How to make USB camera work with OpenCV?

Question

I copied code from https://mcmap.net/q/325821/-python-how-to-capture-image-from-webcam-on-click-using-opencv and used with default (built-in) camera, it worked. Then I attached USB camera, tested it with VLC and changed the code to open camera 1:

cam = cv2.VideoCapture(1)

I check whether the camera is open cam.isOpened() -- it is -- but the camera is not enabled (its hardware indicator, LED, is off) and indeed all I see on the screen is black frame.

Is there some extra special code to add in order to enable USB camera?

Coonhound

Are you sure the usb camera is camera 1, i've done this before and had to use cv2.VideoCapture(0) – Teeny

@Stanley, big THANK YOU! :-) I could spend no matter how much time and I wouldn't guess the numbers are shuffled after attaching USB camera. Could you please post your comment as regular answer? – Coonhound

Thank you, it's almost an "honour" for me as a self taught programmer to be able to help experienced programmers! goes to show that everyone can learn something from anyone. Again, thanks! :) – Teeny

Answer 1

Are you sure the usb camera is camera 1, i've done this before and had to use cv2.VideoCapture(0)

Teeny

Answer 2

You can also refer this link here

https://devtalk.nvidia.com/default/topic/1027250/how-to-use-usb-webcam-in-jetson-tx2-with-python-and-opencv-/

Here he changes the line below to

cap = cv2.VideoCapture("/dev/video1") # check this

Before plugging in the camera, go to your terminal home

1. Type cd /dev
2. Type ls video and then press tab, if you find only result as video0, that means only webcam is present.
3. Now repeat 1 to 2 with USB webcam plugged in. You should find video1 or video2 when you repeat the steps.

Sacchariferous

The post above specifically calls out that this is for Windows (via the tag). The path /dev/video1 is a Linux device path. This doesn't exist in the same way on Windows. – Fellmonger

Answer 3

I ran into the same problem, turns out sometimes the webcam can take both slots 0 and 1. So cam = cv2.VideoCapture(2) worked for me. This was found using the cd /dev-method above.

Gallon

Answer 4

I do not know why but on my laptop (Acer Aspire 3) the usb webcam works with python opencv only if I plug it in the right side usb of my laptop and NOT if I plug it in the left side usb. So try plugging the webcam on all the usb ports you have. (I also had to use cam = cv2.VideoCapture(2) as @Slayahh suggested.

Homochromatic

Answer 5

in accordance to the accepted answer and this https://mcmap.net/q/800294/-how-to-make-usb-camera-work-with-opencv

i realized cv2.VideoCapture(4) the parameter 4 is directly proportional to the file suffix of /dev/video4

Eure

Answer 6

In my case the LED indicator turned on, but there was read returned none. Somehow the solution was to call call cv2.VideoCapture again.

cap = cv2.VideoCapture(1)
_ = cv2.VideoCapture(1)

Casuistry

Answer 7

I just tried cv2.VideoCapture(n) with n from 0 to 4. For me worked out with cv2.VideoCapture(4)

I realized from the previous posts that by iterating in a small range you probably will get the correct id in a few attempts

Stolzer