Working toward efficient (real-time) implementations of optical flow methods, the authors have applied simple recursive filters to achieve temporal smoothing and differentiation of image intensity, and to compute 2d flow from component velocity constraints using spatiotemporal least-squares minimization. Accuracy in simulation is similar to that obtained in the study by Barren et al. (1994), while requiring much less storage, less computation, and shorter delays.>

The measurement of multiple velocities using phase-based methods is discussed. In particular, phase gradients (instantaneous frequency) from different bandpass channels (quadrature filter outputs) are used to estimate multiple image velocities in a single neighborhood. The approach is similar to that of M. Shizawa and K. Mase (1990) in which nth-order differential operators are required to compute n simultaneous velocity estimates. However, to use instantaneous frequency, the output of each channel must be differentiated only once.>