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, transformation, Fast Fourier Transform
10

SYNOPSIS

12       i.ifft
13       i.ifft --help
14       i.ifft  real=name  imaginary=name  output=name  [--overwrite]  [--help]
15       [--verbose]  [--quiet]  [--ui]
16
17   Flags:
18       --overwrite
19           Allow output files to overwrite existing files
20
21       --help
22           Print usage summary
23
24       --verbose
25           Verbose module output
26
27       --quiet
28           Quiet module output
29
30       --ui
31           Force launching GUI dialog
32
33   Parameters:
34       real=name [required]
35           Name of input raster map (image fft, real part)
36
37       imaginary=name [required]
38           Name of input raster map (image fft, imaginary part
39
40       output=name [required]
41           Name for output raster map
42

DESCRIPTION

44       i.ifft is an image processing program based on the algorithm  given  by
45       Frigo  et  al. (1998), that converts real and imaginary frequency space
46       images (produced by i.fft) into a normal image.
47

NOTES

49       The current mask is respected when reading the real and imaginary  com‐
50       ponent  files;   thus,  creating a mask is a primary step for selecting
51       the portion of the frequency space data to be included in  the  inverse
52       transform.   The  module  wxGUI  vector digitizer can be used to create
53       masks while viewing the real or  imaginary  component  image.  Alterna‐
54       tively  r.circle  can be used to generate high-, low- and donut filters
55       specifying the DC point as circle/ring center. When i.ifft is executed,
56       it  (automatically)  uses the same GRASS region definition setting that
57       was used during the original transformation done with i.fft.
58

SEE ALSO

60        i.cca, g.gui.iclass, i.fft, i.pca, r.circle, wxGUI vector digitizer
61

REFERENCES

63           ·   M. Frigo and S. G. Johnson (1998): "FFTW: An Adaptive  Software
64               Architecture  for  the FFT". See www.fftw.org: FFTW is a C sub‐
65               routine library for computing the  Discrete  Fourier  Transform
66               (DFT) in one or more dimensions, of both real and complex data,
67               and of arbitrary input size.
68
69           ·   Richards, J.A (1986): Remote Sensing  Digital  Image  Analysis,
70               Springer-Verlag, 1986.
71
72           ·   Personal communication, between program author and Ali R. Vali,
73               Space Research Center, University of Texas, Austin, 1990.
74

AUTHORS

76       David Satnik, GIS Laboratory, Central Washington University
77       Glynn Clements (FFTW support)
78
79       Last changed: $Date: 2014-11-01 11:07:51 +0100 (Sat, 01 Nov 2014) $
80

SOURCE CODE

82       Available at: i.ifft source code (history)
83
84       Main index | Imagery index | Topics index | Keywords index |  Graphical
85       index | Full index
86
87       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual
88
89
90
91GRASS 7.6.0                                                          i.ifft(1)
Impressum