fft2D - Forward 2-D fast Fourier transform

Name

		fft2D - Forward 2-D fast Fourier transform

Author

INFO:	David E. Harris, Georgia Tech Research Institute
SOURCE FILE:	fracgen.c

Type

	filter

Inputs

		field 2D uniform any-2^n-size scalar any-data
		(a square array with dimensions = 2^n, n >= 2, n = integer)

Outputs

	field 2D uniform same-2^n-size 2-vector float
		field 2D uniform same-2^n-size scalar byte (optional)

Parameters

     Name		Type	Default	
		Center		toggle	off

Description

	This module takes the forward two dimensional fast Fourier transform
of a square array whose dimensions are integer powers of two.  As a practical
matter, realize that the result is a field with twice the number of values
(real and imaginary components) and each is a floating point number.  The
second output is a grayscale byte field which represents the log(1+magnitude)
of the FFT.  The log(1+magnitude) plot shows more detail than a plot of just
the magnitude.  The companion module to this one is the inverse FFT module
ifft2D.
   Center	- This toggle switch will place the dc value of the Fourier
		  transform in the center of the output field.  The default is
		  for the (0,0) point to be in the upper left corner.
		  Centering the transform will produce a more intuitive picture
		  if the RMS value of the transform is viewed as an image.  See
	 	  the example.
	

Example

This network reads in a field, performs the FFT and displays both the
magnitude plot and the log(1+magnitude) plot for comparison.
	
                          READ FIELD
                              |
                            FFT2D  <--- choose CENTER
      ______________________|   |____________
      |                                     |
      |       Extract channel 0|  __________|_________   |Extract channel 1
      |                        V  |                  |   V
  COLORIZER                EXTRACT SCALAR     EXTRACT SCALAR
      |                           |                  |
DISPLAY IMAGE                     |______   _________|
                                        |   |
                                      FIELD MATH  <--- choose RMS
                                           |
                                       COLORIZER
                                           |
                                     DISPLAY IMAGE

See also

 IFFT2D.