Display the webcam in Python using OpenCV (cv2)

webcam-cv2.py

"""
Simply display the contents of the webcam with optional mirroring using OpenCV 
via the new Pythonic cv2 interface.  Press <esc> to quit.
"""

import cv2


def show_webcam(mirror=False):
    cam = cv2.VideoCapture(0)
    while True:
        ret_val, img = cam.read()
        if mirror: 
            img = cv2.flip(img, 1)
        cv2.imshow('my webcam', img)
        if cv2.waitKey(1) == 27: 
            break  # esc to quit
    cv2.destroyAllWindows()


def main():
    show_webcam(mirror=True)


if __name__ == '__main__':
    main()

@yaswanth789 @Anupama-S-D @thetabor
This just means the frame given to imshow() is empty. So either your webcam is not detected by your computer, either the webcam index is not correct. You can try different webcam indexes, for example by changing cam = cv2.VideoCapture(0) to cam = cv2.VideoCapture(1).
Under linux you can see webcam entries with this command :
» ls /dev/ | grep video
video0 video1
This means I have two webcams entries, with index 0 and 1.

You can also find more answers here : https://stackoverflow.com/questions/27953069/opencv-error-215size-width0-size-height0-in-function-imshow

hi,@taylor D.Edmiston @Nicolas1203
does any of you know how to set the window's size (e.g. width&height) along this posted code? I am not familiat with cv2 SDK, please help!
And, does anyone how to make up this code into an online webapp just over local network?
Huge appreciate it in advance!

Hi @Guohao91,
you could do something like this

def show_webcam(mirror=False, width=600, height=600):
    cam = cv2.VideoCapture(0)
    while True:
        ret_val, img = cam.read()
        if mirror: 
            img = cv2.flip(img, 1)
        cv2.imshow('my webcam', img)
        cv2.namedWindow('my webcam',cv2.WINDOW_NORMAL)
        cv2.resizeWindow('my webcam', width, height)
        if cv2.waitKey(1) == 27: 
            break  # esc to quit
    cv2.destroyAllWindows()

Hope this helps.

@Nicolas1203
Thanks Prof.!

Please explain the 12th line. I think I'm having a problem with the syntax. How are we using 2 variables (ret_val and image) as output of read() function. Please help

Please explain the 12th line. I think I'm having a problem with the syntax. How are we using 2 variables (ret_val and image) as output of read() function. Please help

that function returns a tuple which contains two elements and python can work with multiple assignment (just try, well, a, b = 1, 2)

/usr/local/lib/python3.6/dist-packages/google/colab/patches/init.py in cv2_imshow(a)
20 image.
21 """
---> 22 a = a.clip(0, 255).astype('uint8')
23 # cv2 stores colors as BGR; convert to RGB
24 if a.ndim == 3:

AttributeError: 'NoneType' object has no attribute 'clip'
How to fix this error?

I tried running this in Pycharm and I got qt.qpa.plugin: Could not find the Qt platform plugin "cocoa" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

but then I just ran it in the terminal and It worked perfectly so incase anybody else gets that error, try that.

@m-namitha if you are trying to run the script on Google Colab which I'm guessing you are, it won't work and google says that loud and clear. They instead suggest you to use the code snippet provided by colab itself to run such scripts.

explain this man!!!

I know it's kinda late but:

"""
Simply display the contents of the webcam with optional mirroring using OpenCV 
via the new Pythonic cv2 interface.  Press <esc> to quit. 
"""

import cv2


def show_webcam(mirror=False):
    int n = 0 
# use the device /dev/video{n} in this case /dev/video0 
# On windows use the first connected camera in the device tree
    cam = cv2.VideoCapture(n)
    while True:
# read what the camera the images which are comming from the camera
# ret_val idk atm
        ret_val, img = cam.read()
# if mirror is true do flip the image 
        if mirror: 
            img = cv2.flip(img, 1)
# show the image with the title my webcam in a window
        cv2.imshow('my webcam', img)
# if you press ESC break out of the while loop and destroy all windows == free resources <3
        if cv2.waitKey(1) == 27: 
            break  # esc to quit
    cv2.destroyAllWindows()


def main():
    show_webcam(mirror=True)


if __name__ == '__main__':
    main()