Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

## 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

*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

*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*.

- 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.

*
i.cca,
g.gui.iclass,
i.fft,
i.pca,
r.circle,
wxGUI vector digitizer
*
David Satnik, GIS Laboratory,
Central Washington University

Glynn Clements (FFTW support)

## SOURCE CODE

Available at:
i.ifft source code
(history)

Latest change: Monday Feb 27 13:45:25 2023 in commit: a82501dc85294207e8e58437c3ec7f1056465ed4

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GRASS Development Team,
GRASS GIS 8.3.3dev Reference Manual