1i.ifft(1)                     Grass User's Manual                    i.ifft(1)
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NAME

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

9       imagery
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SYNOPSIS

12       i.ifft
13       i.ifft help
14       i.ifft   real_image=string  imaginary_image=string  output_image=string
15       [--overwrite]  [--verbose]  [--quiet]
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17   Flags:
18       --overwrite
19           Allow output files to overwrite existing files
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21       --verbose
22           Verbose module output
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24       --quiet
25           Quiet module output
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27   Parameters:
28       real_image=string
29           Input raster map (image fft, real part)
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31       imaginary_image=string
32           Input raster map (image fft, imaginary part
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34       output_image=string
35           Output inverse raster map after IFFT
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DESCRIPTION

38       i.ifft is an image processing program based on the algorithm  given  by
39       Frigo  et  al. (1998), that converts real and imaginary frequency space
40       images (produced by i.fft) into a normal image.
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NOTES

43       The current mask is respected when reading the real and imaginary  com‐
44       ponent  files;   thus,  creating a mask is a primary step for selecting
45       the portion of the frequency space data to be included in  the  inverse
46       transform.  The GRASS program r.digit can be used to create masks while
47       viewing the real or imaginary component image.  Alternatively  r.circle
48       can be used to generate high-, low- and donut filters specifying the DC
49       point as circle/ring center.  When i.ifft is  executed,  it  (automati‐
50       cally) uses the same GRASS region definition setting that was used dur‐
51       ing the original transformation done with i.fft.
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53       The real and imaginary components are read from arrays  of  doubles  in
54       the  cell_misc  directory  (produced  by the forward transform program,
55       i.fft), and the reconstructed image will preserve the cell value  scal‐
56       ing  of  the  original  image  processed  by  i.fft.  No color table is
57       assigned to the output map;  one should be created before  viewing  the
58       output_image.
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SEE ALSO

61       M.  Frigo  and S. G. Johnson (1998): "FFTW: An Adaptive Software Archi‐
62       tecture for the FFT". See www.FFTW.org: FFTW is a C subroutine  library
63       for  computing  the  Discrete  Fourier  Transform  (DFT) in one or more
64       dimensions, of both real and complex data, and of arbitrary input size.
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66       Remote Sensing Digital Image Analysis, by John A.  Richards,  Springer-
67       Verlag, 1986.
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69       Personal  communication,  between program author and Ali R. Vali, Space
70       Research Center, University of Texas, Austin, 1990.
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72       i.cca, i.class, i.fft, i.pca, r.circle
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AUTHOR

75       David Satnik, GIS Laboratory, Central Washington University
76       Glynn Clements (FFTW support)
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78       Last changed: $Date: 2006-04-13 20:50:10 +0200 (Thu, 13 Apr 2006) $
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80       Full index
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82       © 2003-2008 GRASS Development Team
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86GRASS 6.3.0                                                          i.ifft(1)