How do I visualize optical flow using colors

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C#

Emgu-CV

OpenCV

Im trying to set different color based on the object movement using Optical Flow on EmguCv.

https://www.youtube.com/watch?v=ssINeWRb58M[^]

Please refer the above video.

I was able to get the flow of two consecutive frames using

OpticalFlow.Farneback(prev, frame1,velx, vely, 0.5, 1, 1, 2, 5, 1.1,
                  Emgu.CV.CvEnum.OPTICALFLOW_FARNEBACK_FLAG.USE_INITIAL_FLOW);

Still I cannot Understand how to use the velx and vely to visualize the flow like in the video.Can someone help me with this.I really appreciate it.

thanks