Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / image-1.0.15 / erode.m

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+## 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} = } erode (@var{BW1},@var{SE})
+## @deftypefnx {Function File} {@var{BW2} = } erode (@var{BW1},@var{SE},@var{alg})
+## @deftypefnx {Function File} {@var{BW2} = } erode (@var{BW1},@var{SE},...,@var{n})
+## Perform an erosion morphological operation on a binary image.
+##
+## BW2 = erosion(BW1, SE) returns a binary image with the result of an erosion
+## operation on @var{BW1} using neighbour mask @var{SE}.
+##
+## For each point in @var{BW1}, erode searchs its neighbours (which are
+## defined by setting to 1 their in @var{SE}). If all neighbours
+## are on (1), then pixel is set to 1. If any is 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 = erode(BW1, SE, alg) returns the result of a erosion operation 
+## using algorithm @var{alg}. Only 'spatial' is implemented at the moment.
+##
+## BW2 = erosion(BW1, SE, ..., n) returns the result of @var{n} erosion
+## operations on @var{BW1}.
+##
+## @seealso{dilate}
+## @end deftypefn
+
+## Author:  Josep Mones i Teixidor <jmones@puntbarra.com>
+
+function BW2 = erode(BW1, SE, a, b)
+  alg='spatial';
+  n=1;
+  if (nargin < 1 || nargin > 4)
+    usage ("BW2 = erode(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("erode: alg not implemented.");
+  endif
+
+  # count ones in mask
+  thr=sum(SE(:));
+
+  # "Binarize" BW1, just in case image is not [1,0]
+  BW1=BW1!=0;
+
+  for i=1:n
+    # create result matrix
+    BW1=filter2(SE,BW1) == thr;
+  endfor
+
+  BW2=BW1;
+endfunction
+
+%!demo
+%! erode(ones(5,5),ones(3,3))
+%! % creates a zeros border around ones.
+
+
+
+%!assert(erode([0,1,0;1,1,1;0,1,0],[0,0,0;0,0,1;0,1,1])==[1,0,0;0,0,0;0,0,0]);
+%!assert(erode([0,1,0;1,1,1;0,1,0],[0,1;1,1])==[1,0,0;0,0,0;0,0,0]);
+
+