i.fft.1grass - Man Page

Fast Fourier Transform (FFT) for image processing.

Keywords

imagery, transformation, Fast Fourier Transform

Synopsis

i.fft
i.fft --help
i.fft input=name real=name imaginary=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

Flags

--overwrite

Allow output files to overwrite existing files

--help

Print usage summary

--verbose

Verbose module output

--quiet

Quiet module output

--ui

Force launching GUI dialog

Parameters

input=name [required]

Name of input raster map

real=name [required]

Name for output real part arrays stored as raster map

imaginary=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) and constructs the real and imaginary Fourier components in frequency space.

Notes

The real and imaginary components are stored into the real and imaginary 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 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 raster=lsat7_2002_70
i.fft input=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 raster=lsat7_2002_70.real -p
d.mon x0
d.rast lsat7_2002_70.real
d.rast lsat7_2002_70.imag

References

See Also

i.cca, g.gui.iclass, i.ifft, i.pca

Authors

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

Source Code

Available at: i.fft source code (history)

Accessed: Saturday Nov 09 07:56:23 2024

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© 2003-2024 GRASS Development Team, GRASS GIS 8.4.0 Reference Manual

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