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FF - Fourier Filter

(9/04/96)

PURPOSE

Applies filters to 2-D or 3-D Fourier transforms.

SEE ALSO

FF B [Fourier filter/bar ky direction]
FF BX [Fourier filter/bar kx direction]
FF PLOT [Design of filter]
FF S [Fourier filter, restore surface topograpy]
FP [Fourier interpolation]
FQ [Fourier quick]
FT [Fourier transformation]

USAGE

.OPERATION: FF

.INPUT FILE: FIN001
[Enter name of input file containing Fourier transform.]

.OUTPUT FILE: FOU001
[Enter name of output file containing filtered Fourier file.]

1: low-pass, 2: high-pass, 3: Gauss low-pass, 4: Gauss high-pass 5: Fermi low-pass, 6: Fermi high-pass, 7: Remez

.FILTER TYPE (1-7): 7
[Enter filter option code.

(1) Low-pass truncation. Filter is "top-hat" function that truncates Fourier transform at spatial frequency RAD.

(2) High-pass truncation. Filter is inverse "top-hat" function that passes Fourier transform beyond spatial frequency radius RAD.

(3) Gaussian low-pass. Filter is Gaussian function EXP(-f**2/(2.*RAD**2)), where F is the frequency.

(4) Gaussian high-pass. Filter is complement of Gaussian function: 1.0-EXP(-F**2/(2.*RAD**2)).

(5) Fermi low-pass. Filter is 1/(1+EXP[(F-RAD)/T]) which negotiates between "top-hat" and Gaussian characteristics, depending on the value of T (see below).

(6) Fermi high-pass. As low-pass, but T is replaced by -T.

(7) Multiplication by the Remez filter designed with the help of 'FF PLOT' command.

.FILTER RADIUS: 0.12
[Enter filter function radius in frequency units. They are of the range 0.0<=f<=0.5.]

For the Fermi filters [(5) and (6)], the temperature parameter T will be solicited:

.TEMPERATURE (0=CUTOFF): 0.3
[Roughly within this reciprocal distance (in terms of frequency units), the filter falls off.]

For the Remez filter (7), the filter file will be solicited:

.FILTER FILE: REM000
[This file can be created by 'FF PLOT', or it can be any Fourier file used as a filter.]

SUBROUTINES

FFILTS

CALLER

FOUR1

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