python OpenCV Segmentation fault (core dumped)

Question

I'm coding in python and using my webcam for now on testing.

(ASUS KV55J | Ubuntu 14.04 | python 2.7.6 (default, Jun 22 2015, 17:58:13) [GCC 4.8.2] | OpenCV version '2.4.8')

I can successfully show the image from my webcam (very simple code) but when I try to set a mouse callback to when mouse passes over the image (also a very simple code) there are a big issue, a Segmentation fault after several frames (takes about 10/20seconds to fail but if i comment the callback it will work until "Ctrl-c" pressed).

Does anyone know why it happens?

I ran this and got this error (even if i dont move the mouse or press anything):

ncc@ncc-K55VJ:~/Desktop/testes_python/gui$ python a_teste_capture.py 
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
VIDIOC_QUERYMENU: Invalid argument
Left mouse button pushed
Left mouse button pushed
Left mouse button pushed
Left mouse button pushed
Left mouse button pushed
Segmentation fault (core dumped)

The simplest code I had at the beggining was:

import cv, cv2

def click_and_take_frame(event, x, y, flags, param):

    if event == cv2.EVENT_LBUTTONDOWN:
        print 'Left mouse button pushed'


def main_function():
    camera_device=cv2.VideoCapture(0)
    frame_name="Segmentation fault (core dumped) TEST WINDOW"
    cv2.namedWindow(frame_name, cv2.WINDOW_AUTOSIZE)

    while 1:
        (grabbed1, frame1) = camera_device.read()
        frame1= cv2.cvtColor(frame1, cv2.CV_8U)
        cv2.imshow(frame_name, frame1)
        cv2.setMouseCallback(frame_name, click_and_take_frame)
        key = cv2.waitKey(1) & 0xFF

    cv2.destroyAllWindows()        # Closes displayed windows


if __name__ == '__main__':
    import sys

    main_function()

I can't reproduce the segfault when I run your code on OS X. It seems to work fine on that platform. — Aurelius
– Aurelius, Commented Jun 22, 2016 at 22:48

Cybersupernova · Accepted Answer · 2017-12-22 09:25:38Z

1

According to my past experience this error occurs when you overload machine resources.

In your case there are two things which can do this

while 1 is a infinite loop even if there is no frame. You can correct this by moving (grabbed1, frame1) = camera_device.read() outside while loop and use while grabbed1: which will only run the loop if frame is True. You can read more about this here.
Your click listener is inside a infinite loop. There is no point to place listeners inside a loop. You can move cv2.setMouseCallback(frame_name, click_and_take_frame) above while loop and you will stop wasting resources.

answered Dec 22, 2017 at 9:25

Cybersupernova

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