.TH i.ifft 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBi.ifft\fR\fR  \- Inverse Fast Fourier Transform (IFFT) for image processing.
.SH KEYWORDS
imagery, transformation, Fast Fourier Transform
.SH SYNOPSIS
\fBi.ifft\fR
.br
\fBi.ifft \-\-help\fR
.br
\fBi.ifft\fR \fBreal\fR=\fIname\fR \fBimaginary\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBreal\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input raster map (image fft, real part)
.IP "\fBimaginary\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input raster map (image fft, imaginary part
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output raster map
.SH DESCRIPTION
\fIi.ifft\fR 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
\fIi.fft\fR) into a normal image.
.SH 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 \fIwxGUI vector digitizer\fR
can be used to create masks while viewing the real
or imaginary component image. Alternatively \fIr.circle\fR can be
used to generate high\-, low\- and donut filters specifying the DC point
as circle/ring center. When \fIi.ifft\fR is executed, it
(automatically) uses the same GRASS region definition setting that was
used during the original transformation done with
\fIi.fft\fR.
.SH SEE ALSO
\fI
i.cca,
g.gui.iclass,
i.fft,
i.pca,
r.circle,
wxGUI vector digitizer
\fR
.SH REFERENCES
.RS 4n
.IP \(bu 4n
M. Frigo and S. G. Johnson (1998): \(dqFFTW: An Adaptive Software
Architecture for the FFT\(dq. 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.
.IP \(bu 4n
Richards, J.A (1986): \fBRemote Sensing Digital Image
Analysis\fR, Springer\-Verlag, 1986.
.IP \(bu 4n
Personal communication, between program author and Ali R. Vali,
Space Research Center, University of Texas, Austin, 1990.
.RE
.SH AUTHORS
David Satnik, GIS Laboratory,
Central Washington University
.br
Glynn Clements (FFTW support)
.SH SOURCE CODE
.PP
Available at: i.ifft source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual