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I have this problem with opencv python on Macbook

My problem is when I try to run this code on my Mac, the camera turns on the green light but it doesn't open at all. I have no idea why this is happing. I tried a lot of things but nothing worked for me, I am just thinking the new update from Apple messed up some stuff, because it used to work before.
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# Our operations on the frame come here
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2BGRA)
# 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()

In mac you have to use the Mac Terminal for the cv2 library since currently no other terminal to my knowledge asks for the camera permission.

Using OpenCV for python to capture webcam get white screen grab

I'm using python 2.7 on DragonBoard 410c with Debian OS to capture webcam Logitech C920 by opencv but get a white sceen result.
Here is my whole code.
import cv2
cap = cv2.VideoCapture(0)
cap.set(3,1280)
cap.set(4,720)
while(cap.isOpened()):
ret, frame = cap.read()
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2BGRA)
cv2.imshow('frame', gray)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
It worked well without the code "cap.set(3,1280)" and "cap.set(4,720)".
I can get the frame with 640x480.
but if I added the code to change the resolution, the window would change but the frame is white.
https://imgur.com/flsKfTp
By the way, if I set the resolution to 800x600, the frame will flash between white sceen and camera view.
How can I solve this problem?

Trying to read an online video using OpenCV in python, Not seeing the output but the code is not throwing any error

Not sure what is the problem. Code is running fine and not showing any error. But Not seeing any output.
import numpy as np
import cv2
cap = cv2.VideoCapture("https://youtu.be/_3elg-_1m_c")
while(cap.isOpened()):
ret, frame = cap.read()
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.imshow('frame',gray)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
If, I am using video saved in my laptop, I can see the output, but for online vidoes, I am not.

How do I create an executable in python using Opencv on OsX ?

Here is my code :
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# Our operations on the frame come here
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
# Display the resulting frame
cv2.imshow('frame',gray)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()
I used py2app to make an executable,
and when I run the code, an error window opens
"name of file error"
How do I fix this code in order to make a working executable ?

Webcam + Open CV Python | Black screen

I am using the code below, but I get a black image. Could you please help me rectify the error?
import cv2
import numpy as np
c = cv2.VideoCapture(0)
while(1):
_,f = c.read()
cv2.imshow('e2',f)
if cv2.waitKey(5)==27:
break
cv2.destroyAllWindows()

Update: See github.com/opencv/opencv/pull/11880 and linked conversations, only few backends support -1 as index.
Although this is an old post, this answer can help people who are still facing the same problem. If you have a single webcam but it renders all black, use cv2.VideoCapture(-1). This will get you the working camera.

Just change cv2.waitKey(0) to cv2.waitKey(30) and this issue will be resolved.

I've faced with same problem. Updating neither opencv nor webcam driver works. I am using kaspersky as antivirus. When I disable the kaspersky, then black output problem solved.
BTW, I can see the running .py file in kaspersky console > reports > host intrusion prevention. It reports application privilege control rule triggered - application: myfile.py, result: blocked: access to video capturing devices

Try this:
import cv2
import numpy as np
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()

This worked for me:
I did a pip install imutils. Imutils is a library with series of convenience functions to make basic image processing functions such as translation, rotation, resizing, skeletonization, displaying Matplotlib images, sorting contours, detecting edges, and much more easier with OpenCV and both Python 2.7 and Python 3.
import cv2
import imutils
cap = cv2.VideoCapture(0) # video capture source camera (Here webcam of laptop)
ret, frame = cap.read() # return a single frame in variable `frame`
while (True):
# gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
(grabbed, frame) = cap.read()
frame = imutils.resize(frame, width=400)
cv2.imshow('img1', frame) # display the captured image
if cv2.waitKey(1) & 0xFF == ord('q'): # save on pressing 'y'
cv2.imwrite('capture.png', frame)
cv2.destroyAllWindows()
break
cap.release()

Try put -0 on the index and pause any antivirus running
import cv2
import numpy as np
cap = cv2.VideoCapture(-0)
cap.set(3,640)
cap.set(3,480)
while(True):
success, img = cap.read()
cv2.imshow('frame',img)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()

I faced the same issue after many calls with:
cap = cv2.VideoCapture(0)
and it solved when I changed the index to 1 :
cap = cv2.VideoCapture(1)

In my case just disabling Kaspersy has solved the problem.