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histeq.m

## Copyright (C) 2000  Kai Habel
##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; If not, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} @var{J} = histeq (@var{I}, @var{n})
## Histogram equalization of a gray-scale image. The histogram contains
## @var{n} bins, which defaults to 64.
##
## @var{I}: Image in double format, with values from 0.0 to 1.0
##
## @var{J}: Returned image, in double format as well
## @seealso{imhist}
## @end deftypefn

## Author:  Kai Habel <kai.habel@gmx.de>
## Date:    08. August 2000
## Modified-by: Jonas Wagner <j.b.w@gmx.ch>
## Date:        11. February 2008

function J = histeq (I, n)
  if (nargin == 0)
    print_usage();
  elseif (nargin == 1)
    n = 64;
  endif

  [r,c] = size(I); 
  I = mat2gray(I);
  [X,map] = gray2ind(I, n);
  [nn,xx] = imhist(I, n);
  Icdf = 1 / prod(size(I)) * cumsum(nn);
  J = reshape(Icdf(X),r,c);
  plot(Icdf,'b');
  legend( 'Image Cumulative Density Function');
endfunction

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