.TH FFT2D local "24 March 1993"
.SH NAME
.B fft2d 
\- to 2-d Fourier transform image files
.SH SYNOPSIS
.B fft2d
fname  [scale=] [real] [imag] [power] [inverse] [box=]
[verbose] [imag=] [outfile=]
.SH DESCRIPTION
.LP
This routine computes the 2-dimensional Fourier transform
of the file 'fname.fts'.  Unless over-ridden by the
outfile= option the output transform will be
written to the file 'fft.fts'. 
.LP
If the image rows and/or columns are not powers of two then
the image size if filled out to the next factor of two and
padded with zeroes.
.LP
If a 
.B box
is specified, then the operations are only carried out
over the box.
.LP
The transform is done in floating point.
As a default, the
modulus of the transform is written out.  The keywords 
.B real
and 
.B imag
and
.B power 
can be used to over-ride this selection, by writing the
real, imaginary and total power values of the transform instead
of the square root of the power.
If the
absolute value of the transform exceeds the range of an integer,
the data are scaled to 32768.  An optional 
.B scale
factor can
be entered to over-ride this selection.
.LP
The zero spatial frequency point is placed in the center of
the transformed image.
.LP         
Several messages are printed as the routine progresses if the
.B verbose
keyword is given.
.LP
The input file is assumed to be the real part.  
If you wish to do a complex transform the file containing the
imaginary part can be specified by using the  
.B imag=
option.
.SH EXAMPLE
.IP 
fft2d alphalyr real box=1 
.LP
Find the real part of the 2-D transform of the values inside
box 1 of the file 'alphalyr.fts'.
Place the output into the file 'fft.fts'.
.IP 
fft2d alphalyr image=wave scale=.1 power
.LP
Find the power of the complex 2-D transform which uses
the pixels in 'alphalyr.fts' as the real part, and
pixels in 'wave.fts' as the imaginary part, of 
a set of complex input values.
Scale the output by a factor of 0.1 before converting
to 16-bit signed integers for output to the FITS
file 'fft.fts'.
.SH BUGS
.LP
If you want complex output you must run the program twice.