1i.ifft(1)                     Grass User's Manual                    i.ifft(1)
2
3
4

NAME

6       i.ifft  - Inverse Fast Fourier Transform (ifft) for image processing.
7

KEYWORDS

9       imagery
10

SYNOPSIS

12       i.ifft
13       i.ifft help
14       i.ifft   real_image=string  imaginary_image=string  output_image=string
15       [--overwrite]
16
17   Flags:
18       --overwrite
19
20   Parameters:
21       real_image=string
22           input raster file (image fft, real part)
23
24       imaginary_image=string
25           input raster file (image fft, imaginary part
26
27       output_image=string
28           output inverse raster file after ifft
29

DESCRIPTION

31       i.ifft is an image processing program based on the algorithm  given  by
32       Frigo  et  al. (1998), that converts real and imaginary frequency space
33       images (produced by i.fft) into a normal image.
34

NOTES

36       The current mask is respected when reading the real and imaginary  com‐
37       ponent  files;   thus,  creating a mask is a primary step for selecting
38       the portion of the frequency space data to be included in  the  inverse
39       transform.  The GRASS program r.digit can be used to create masks while
40       viewing the real or imaginary component image.  Alternatively  r.circle
41       can be used to generate high-, low- and donut filters specifying the DC
42       point as circle/ring center.  When i.ifft is  executed,  it  (automati‐
43       cally) uses the same GRASS region definition setting that was used dur‐
44       ing the original transformation done with i.fft.
45
46       The real and imaginary components are read from arrays  of  doubles  in
47       the  cell_misc  directory  (produced  by the forward transform program,
48       i.fft), and the reconstructed image will preserve the cell value  scal‐
49       ing  of  the  original  image  processed  by  i.fft.  No color table is
50       assigned to the output map;  one should be created before  viewing  the
51       output_image.
52

SEE ALSO

54       M.  Frigo  and S. G. Johnson (1998): "FFTW: An Adaptive Software Archi‐
55       tecture for the FFT". See www.FFTW.org: FFTW is a C subroutine  library
56       for  computing  the  Discrete  Fourier  Transform  (DFT) in one or more
57       dimensions, of both real and complex data, and of arbitrary input size.
58
59       Remote Sensing Digital Image Analysis, by John A.  Richards,  Springer-
60       Verlag, 1986.
61
62       Personal  communication,  between program author and Ali R. Vali, Space
63       Research Center, University of Texas, Austin, 1990.
64
65       i.cca, i.class, i.fft, i.pca, r.circle
66

AUTHOR

68       David Satnik, GIS Laboratory, Central Washington University
69       Glynn Clements (FFTW support)
70
71       Last changed: $Date: 2006/04/13 18:50:10 $
72
73       Full index
74
75
76
77GRASS 6.2.2                                                          i.ifft(1)
Impressum