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.

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.

SEE ALSO

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

AUTHORS

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

SOURCE CODE

       Available at: i.ifft source code (history)

       Accessed: Thursday Aug 01 11:31:46 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.4.0 Reference Manual