---
name: "i.ifft"
section: "1grass"
platform: "linux"
package: "grass-doc"
version: "8.4.1-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/i.ifft"
---

# i.ifft(1grass)

Inverse Fast Fourier Transform (IFFT) for image processing.

## 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: Monday Feb 24 17:51:40 2025

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