you can visit the OpenCV documentation page: https://docs.opencv.org/3.1.0/d4/d73/tutorial_py_contours_begin.html

I hope this will help you.

Answer 5

 (x, y, w, h) = cv2.boundingRect(contour.astype(np.int))

Answer 6

This is because of opencv-python version 4.0.0. If you want to fix this without changing your code then downgrade opencv-python to version 3.4.9.31

• Uninstall opencv-python

  pip uninstall opencv-python

• Install opencv-python==3.4.9.31

  pip install opencv-python==3.4.9.31

If facing issue with function 'pointSetBoundingRect', you need to install 'opencv-python-headless'

pip install opencv-python-headless==3.4.9.31