Usage: 3dnoise [-blast] [-snr fac] [-nl x ] datasets ...
Estimates noise level in 3D datasets, and optionally
set voxels below the noise threshold to zero.
This only works on datasets that are stored as shorts,
and whose elements are all nonnegative.
  -blast   = Set values at or below the cutoff to zero.
               In 3D+time datasets, a spatial location
               is set to zero only if a majority of time
               points fall below the cutoff; in that case
               all the values at that location are zeroed.
  -snr fac = Set cutoff to 'fac' times the estimated
               noise level.  Default fac = 2.5.  What to
               use for this depends strongly on your MRI
               system -- I often use 5, but our true SNR
               is about 100 for EPI.
  -nl x    = Set the noise level to 'x', skipping the
               estimation procedure.  Also sets fac=1.0.
               You can use program 3dClipLevel to get an
               estimate of a value for 'x'.
Author -- RW Cox

++ Compile date = Aug 21 2020 {AFNI_20.2.14:linux_ubuntu_16_64}