Calculating optical flow with opencv

Question

I am using the function:

cvCalcOpticalFlowBM

To calculate the optical flow. The code is running, but the velocity matrices are zero (both x and y), although the input video clearly changes. Does anyone have an idea why would the velocity matrices be zero (black)?

Answer 1

This tutorial shows how to use optical flow in opencv from scratch. It explains how to draw velocity vectors etc.

http://robots.stanford.edu/cs223b05/notes/CS%20223-B%20T1%20stavens_opencv_optical_flow.pdf