Here the final input actions can be ommited (typically in batch processing), or specified as 'loop'. The 'loop' option will allow the user to change the threshold value interactively and view the effect the changes has on the vector field. All the ``invalid'' velocity vectors (with a SnR lower than the threshold) are replaced with NaN (Not A Number). Keane and Adrian Keane and Adrian (1992) suggest that a threshold value of about is appropriate, so that normally something like
>> [su,sv]=snrfilt(x,y,u,v,snr,1.3);will give good results, but this will obviously depend on the quality of your images.