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Capturing video using OpenCV

I am having an issue capturing the video feed, my camera light goes on and then off when i run this code. I tried using different values as well. And my camera seems to be working. but this code is not.
import cv2
cap = cv2.VideoCapture(0) # zero instead of one
while True:
ret, frame = cap.read()
if not ret: # exit loop if there was problem to get frame to display
break
cv2.imshow('frame', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()

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.

Cannot open a video using opencv 3.1 and python 3.6

I am trying to open a video using opencv 3.1 and python 3.6 using an Industrial camera "catchBest" . Its driver is installed and device is listed in device manager. But it is not opening using opencv.
Here's the code:
import cv2
video = cv2.VideoCapture(0)
while True:
cam = video.read()
cv2.imshow("video", cam)
cv2.waitKey(0)
video.release()
cv2.destroyAllWindows()
I tried index from 0 to 9 but its not working.

This should work:
import cv2
#you can run a loop from 0 to 100 to check which gives true, if you're unsure which number to use.
video = cv2.VideoCapture(0)
print(video.isOpened()) #this should return True if camera opens successfully.
while True:
#first returned value of video.read() is boolean and second is frame so we have to use second.
ret,cam = video.read()
cv2.imshow("video",cam)
#you have to break from infinite loop to release the camera usage, here I'm using escape key to break you can choose any.
if cv2.waitKey(1) & 0xFF == 27:
break
video.release()
cv2.destroyAllWindows()

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.

Grabbing Analog video into python using opencv

Well, it seems like my question had been asked many times before and unfortunately, no one replied. I hope someone will help.
I have an Easycap device that converts the analog images from my analog camera to digital signals through a USB port.
The device is identified to the system in the Device Manager under "Sound, Video and game controllers" category as "SMI Grabber Device".
I use a simple Python code to display the video from this device. I also have an embedded webcam in my laptop.
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# Display the resulting frame
cv2.imshow('frame',frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
if cv2.waitKey(1) & 0xFF == ord('s'):
cv2.imwrite('screenshot.jpg',frame)
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()
First, when I unplug the Easycap, CaptureVideo(0) returns the embedded webcam video stream. However, when I plug the Easycap, an error appears:
"Traceback (most recent call last):
File "C:\Users\DELL\Desktop\code\cam.py", line 10, in
cv2.imshow('frame',frame)
error: ......\src\opencv\modules\highgui\src\window.cpp:261: error: (-215) size.width>0 && size.height>0"
Notice that, any number except 0 makes the program display the webcam image. So if I tried cap = cv2.CaptureVideo(1), it will show the webcam, cap = cv2.CaptureVideo(20) is the same.
I also tried to enter "SMI Grabber Device" instead of 0 or 1 in the VideoCaptureconstructor function, but it didn't make any difference.
I'm using Windows 8, and I've installed the accompanying driver for Easycap. The software that comes with the driver (called ULead) works fine and display the CCTV camera video. I tried to display the images while I'm closing that program, and without, the result is the same.
I used before a C# program with Aforge library which had getCamList method or something which allowed me to choose the specific device I want to display from a comboBox. I can't find a similar function is opencv.
I'm using OpenCV 2.4.6. I didn't try the code on prior versions.
I really need to understand why this code doesn't work, knowing that I'm just a very beginner of opencv and image processing.
I hope someone can help.

I am using EasyCAP too.
You must check that ret is True.
I am use below code
while True:
ret, frame = vc.read()
if ret:
break
cv2.waitKey(10)
h, w = frame.shape[:2]
print h, w
while True:
ret, frame = vc.read()
if ret:
cv2.imshow(WID, frame)
if cv2.waitKey(1) == 27:
break

Let there be light!
On serious note, I struggled with the same problem and I hope this helps!
the original thread + answer