OpenCV wont' capture from MacBook Pro iSight

Question

Since a couple of days I can't open my iSight camera from inside an opencv application any more. cap = cv2.VideoCapture(0) returns, and cap.isOpened() returns true. However, cap.grab() just returns false. Any ideas?

Example Code:

import cv2

cv2.namedWindow("preview")
vc = cv2.VideoCapture(0)
rval = True

while rval:
    rval, frame = vc.read()
    cv2.imshow("preview", frame)

    key = cv2.waitKey(20)
    if key == 27: # exit on ESC
        break

• Mac OS 10.8.5
• Python 2.7.5 (but also not working from inside a C++ app)
• OpenCV 2.4.6.1

Sanderling

Did you figure this out? I'm asking again here: #19187576 – Necrose

Answer 1

This is how I got the camera working for your code (on OSX 10.6):

import cv2

cv2.namedWindow("preview")
vc = cv2.VideoCapture(0)

rval, frame = vc.read()

while True:

  if frame is not None:   
     cv2.imshow("preview", frame)
  rval, frame = vc.read()

  if cv2.waitKey(1) & 0xFF == ord('q'):
     break

Washer

Thanks. Seems to work again after a complete reinstall. Also, maybe it took longer to set up the input channel. A frame actually only comes in on the second or third call to read(). Did not have this problem earlier – Sanderling

How did you install OpenCV on mac? – Mutable

Answer 2

I had a segmentation fault after I grab an image. It turned out that I used cv2.destroyAllWindows() before cap.release(). Below I show working code.

cap = cv2.VideoCapture(0)

while(True):
    ret, frame = cap.read()
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

#do some ops

cap.release()
cv2.imshow("output", output)
cv2.waitKey(0)
cv2.destroyAllWindows()

This code works on El Captain.

Tebet

Please edit your answer to explain what your code does and how it answers the question? – Constitutionality

@alex-attinger has a problem with grabbing image. I showed my code which grab a picture and works on macOS. – Tebet

I understand that your code might solve the problem, but it's a lot more useful if you explain what was wrong with the original and how your code actually solves the question. Especially given this question is from 2013 – Constitutionality