Posted by xoc bob on November 06, 2002 at 13:30:07:
In Reply to: Question about high pass filter posted by Lin HE on October 31, 2002 at 00:03:43:
3dTsmooth is a lowpass filter, not a highpass filter.
3dDetrend could do a highpass filter (by giving it enough basis functions to span the lowpass function space), but that's the hard way.
3dFourier is what you want. If you want to reject everything below a period of 144 seconds, then the cutoff frequency is 1/144=0.00694444, and a command line to use would be something like
3dFourier -prefix fred_hipass -highpass 0.00694444 fred+orig
bob cox