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i.ifft(1)		    GRASS GIS User's Manual		     i.ifft(1)

NAME
       i.ifft  - Inverse Fast Fourier Transform	(IFFT) for image processing.

KEYWORDS
       imagery,	transformation,	Fast Fourier Transform

SYNOPSIS
       i.ifft
       i.ifft --help
       i.ifft  real=name  imaginary=name  output=name  [--overwrite]  [--help]
       [--verbose]  [--quiet]  [--ui]

   Flags:
       --overwrite
	   Allow output	files to overwrite existing files

       --help
	   Print usage summary

       --verbose
	   Verbose module output

       --quiet
	   Quiet module	output

       --ui
	   Force launching GUI dialog

   Parameters:
       real=nameA [required]
	   Name	of input raster	map (image fft,	real part)

       imaginary=nameA [required]
	   Name	of input raster	map (image fft,	imaginary part

       output=nameA [required]
	   Name	for output raster map

DESCRIPTION
       i.ifft is an image processing program based on the algorithm  given  by
       Frigo  et  al. (1998), that converts real and imaginary frequency space
       images (produced	by i.fft) into a normal	image.

NOTES
       The current mask	is respected when reading the real and imaginary  com-
       ponent  files;	thus,  creating	a mask is a primary step for selecting
       the portion of the frequency space data to be included in  the  inverse
       transform.   The	 module	 wxGUI	vector digitizer can be	used to	create
       masks while viewing the real or	imaginary  component  image.  Alterna-
       tively  r.circle	 can be	used to	generate high-,	low- and donut filters
       specifying the DC point as circle/ring center. When i.ifft is executed,
       it  (automatically)  uses the same GRASS	region definition setting that
       was used	during the original transformation done	with i.fft.

SEE ALSO
	i.cca, g.gui.iclass, i.fft, i.pca, r.circle, wxGUI vector digitizer

REFERENCES
	   o   M. Frigo	and S. G. Johnson (1998): "FFTW: An Adaptive  Software
	       Architecture  for  the FFT". See	www.fftw.org: FFTW is a	C sub-
	       routine library for computing the  Discrete  Fourier  Transform
	       (DFT) in	one or more dimensions,	of both	real and complex data,
	       and of arbitrary	input size.

	   o   Richards, J.A (1986): Remote Sensing  Digital  Image  Analysis,
	       Springer-Verlag,	1986.

	   o   Personal	communication, between program author and Ali R. Vali,
	       Space Research Center, University of Texas, Austin, 1990.

AUTHORS
       David Satnik, GIS Laboratory, Central Washington	University
       Glynn Clements (FFTW support)

SOURCE CODE
       Available at: i.ifft source code	(history)

       Main index | Imagery index | Topics index | Keywords index |  Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.4 Reference	Manual

GRASS 7.8.4							     i.ifft(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | NOTES | SEE ALSO | REFERENCES | AUTHORS | SOURCE CODE

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