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

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

       output=name [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 component 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. Alternatively 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

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

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

           •   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)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual