% @(#)fft_imag.hlq	19.1 (ESO-IPG) 02/25/03 14:03:20 
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1990 European Southern Observatory
%.IDENT      fft_imag.hlq
%.AUTHOR     KB, IPG/ESO
%.KEYWORDS   MIDAS, help files, FFT/IMAGE
%.PURPOSE    On-line help file for the command: FFT/IMAGE
%.VERSION    1.0  03-APR-1990 : Creation, KB
%.VERSION    1.1  26-OCT-1992 : Upgrade, KB
%----------------------------------------------------------------
\se
SECTION./IMAG
\es\co
FFT/IMAGE						26-OCT-1992  KB
\oc\su
FFT/IMAGE inr ini outr outi
	make discrete Fourier transform
\us\pu
Purpose:      
           Compute the discrete Fourier transform of real or complex frame.
\up\sub
Subject:      
           Transformation, filter.
\bus\sy
Syntax:       
           FFT/IMAGE inr ini outr outi
\ys\pa
           inr = frame containing the real part of input frame
\ap\pa
           ini = frame containing the imaginary part of input frame;
\\
                if input frame is real, omit parameter `ini' or set it to `?'
                if you enter values for any of the following parameters.
\ap\pa
           outr = frame for real part of result transform,
                defaulted to `fftr.bdf'
\ap\pa
           outi = frame for imaginary part of result transform,
                defaulted to `ffti.bdf'
\ap\sa
See also:
           FFT/INVERSE, FFT/POWER, FFT/FREQUENCY, CREATE/FILTER
\as\no
Note:         
           All internal calculations are done in double precision and
           only the final result frames are truncated to single precision.
\\
           To calculate the inverse Fourier transformation use FFT/INVERSE,
           not FFT/FINVERSE which only works for frames obtained with the
           FFT/FREQUENCY command!
\\
           If the number of pixels in an axis of the input frame is not a power
           of 2, the input frame is expanded to the next higher power of 2.
           The result frames will have the original no. of pixels but the
           result frames with expanded size are also kept with names
           `exp_fftr.bdf' and `exp_ffti.bdf'. These frames should be used later
           when calculating the inverse Fourier transform via FFT/INVERSE!
\\
           The FFT command does NOT work for 3-dim frames.
\on\exs
Examples:
\ex
           FFT/IMA rr ri
             Do FFT for image where real part is contained in frame `rr.bdf'
             and imaginary part in frame `ri.bdf'. The real and imaginary parts
             of the FFT are stored in `fftr.bdf' and `ffti.bdf'.
\xe\ex
           FFT/IMA lola ? zr zi
             Do FFT for real frame `lola.bdf' (no imaginary part) and store
             results in `zr.bdf' and `zi.bdf'.
\xe\sxe
