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


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


imagery, transformation, Fast Fourier Transform


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


Allow output files to overwrite existing files

Print usage summary

Verbose module output

Quiet module output

Force launching GUI dialog


Name of input raster map (image fft, real part)

Name of input raster map (image fft, imaginary part

Name for output raster map


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.


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 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.


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


  • M. Frigo and S. G. Johnson (1998): "FFTW: An Adaptive Software Architecture for the FFT". See 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.


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


Available at: i.ifft source code (history)

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© 2003-2021 GRASS Development Team, GRASS GIS 7.8.6 Reference Manual

GRASS 7.8.6