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**NAME**

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

**KEYWORDS**

imagery, FFT

**SYNOPSIS**

i.iffti.iffthelpi.ifftreal_image=nameimaginary_image=nameoutput_image=name[--overwrite] [--verbose] [--quiet]Flags:--overwriteAllow output files to overwrite existing files--verboseVerbose module output--quietQuiet module outputParameters:real_image=nameName of input raster map (image fft, real part)imaginary_image=nameName of input raster map (image fft, imaginary partoutput_image=nameName 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 GRASS programr.digitcan 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. The real and imaginary components are read from arrays of doubles in thecell_miscdirectory (produced by the forward transform program,i.fft), and the reconstructed image will preserve the cell value scaling of the original image processed byi.fft. No color table is assigned to the output map; one should be created before viewing theoutput_image.

**SEE** **ALSO**

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.RemoteSensingDigitalImageAnalysis, by John A. Richards, Springer-Verlag, 1986. Personal communication, between program author and Ali R. Vali, Space Research Center, University of Texas, Austin, 1990.i.cca,i.class,i.fft,i.pca,r.circle

**AUTHOR**

David Satnik, GIS Laboratory, Central Washington University Glynn Clements (FFTW support)Lastchanged:$Date:2011-11-0801:42:51-0800(Tue,08Nov2011)$Full index © 2003-2013 GRASS Development Team