SN RB - SNR Butterworth

PURPOSE

Fit a Butterworth filter to the FSC curve.   Example.

SEE ALSO

SN RF	[SNR Filter]
RF 3	[Phase Residual & Fourier shell correlation, 3D ||]
TF SNR	[Transfer Function - CTF correction, using frequency dependent SNR]

USAGE

.OPERATION: SN RB [pass],[stop]

[Optional output register variables: [pass] & [stop] will receive pass and stop frequencies of a Butterworth filter.]

.FSC INPUT DOC FILE: dres001
[Enter name of document file containing FSC computed using 'RF 3'.]

.LOW PASS OR HIGH PASS (L/H): L
[Enter the type of filter.]

NOTES

1. The purpose of this command is to estimate an FSC-based smooth curve that approximates SSNR distribution in the data. The SSNR curve can then be used in "TF WCTF"

2. The Butterworth filter is above the FSC curve.

3. See 'TF SNR'.

4. Implemented by: L. Joyeux

SUBROUTINES

SNRB

CALLER

UTIL4