OpenCV: "[ WARN:0] terminating async callback" when attempting to take a picture

Question:

I am trying to take a picture from the defualt carmera with python, to do this I am using openCV (import cv2 as cv from python shell). However, when I attempt to disable the camera it closes but with the error [ WARN:0] terminating async callback.

This is code I am trying to run:

import cv2 as cv

camera_port = 0
camera = cv.VideoCapture(camera_port)
return_value, image = camera.read()
cv.imwrite("image.png", image)

camera.release() # Error is here

The code outputs the desired result, it takes and saves an image, but I do not understand why the error message occurs or how to remove it

Asked By: Elephant

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Source

Answers:

It’s probably showing a warning because you’re not releasing the handle to the webcam.

try adding this to the end of the code

camera.release()
cv2.destroyAllWindows()

I hope this helps!

Answered By: Aprajita Verma
  1. first:add cv.destroyAllWindows()
  2. second:the camera permission you have banned,and then check it.
Answered By: robot liu

I did this & I don’t see that warning there after.(only for Windows OS)

Open cmd and type:

setx OPENCV_VIDEOIO_PRIORITY_MSMF 0
Answered By: Little_being
camera = cv.VideoCapture(camera_port, cv.CAP_DSHOW)

cv.destroyAllWindows()
Answered By: Sumit kumar

It works for me as indicated Sumit Kumar


camera_port = 0
#camera = cv2.VideoCapture(camera_port)
camera = cv2.VideoCapture(camera_port,cv2.CAP_DSHOW)
# Check if the webcam is opened correctly
if not camera.isOpened():
    raise IOError("Cannot open webcam")

return_value, image = camera.read()
print("We take a picture of you, check the folder")
cv2.imwrite("image.png", image)

camera.release() # Error is here
cv2.destroyAllWindows()
Answered By: Joe Llerena

I had the same warning.

Just modify the line

camera = cv.VideoCapture(camera_port)

to

camera = cv.VideoCapture(camera_port, cv.CAP_DSHOW)
Answered By: Karl Djotchuang Tamo
camera = cv.VideoCapture(camera_port, cv.CAP_DSHOW) # Added cv.CAP_DSHOW
return_value, image = camera.read()
cv.imwrite("image.png", image)
camera.release()
cv.destroyAllWindows() # Handles the releasing of the camera accordingly
Answered By: Brady R

hey guys found the solution pip install opencv-contrib-python==3.4.7.28 try like this we have to specifically say the version try lesser version mine was 4.x so I did and no error popped up

Answered By: ARUN AK

This seems to be a bug in MSMF backend of opencv.

If you are using windows then you can change the backend to DirectShow backend.

So, change VideoCapture like this:

captureDevice = cv.VideoCapture(0, cv.CAP_DSHOW)
Answered By: Codemaker