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

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

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.