Opencv imshow() freezes when updating

Question

For my image processing algorithm I\'m using python / OpenCV. The output of my algorithm shall be updated im the same window over and over again.

However sometimes

Answer 1

I have the very same issue and I noticed that the fps the window is updated is getting slower and slower until it freezes completely. Increasing the waitKey(x) to something higher just extends the duration where the images are updated but when the time that cv2.imshow() needs to calculate exceeds the time from wait(Key) it just stops updating.

(Skip this complainment:) I think the cv2.imshow() with waitKey() combination is a complete design error, why isn't imshow() just blocking until the UI is updated? That would make life so much easier without having to call waitKey() everytime...

P.S.: There is a possibility to start an own thread for opencv windows inside opencv:

import cv2
img = cv2.imread("image.jpg")
cv2.startWindowThread()
cv2.namedWindow("preview")
cv2.imshow("preview", img)

source: cv2.imshow command doesn't work properly in opencv-python

Well this doesn't work for me because I always get this errors when I run it:

(python3:1177): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Attempt to unlock mutex that was not locked
Aborted

Maybe you could try it and report if it is working for you?

Edit: Okay I solved the problem for me by creating a separate script imshow.py:

import cv2
import os.path

while True:
    if os.path.exists("image.pgm"):
        image = cv2.imread("image.pgm")
        if not image is None and len(image) > 0:
            cv2.imshow("Frame", image)
            cv2.waitKey(20)

And I am writing the image out in my other program with: cv2.imwrite("image.pgm", image) And I am calling the script like this:

import subprocess
subprocess.Popen(["python3", "imshow.py"])

Although this is creating some dirty reads sometimes it is sufficient enough for me, a better solution would be to use pipes or queues between the two processes.