Signal-to-Noise ratio

The output from MatPIV can, apart from the velocities, also include the Signal-To-Noise ratio and the peak-height for use in validation of the vector field. The file snrfilt.m is used to validate the vector field with regards to the Signal-To-Noise ratio output from matpiv. The calling sequence looks like:

[su,sv]=snrfilt(x,y,u,v,snr,threshold,actions);

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 $1.3$ 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.