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 Oct 30 22:18:50 2025

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       © 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual

GRASS 8.4.1                                                                                       i.ifft(1grass)