text: #!/usr/bin/env python
  
  '''
  This sample demonstrates Canny edge detection.
  
  Usage:
    edge.py [<video source>]
  
    Trackbars control edge thresholds.
  
  '''
  
  import cv2
  import video
  import sys
  
  
  if __name__ == '__main__':
      print __doc__
  
      try: fn = sys.argv[1]
      except: fn = 0
  
      def nothing(*arg):
          pass
  
      cv2.namedWindow('edge')
      cv2.createTrackbar('thrs1', 'edge', 2000, 5000, nothing)
      cv2.createTrackbar('thrs2', 'edge', 4000, 5000, nothing)
  
      cap = video.create_capture(fn)
      while True:
          flag, img = cap.read()
          gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
          thrs1 = cv2.getTrackbarPos('thrs1', 'edge')
          thrs2 = cv2.getTrackbarPos('thrs2', 'edge')
          edge = cv2.Canny(gray, thrs1, thrs2, apertureSize=5)
          vis = img.copy()
          vis /= 2
          vis[edge != 0] = (0, 255, 0)
          cv2.imshow('edge', vis)
          ch = cv2.waitKey(5)
          if ch == 27:
              break
      cv2.destroyAllWindows()
  