Provided by: grass-doc_7.8.2-1build3_all

**NAME**

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

**KEYWORDS**

imagery, transformation, Fast Fourier Transform

**SYNOPSIS**

i.iffti.ifft--helpi.ifftreal=nameimaginary=nameoutput=name[--overwrite] [--help] [--verbose] [--quiet] [--ui]Flags:--overwriteAllow output files to overwrite existing files--helpPrint usage summary--verboseVerbose module output--quietQuiet module output--uiForce launching GUI dialogParameters:real=name[required]Name of input raster map (image fft, real part)imaginary=name[required]Name of input raster map (image fft, imaginary partoutput=name[required]Name for output raster map

**DESCRIPTION**

i.ifftis an image processing program based on the algorithm given by Frigo et al. (1998), that converts real and imaginary frequency space images (produced byi.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 modulewxGUIvectordigitizercan be used to create masks while viewing the real or imaginary component image. Alternativelyr.circlecan be used to generate high-, low- and donut filters specifying the DC point as circle/ring center. Wheni.ifftis executed, it (automatically) uses the same GRASS region definition setting that was used during the original transformation done withi.fft.

**SEE** **ALSO**

i.cca,g.gui.iclass,i.fft,i.pca,r.circle,wxGUIvectordigitizer

**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):RemoteSensingDigitalImageAnalysis, Springer-Verlag, 1986. · Personal communication, between program author and Ali R. Vali, Space Research Center, University of Texas, Austin, 1990.

**AUTHORS**

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

**SOURCE** **CODE**

Available at: i.ifft source code (history) Main index | Imagery index | Topics index | Keywords index | Graphical index | Full index © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual