1i.ifft(1) Grass User's Manual i.ifft(1)
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6 i.ifft - Inverse Fast Fourier Transform (ifft) for image processing.
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9 imagery
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12 i.ifft
13 i.ifft help
14 i.ifft real_image=string imaginary_image=string output_image=string
15 [--overwrite]
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17 Flags:
18 --overwrite
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20 Parameters:
21 real_image=string
22 input raster file (image fft, real part)
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24 imaginary_image=string
25 input raster file (image fft, imaginary part
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27 output_image=string
28 output inverse raster file after ifft
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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.
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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.
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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.
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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.
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59 Remote Sensing Digital Image Analysis, by John A. Richards, Springer-
60 Verlag, 1986.
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62 Personal communication, between program author and Ali R. Vali, Space
63 Research Center, University of Texas, Austin, 1990.
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65 i.cca, i.class, i.fft, i.pca, r.circle
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68 David Satnik, GIS Laboratory, Central Washington University
69 Glynn Clements (FFTW support)
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71 Last changed: $Date: 2006/04/13 18:50:10 $
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73 Full index
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77GRASS 6.2.2 i.ifft(1)