title: How to create Trackbars which do not call any function? OpenCV 3.1 with Python 2.7
body: <p>I'm trying to threshold an image. I have used the <code>cv2.createTrackbar</code> function as-<br>
   <code>cv2.createTrackbar('High H','image',0,179, None)</code>.<br>
  Now the last part is what I'm having trouble with. Further in my code, I use <code>highH = cv2.getTrackbarPos('High H','image')</code> to get my trackbar value and use it in the <code>cv2.inRange</code> function. So it becomes pretty obvious that I do not need to call a function as the last argument of the function. Now the problem is I can't seem to type in the function. I tried removing the last part, I got an error-  </p>
  
  <blockquote>
    <p>cv2.createTrackbar only works with 5 arguements. Only 4 given.  </p>
  </blockquote>
  
  <p>Hmm, okay  seems like I can't skip a part.<br>
  Next I tried callback and nothing. I got this error:-  </p>
  
  <blockquote>
    <p>When used nothing:- NameError: name 'nothing' is not defined<br>
    When used callback:- NameError: name 'callback' is not defined</p>
  </blockquote>
  
  <p>Okay after a while I tried using None. Got this error:-  </p>
  
  <blockquote>
    <p>TypeError: on_change must be callable</p>
  </blockquote>
  
  <p>So how do I use the <code>cv2.createTrackbar</code> function without calling a function?</p>
  
  <p>Thanks!</p>