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 the window freezes and doesn't update at all, but the algorithm is still running and updated the picture a multiple times in the meantime. The window turns dark gray on this Ubuntu machine.

Here is an excerpt of the involved code:

for i in range(0,1000):
    img = loadNextImg()
    procImg = processImg(img)
    cv2.imshow("The result", procImg)
    cv2.waitKey(1)

N.B.: processImg() takes about 1-2 s for its procedures. The line cv2.imshow(procImg) creates the window in first instance (i.e. there is no preceding invocation)

Answer 1

My suggestion is to use Matplotlib pyplot for displaying the image. I do it the following way.

import matplotlib.pyplot as plt
# load image using cv2....and do processing.
plt.imshow(cv2.cvtColor(image, cv2.BGR2RGB))
# as opencv loads in BGR format by default, we want to show it in RGB.
plt.show()

I know it does not solve the problem of cv2.imshow, but it solves our problem.

Answer 2

Increasing the wait time solves this issue. However in my opinion this is unnecessary time spent on sleeping (20 ms / frame), even though it's not much.

Changing

cv2.waitKey(1)

to

cv2.waitKey(20)

prevents the window from freezing in my case. The duration of this required waiting time may vary on different machines.