How do i prevent a segmentation fault with opencv in python

Question

I am trying to re-produce a simple code using opencv with python 3.9.7 on ArchLinux using gnome as a desktop environment. I installed opencv with the command pip3 install --upgrade opencv-python. My current code is shown below.

import cv2
cap = cv2.VideoCapture(0)
cap.set(3, 640)
cap.set(4, 480)

while True:
    success, img = cap.read()
    cv2.imshow("Video", img)  # This is where the code fails
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

The code runs if I remove everything below the imshow() command, but when I add that single line, the execution fails with the following error

Segmentation fault (core dumped)

It appears that a number of people have had this issue, but I have not seen a resolution. Does anyone know how I can fix this?

you must error-check creation of VideoCapture and result of cap.read. all the code examples show how to do that. it's not optional. work with docs.opencv.org. -- and don't use magic numbers in the set() calls. use cv2.CAP_PROP_FRAME_WIDTH and height — Christoph Rackwitz
– Christoph Rackwitz, Commented Nov 6, 2021 at 21:29
If you're getting a segfault in Python, then it's very likely the problem is in the underlying library, not in your code. Possibly some incompatibilities in what I assume is a pre-built package you're installing. In your place, I'd probably try to make my own build of OpenCV, and see if that works better. — Dan Mašek
– Dan Mašek, Commented Nov 6, 2021 at 23:51
@ChristophRackwitz Yeah, totally agree. This code snippet looks familiar enough, although I'm not sure where people are copying this crap from, without giving it a single though. | Still, it shouldn't cause a segfault. — Dan Mašek
– Dan Mašek, Commented Nov 6, 2021 at 23:55
@DanMašek I would not say that I merely copied the example without thought. I did visit the docs, but only found examples in C++ and I was not sure how applicable they were to the python syntax. I have to know that something exists to know I should go looking for it. That said, I found the error. It appears that every version of opencv-python beyond 4.5.3.56 has presented this issue for Linux users and MacOS users. I downgraded my opencv-python library and everything works now. And I did find a python example with the error checking you mentioned and will use that in the future. — Jon
– Jon, Commented Nov 7, 2021 at 1:43

Jon · Accepted Answer · 2021-11-07 01:45:10Z

8

After some digging I found that this is an issue for MacOS and Linux users for versions of opencv-python beyond 4.5.3.56. I downgraded my opencv-python library 20 4.5.3.56 and now everything works properly.

answered Nov 7, 2021 at 1:45

Jon

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2 Comments

mcy Over a year ago

Having the same issue with wsl arch, may I ask where you have found this information?

PYK Over a year ago

In my case, it worked with: pip install opencv-python==3.4.10.35

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