NAME
i.fft - Fast Fourier Transform (FFT) for image processing.
KEYWORDS
imagery, FFT
SYNOPSIS
i.fft
i.fft help
i.fft input_image=name real_image=name imaginary_image=name [--overwrite] [--verbose] [--quiet]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- input_image=name [required]
- Name of input raster map
- real_image=name [required]
- Name for output real part arrays stored as raster map
- imaginary_image=name [required]
- Name for output imaginary part arrays stored as raster map
DESCRIPTION
i.fft is an image processing program based on the FFT algorithm
given by Frigo et al. (1998), that processes a single input raster map layer
(input_image) and constructs the real and imaginary Fourier
components in frequency space.
NOTES
The real and imaginary components are stored into the
real_image and imaginary_image raster map
layers. In these raster map
layers the low frequency components are in the center and
the high frequency components are toward the edges. The
input_image need not be square. A
color table is assigned to the resultant map layer.
The current geographic region and mask settings are respected when
reading the input file. The presence of nulls or a mask will make the
resulting fast Fourier transform invalid.
EXAMPLE
North Carolina example:
g.region rast=lsat7_2002_70
i.fft input_image=lsat7_2002_70 real=lsat7_2002_70.real imaginary=lsat7_2002_70.imag
# set region to resulting FFT output map (due to new FFT coordinate space):
g.region rast=lsat7_2002_70.real -p
d.mon x0
d.rast lsat7_2002_70.real
d.rast lsat7_2002_70.imag
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.
- John A. Richards, 1986. Remote Sensing Digital Image Analysis, Springer-Verlag.
Personal communication, between progam author and Ali R. Vali,
Space Research Center, University of Texas, Austin, 1990.
i.cca
i.class
i.ifft
i.pca
AUTHOR
David Satnik, GIS Laboratory,
Central Washington University
Glynn Clements (FFTW support)
Last changed: $Date: 2011-11-08 13:24:20 -0800 (Tue, 08 Nov 2011) $
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