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im2bw.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{BW}= im2bw (@var{I},threshold)
## @deftypefnx {Function File} @var{BW}= im2bw (@var{X},@var{cmap},threshold)
## Converts image data types to a black-white (binary) image.
## The treshold value should be in the range [0,1].
## @end deftypefn

## Author:  Kai Habel <kai.habel@gmx.de>
## Date:    19. March 2000

function BW = im2bw (img, a, b)
  if (nargin < 2 || nargin > 3)
    usage("im2bw: number of arguments must be 2 or 3");
  endif
  
  ## Convert img to gray scale
  if (isrgb(img))
    img = rgb2gray(img);
    if (nargin != 2)
      error("im2bw: two input arguments must be given when the image is a color image");
    endif
    t = a;
  elseif (isind (img) && ismatrix(a) && columns (a) == 3)
    img = ind2gray (img, a);
    if (nargin != 3)
      error("im2bw: three input arguments must be given when the image is indexed");
    endif
    t = b;
  elseif (isgray(img))
    if (nargin != 2)
      error("im2bw: two input arguments must be given when the image is gray scale");
    endif
    t = a;
  else
    error ("im2bw: first input argument must be an image");
  endif

  ## Do the thresholding
  if (isscalar (t))
    if (t < 0 || t > 1)
      error("im2bw: threshold must be in the interval [0, 1]");
    endif
    switch (class(img))
      case {"double", "single"}
        BW = (img >= t);
      case {"uint8"}
        BW = (img >= 255*t);
      case {"uint16"}
        BW = (img >= 65535*t);
      otherwise
        error("im2bw: unsupport image class");
    endswitch
  else
    error ("im2bw: threshold value must be scalar");
  endif

endfunction

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