i.ifft(1grass)

✨ i.ifft — the inverse FFT glow-up ✨

okay bestie, welcome to i.ifft, straight outta the GRASS User's Manual 💖 this is the manual page for i.ifft(1grass) and she is iconic. sit down, grab a strawberry, we're doing math.

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🌸 NAME 🌸

i.ifft — Inverse Fast Fourier Transform (IFFT) for image processing. it takes your frequency-space vibes and turns them back into a real actual picture. periodt.

🎀 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 — bestie she said move, let the output files overwrite the existing ones. yes literally bulldoze them.
• --help — prints the usage summary so you stop guessing 🙈
• --verbose — verbose module output, she's telling you everything
• --quiet — quiet module output, she's giving mysterious & silent ✨
• --ui — force launching the GUI dialog, for when you want the pretty buttons

💜 Parameters:

• real=name [required] — name of input raster map (the real part of the image fft)
• imaginary=name [required] — name of input raster map (the imaginary part of the image fft)
• output=name [required] — name for the output raster map 🌈

👑 DESCRIPTION 👑

so i.ifft is an image processing program, no cap, and she's based on the algorithm given by Frigo et al. (1998). what she does is take real and imaginary frequency space images — the ones produced by i.fft — and convert them back into a normal image. it's the un-transformation. the reversal. the "okay we're done in the frequency dimension, come back to earth" moment 🫶

🔥 NOTES 🔥

the way that this matters: the current mask is respected when reading the real and imaginary component files 🔥 so making a mask? that's literally the primary step for selecting the portion of the frequency space data that's gonna be included in the inverse transform. mask = the main character here, fr fr.

the module wxGUI vector digitizer can be used to create masks while you're viewing the real or imaginary component image. casual.

alternatively — and this is the slay part — r.circle can be used to generate high-, low- and donut filters by specifying the DC point as the circle/ring center 🍩

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 keeps receipts. 💅

⭐ 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

🌈 AUTHORS 🌈

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

🧚 SOURCE CODE 🧚

Available at: i.ifft source code (history)

Latest change: Friday Jan 02 21:25:59 2026 in commit: 83362df5af36c1e7d95fad93dff0a57b4dfde476

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

© 2003-2026 GRASS Development Team, GRASS 8.5.0 Reference Manual

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okay that's the whole thing, you ate that 🫶 now go invert some frequencies and be free

so this page is i.ifft(1grass) from the GRASS User's Manual, and it's GRASS 8.5.0, latest change Friday Jan 02 21:25:59 2026 — love that for us, mwah 💖✨🎀