Differential Techniques Second-order differential In (x, t)I(x, On./Iu(x, l(x,)n(x,) xt 0 Stronger restriction than first-order derivatives on permissible motion field VI(x.,1)v+l1(x,)=0 Can be combined with 1st order in isolation or together(over determined system) Velocity estimation from 2nd-order methods are often assumed be to sparser and less accurate than estimation from 1st-order methodsDifferential Techniques • Second-order differential • Stronger restriction than first-order derivatives on permissible motion field • Can be combined with 1st order in isolation or together (over￾determined system) • Velocity estimation from 2nd -order methods are often assumed be to sparser and less accurate than estimation from 1st -order methods 1 2 ( , ) ( , ) ( , ) 0 ( , ) ( , ) ( , ) 0 xx yx tx xy yy tx I t I t v I t I t I t v I t           + =            x x x x x x ( , ) ( , ) 0 t   + = I t I t x v x