Dense optical flow output

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Hi,

I'm using the optical flow algorithm implemented in the opencv motion analysis library (in particular that one that uses the Farneback approach). As known, the optical flow equation is the following:

fx * u + fy * v = - ft

where fx = df/dx, fy = df/dy, ft = df/dt and (u,y)^T = optical flow.

My question is about the "flow" values returned by calcOpticalFlowFarneback function. Is it the proper optical flow map (intended as velocity of the features expressed in pixels per seconds) or is it a displacement map of the image features?

Thanks in advance,

Antonio.