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


       imagery, FFT


       i.ifft help
       i.ifft  real_image=name imaginary_image=name output_image=name  [--overwrite]  [--verbose]

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of input raster map (image fft, real part)

           Name of input raster map (image fft, imaginary part

           Name for output raster map


       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


       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 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


       M. Frigo and S. G. Johnson (1998): "FFTW: An Adaptive Software Architecture for the  FFT".
       See  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,


       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