title: How to set parameters for DeepFlow optical flow algorithm
body: <p>The <a href="http://docs.opencv.org/3.1.0/d2/d84/group__optflow.html#ga5e735547610172695cb0b39495af9d6d" rel="nofollow">documentation of <code>cv::optflow::createOptFlow_DeepFlow</code></a> states:</p>
  
  <pre><code>Parameters - class fields - that may be modified after creating a class instance
  </code></pre>
  
  <p>How can one modify these parameters? All one gets is a <code>Ptr&lt;DenseOpticalFlow&gt;</code> and <a href="https://github.com/Itseez/opencv_contrib/blob/4ed940cc9f0ab586804fe0a90a5d9898402be5cf/modules/optflow/src/deepflow.cpp#L51" rel="nofollow"><code>cv::optflow::OpticalFlowDeepFlow</code></a> is not in the public interface, so one can not even <code>dynamic_cast</code> to it. </p>