OpenCv error can't open camera through video capture

Question

I was using my cam through opencv and suddenly after restarting I ran my code it shows below error:

[ WARN:0] global /io/opencv/modules/videoio/src/cap_v4l.cpp (802) open VIDEOIO ERROR: V4L: can't open camera by index 0
Traceback (most recent call last):
  File "test.py", line 20, in <module>
    retval, buffer_img = cv2.imencode('.jpg', frame)
cv2.error: OpenCV(4.1.2) /io/opencv/modules/imgcodecs/src/loadsave.cpp:877: error: (-215:Assertion failed) !image.empty() in function 'imencode'

cap = cv2.VideoCapture(0)  # here it throws an error


import json
while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    retval, buffer_img = cv2.imencode('.jpg', frame)

    resdata = base64.b64encode(buffer_img)

    resdata = "data:image/png;base64,"+ str(resdata.decode("utf-8"))
    PARAMS = {'image': resdata}

    # Our operations on the frame come here
    #gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

I also tried with cap = cv2.VideoCapture(1) but then it shows can't find camera

How can I fix this issue?

Answer 1

I got the same error. Try changing 0 to -1

cap = cv2.VideoCapture(-1)

This solved the issue.

Answer 2

I got the same problem when I created more than one instance of the cv2.VideoCapture(0). So check if your code contains multiple initializations or sections which call cv2.VideoCapture(0) more than once. I was facing this problem while running the flask server in debug mode because it called cv2.VideoCapture(0) twice.

import cv2
cap = cv2.VideoCapture(0)
cap2 = cv2.VideoCapture(0)
while True:

    ret, frame = cap.read()
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

Error:

python3 debugCamera.py 
[ WARN:0] global /io/opencv/modules/videoio/src/cap_v4l.cpp (887) open VIDEOIO(V4L2:/dev/video0): can't open camera by index

Answer 3

Most likely a permission issue on /dev/video0 .

Check if you are part of "video" group.
id -a

if you don't see video in your group list add sudo usermod -a -G video

for Ubuntu users:(20.04)
sudo usermod -a -G video $LOGNAME

Logout and log back in and try it.

Answer 4

I've encountered the same issue and attempted several methods like cv2.VideoCapture(-1) or cv2.VideoCapture(1) but without much success.

I succeeded after reading this article and disabling debug-mode

Answer 5

I will not go to that part What you are trying to do, here is just a block of code that can open your camera every time you run it,

python: 3.7.3

OpenCV: 4.1.0

import cv2
cap = cv2.VideoCapture(0)
while True:

    ret, frame = cap.read()
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

Answer 6

In my case, I just reconnected cam to the usb port, and then it was solved! I think this error is caused by closing the window in the wrong way. Please check if there is any exception on the terminal right after closing the window.

Answer 7

I found a solution in https://github.com/opencv/opencv/issues/19527 where the video capture is inside the function instead of outside. That worked for me (ubuntu)

def frame_generation():

camera = cv2.VideoCapture(0) #resolved, correct position

while(True):

Answer 8

我遇到了同样的问题，只需将 0 更改为 1，然后更改为 -1，然后再更改为 0。不知道为什么这对我有用。

Answer 9

This issue is due to the interruption. Try to end the execution with the key 'q' for example, don't close the window suddenly.

I solved the same issue by opening terminal again and execute the same script again.

Answer 10

I also had the same problem. Just changed it to 1 and it was perfectly working. I guess it's related to the number of camera devices you have used.

For example, I guess I have Iruin external camera as my first option which I didn't connect this time.

Here is the error and corrected code.

global /tmp/pip-req-build-f51eratu/opencv/modules/videoio/src/cap_v4l.cpp (890) open VIDEOIO(V4L2:/dev/video0): can't open camera by index

Code to change:

vid = cv2.VideoCapture(1)

Answer 11

对于 Linux，确保 OpenCV 是使用 WITH_V4L 构建的（带有用于 linux 的视频）。

Answer 12

I've also had this problem on Ubuntu

I've solved this by these comands

sudo adduser username video sudo usermod -a -G video username

username - it is the name of your device

than write

id -a

and copy index from ()

for me it is 1000

so than just write:

camera = cv2.VideoCapture(1000)

Answer 13

The OP appears to be operating on a Raspberry PI. Raspberry is moving to a new system to manage cameras, so when the user upgrades the OS via sudo apt-get upgrade the camera system gets the new library and the legacy camera system is disabled. To enable the legacy camera system again, try

sudo raspi-config

Then select

3 Interface Options    Configure connections to peripherals

then select

I1 Legacy Camera Enable/disable legacy camera support

and follow the directions to enable and then reboot.

Of course, this patch will only work for so long, as the legacy system has been deprecated.

Answer 14

Tried every anwser but only changing camera id from -1 to 1 and then back to 0 worked.

Answer 15

I have do everytime after restart or unplug usb camera and replug

chmod 777 /dev/video0

Answer 16

video = cv2.VideoCapture(0,cv2.CAP_DSHOW)

This worked for me.

Answer 17

Don't know if this is still an issue. In my case, I was getting the same error until I unplugged and plugged the usb camera. Even if I reboot, the error happened.

It's similar to someone said: my camera was already been captured. The problem is that it was not used by my script, so it was hard to identify.

A few days before the issue, I installed the motion library, but just to test something and I didn't use it anymore. The motion starts at boot, so the camera was being captured by the service. That's why only the unplug-plug worked.

I uninstalled the library, and the error was gone.