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 01:42:51 -0800 (Tue, 08 Nov 2011) $

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       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                       i.ifft(1grass)