title: How to fix opencv import for TVL1 opticalflow algorithm
body: <p>I'm asking you a very simple question. I want to use the TVL1 function for computing opticalflow with openCV (and python). But here is what I get :</p>
  
  <pre><code>AttributeError: 'module' object has no attribute 'DualTVL1OpticalFlow_create'
  
  Traceback (most recent call last):
  
  File "opticalFlowModel.py", line 50, in computeOpticalFlow
  optical_flow = cv2.DualTVL1OpticalFlow_create()
  
  AttributeError: 'module' object has no attribute 'DualTVL1OpticalFlow_create'
  </code></pre>
  
  <p>The problem is that in this topic <a href="https://stackoverflow.com/questions/37871443/how-to-compute-optical-flow-using-tvl1-opencv-function">How to compute optical flow using tvl1 opencv function</a> , they seems to use the exact same code. I also try this code : <a href="https://stackoverflow.com/questions/53209087/speed-up-optical-flow-algorithm-if-applicable-python-opencv">Speed Up Optical Flow algorithm (If applicable) Python OpenCV</a> and have the same result.</p>
  
  <p>Here are all my import :</p>
  
  <pre><code>import cv2
  import numpy as np
  from PyQt4.QtGui import *
  from PyQt4.QtCore import *
  from PyQt4 import QtCore, QtGui
  </code></pre>
  
  <p>I'm using OpenCV 4.0.1</p>