NAME¶
i.ifft - Inverse Fast Fourier Transform (IFFT) for image
processing.
KEYWORDS¶
imagery, FFT
SYNOPSIS¶
i.ifft
i.ifft help
i.ifft real_image=
name imaginary_image=
name
output_image=
name [--
overwrite] [--
verbose]
[--
quiet]
Flags:¶
- --overwrite
-
Allow output files to overwrite existing files
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
Parameters:¶
- real_image=name
-
Name of input raster map (image fft, real part)
- imaginary_image=name
-
Name of input raster map (image fft, imaginary part
- output_image=name
-
Name for output raster map
DESCRIPTION¶
i.ifft 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
i.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
program
r.digit can be used to create masks while viewing the real or
imaginary component image. Alternatively
r.circle can be used to
generate high-, low- and donut filters specifying the DC point as circle/ring
center. When
i.ifft is executed, it (automatically) uses the same GRASS
region definition setting that was used during the original transformation
done with
i.fft.
The real and imaginary components are read from arrays of doubles in the
cell_misc directory (produced by the forward transform program,
i.fft), and the reconstructed image will preserve the cell value
scaling of the original image processed by
i.fft. No color table is
assigned to the output map; one should be created before viewing the
output_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.
Remote Sensing Digital Image Analysis, 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)
Last changed: $Date: 2011-11-08 10:42:51 +0100 (Tue, 08 Nov 2011) $
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