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dilate.m

## Copyright (C) 2004 Josep Mones i Teixidor
##
## 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{BW2} = } dilate (@var{BW1},@var{SE})
## @deftypefnx {Function File} {@var{BW2} = } dilate (@var{BW1},@var{SE},@var{alg})
## @deftypefnx {Function File} {@var{BW2} = } dilate (@var{BW1},@var{SE},...,@var{n})
## Perform a dilation morphological operation on a binary image.
##
## BW2 = dilate(BW1, SE) returns a binary image with the result of a dilation
## operation on @var{BW1} using neighbour mask @var{SE}.
##
## For each point in @var{BW1}, dilate search its neighbours (which are
## defined by setting to 1 their in @var{SE}). If any of its neighbours
## is on (1), then pixel is set to 1. If all are off (0) then it is set to 0.
##
## Center of @var{SE} is calculated using floor((size(@var{SE})+1)/2).
##
## Pixels outside the image are considered to be 0.
##
## BW2 = dilate(BW1, SE, alg) returns the result of a dilation operation 
## using algorithm @var{alg}. Only 'spatial' is implemented at the moment.
##
## BW2 = dilate(BW1, SE, ..., n) returns the result of @var{n} dilation
## operations on @var{BW1}.
##
## @seealso{erode}
## @end deftypefn

## Author:  Josep Mones i Teixidor <jmones@puntbarra.com>

function BW2 = dilate(BW1, SE, a, b)
  alg='spatial';
  n=1;
  if (nargin < 1 || nargin > 4)
    usage ("BW2 = dilate(BW1, SE [, alg] [, n])");
  endif
  if nargin ==  4
    alg=a;
    n=b;
  elseif nargin == 3
    if ischar(a)
      alg=a;
    else
      n=a;
    endif
  endif

  if !strcmp(alg, 'spatial')
    error("dilate: alg not implemented.");
  endif

  # "Binarize" BW1, just in case image is not [1,0]
  BW1=BW1!=0;

  for i=1:n
    # create result matrix
    BW1=filter2(SE,BW1)>0;
  endfor

  BW2=BW1;
endfunction

%!demo
%! dilate(eye(5),ones(2,2))
%! % returns a thick diagonal.



%!assert(dilate(eye(3),[1])==eye(3));     # using  as a mask returns the same value
%!assert(dilate(eye(3),[1,0,0])==[[0;0],eye(2);0,0,0]);
%!assert(dilate(eye(3),[1,0,0,0])==[[0;0],eye(2);0,0,0]); # test if center is correctly calculated on even masks



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