title: cannot get frame from openni device in python-opencv
body: <p>I am using raspberry pi to get frames from ASUS Xtion openni device.</p>
  
  <p>Python-opencv, OpenNI, and OpenCV are installed on raspberry pi correctly.</p>
  
  <p>I am using the following code:</p>
  
  <pre><code>import cv2
  import cv2.cv as cv
  
  capture = cv2.VideoCapture(cv.CV_CAP_OPENNI)
  capture.set(cv.CV_CAP_OPENNI_IMAGE_GENERATOR_OUTPUT_MODE. cv.CV_CAP_OPENNI_VGA_30HZ)
  
  okay, color_image = capture.retrieve(0, cv.CV_CAP_OPENNI_BGR_IMAGE)
  </code></pre>
  
  <p>This code was working without any problems before. But now, I always get "okay" value as "false". How can I fix this problem?</p>
  
  <p>Thanks,</p>