CODEWITHSUNDEEP
pythonc++python-3.xopencvubuntu
KittenMittons
KittenMittons

Reputation: 73

cv2.waitKey(0) not waiting when random key pressed - OpenCV 3.1.0, Python3, Ubuntu

So I've got a program where I assign different keypresses to different functions. I'm using cv2.waitKey(0) to go through frames one by one. However, when a key that isn't assigned a function is pressed, the next frame is still loaded. How do I prevent a non-assigned keypress from loading the next frame in my loop?

Thanks!

while (cap.isOpened()):
frameclick = cv2.waitKey(0)
ret, frame = cap.read()
cv2.imshow('frame',frame)

if frameclick == ord('a'):
    swingTag()

elif frameclick == ord('r'):
    rewindFrames()

elif frameclick == ord('s'):
    stanceTag()

elif frameclick == ord('d'):
    unsureTag()

elif frameclick == ord('q'):
    with open((selectedvideostring + '.txt'), 'w') as textfile:
        for item in framevalues:
            textfile.write("{}\n".format(item))
    break

Upvotes: 1

Views: 1392

Answers (2)

Quang Hoang
Quang Hoang

Reputation: 150825

As mentioned in @Ervin's answer, try:

while (cap.isOpened()):
    ret, frame = cap.read()

    # check if read frame was successful
    if ret == False: break;

    # show frame first
    cv2.imshow('frame',frame)

    # then waitKey -- and make it <= 255
    frameclick = cv2.waitKey(0) & 0xFF

    if frameclick == ord('a'):
        swingTag()

    elif frameclick == ord('r'):
        rewindFrames()

    elif frameclick == ord('s'):
        stanceTag()

    elif frameclick == ord('d'):
        unsureTag()

    elif frameclick == ord('q'):
        with open((selectedvideostring + '.txt'), 'w') as textfile:
            for item in framevalues:
                textfile.write("{}\n".format(item))
        break

Upvotes: 0

Ervin Szilagyi
Ervin Szilagyi

Reputation: 16815

The problem is with your logic. Your program enters into the the while loop and waits for a key. Then, if a key is pressed, the next frame is read, but at the moment your program does not care which key was pressed. So, you have your next frame and only then you check which button was pushed, which is to late.

Upvotes: 1

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