i.ifft(1)

📦
version 8.4.2 · 8 versions
, in fedora 44

💖 i.ifft — bestie's guide to the Inverse Fast Fourier Transform 💖

okay so this is the page for i.ifft from the GRASS GIS User's Manual — GRASS 8.4.2 era, fr fr. it's a command-line module, and honestly? she's iconic. let's get into it 🦋

✨ NAME ✨

i.ifft — Inverse Fast Fourier Transform (IFFT) for image processing. the un-transformer!! 🎀

🔑 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 — let the output files just bulldoze any existing files that are already there, no questions asked 💅
  • --help — prints the usage summary so you're not out here guessing 🙈
  • --verbose — verbose module output, aka she will talk 🗣️
  • --quiet — quiet module output, aka she will NOT talk 🤫
  • --ui — force launch that GUI dialog, if you're feeling main character about it ✨

Parameters 🧚

  • real=name [required] — the name of the input raster map, specifically the image fft, real part 💜
  • imaginary=name [required] — the name of the input raster map, specifically the image fft, imaginary part 🌙
  • output=name [required] — the name for your output raster map, aka the whole point 🎁

💫 DESCRIPTION 💫

so i.ifft is an image processing program based on the algorithm given by Frigo et al. (1998), and what it does is genuinely so satisfying: it takes real and imaginary frequency space images — the ones produced by i.fft — and converts them back into a normal image. 🦋

like... you sent your image to frequency-space jail and now you're springing it back out. periodt. 🔥

📝 NOTES 📝

okay listen, this part matters, bestie:

  • the current mask is respected when reading the real and imaginary component files. so like, creating a mask is a primary step for selecting the portion of the frequency space data that gets included in the inverse transform. it's giving "no mask, no say." 💅
  • the module wxGUI vector digitizer can be used to create masks while you're 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 the circle/ring center. 🍩 no cap, donut filters are real.
  • and 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. she remembers. she's consistent. she's an icon. 👑
ngl the region thing is lowkey the most important vibe check here — same region as the forward transform, or your results are gonna be a mess 😭

📚 REFERENCES 📚

  1. 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. ⭐
  2. Richards, J.A (1986): Remote Sensing Digital Image Analysis, Springer-Verlag, 1986. 🌸
  3. 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

(go read i.fft too, they're a package deal, iykyk 💖)

👑 AUTHORS 👑

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

💻 SOURCE CODE 💻

Available at: i.ifft source code (history)

Accessed: Saturday Jan 17 05:41:45 2026

Main index | Imagery index | Topics index | Keywords index | Graphical index | Full index

and that's the whole page, bestie!! 💜 this was i.ifft from the GRASS GIS 8.4.2 Reference Manual, © 2003-2025 GRASS Development Team — page last touched Saturday Jan 17 05:41:45 2026, and the footer was giving GRASS 8.4.2 with i.ifft(1) down at the bottom, so now you know exactly where you are. slay, go transform something backwards 🌈✨💅

📦 where this page comes from