Opencv Python: How To Detect If A Window Is Closed?

I have the following code: total_frames = 50 cv2.cv.NamedWindow('Dragonfly Simulation') cv2.cv.StartWindowThread() for i in range(total_frames): # do stuff img_name = # som

Solution 1:

I was just looking for a way to detect when the window has been closed using the X button of the window in addition to waiting for a key press, but I couldn't find an answer anywhere (IsWindowVisible and cvGetWindowHandle are not available in the Python cv2 module).

So I played around and this is how it works:

while cv2.getWindowProperty('window-name', 0) >= 0:
    keyCode = cv2.waitKey(50)
    # ...

cv2.getWindowProperty() returns -1 as soon as the window is closed.

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For explanation, see the documentation for the enumeration of cv::WindowPropertyFlags: getting the flag with index 0 is the fullscreen property, but actually it doesn't matter which flag to use, they all become -1 as soon as the window is closed.

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Note: This might only work for certain GUI backends. Notably, it will not work with the GTK backend used in Debian/Ubuntu packages. To use the Qt backend instead, you have to install opencv-python via pip.

Solution 2:

As of version 2.2 there is a simple solution (this is modified from the loop in hist.py):

    cv2.imshow('image',im)
    whileTrue:
        k = cv2.waitKey(100) # change the value from the original 0 (wait forever) to something appropriate
...
        elif k == 27:
            print('ESC')
            cv2.destroyAllWindows()
            breakif cv2.getWindowProperty('image',cv2.WND_PROP_VISIBLE) < 1:        
            break        
    cv2.destroyAllWindows()

Solution 3:

I tested on C++ using the getWindowProperty('image', WND_PROP_VISIBLE), but it does not work. So I used the WND_PROP_AUTOSIZE and it works.

I did like this:

cv::namedWindow("myTitle", WINDOW_AUTOSIZE);

while(1)
{
    cv::imshow("myTitle", myImage);


    if (cv::getWindowProperty("myTitle", WND_PROP_AUTOSIZE) == -1)
        break;
}

Solution 4:

if cv2.getWindowProperty('windowname',1) == -1 :
            break
        cv2.imshow('windowname', image)

Solution 5:

import cv2
import numpy as np

# total_frames = 50
cv2.namedWindow("Dragonfly Simulation")
cv2.startWindowThread()
# for i in range(total_frames):whileTrue:
    # do stuff
    img = np.random.randint(0,255,(200,300)).astype(np.uint8)
    cv2.imshow("Dragonfly Simulation", img)
    key = cv2.waitKey(200)
    print key
    if key in [ord('a'), 1048673]:
        print'a pressed!'elif key in [27, 1048603]: # ESC key to abort, close window
        cv2.destroyAllWindows()
        break# do the rest of processing after break print'results:'

Sure, you can check user inputs using waitKey and here is a small example based on your code. I changed old cv interface to cv2. I think cv is obsolete.

(Edit) I moved cv2.destroyAllWindows() to inside the while loop to make it clear that the window closes when the user pressed ESC key (which you can assign a key of your choice). I do not think opencv has a proper event handler to catch the window close event like in other GUI toolkit (wxPython etc). So you will need to define how your users should close the window and watch out for that.