Tracking in the 1D case Iterating helps refining the velocity vector (x,1)1(x,1+1) Temporal derivative at 2nd iteration P Can keep the same estimate for spatial derivative v←1 Converges in about 5 iterations previous 1010 Tracking in the 1D case: x I ( x , t) I ( x , t + 1) p x I t I Temporal derivative at 2nd iteration Iterating helps refining the velocity vector Can keep the same estimate for spatial derivative x t previous I I v  v −   Converges in about 5 iterations