## Copyright (C) 2000  Etienne Grossmann
##
## 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, write to the Free Software
## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

##       b = bwborder(im)
##
## b is the borders in the 0-1 matrix im. 4-neighborhood is considered.
## 
## A pixel is on the border if it is set in im, and it has at least one
## neighbor that is not set.

## Author:        Etienne Grossmann <etienne@cs.uky.edu>
## Last modified: January 2000

function b = bwborder(im)

[R,C]=size(im);

b = im & ...
    !([im(2:R,:) ;  zeros(1,C) ] & ...
      [zeros(1,C); im(1:R-1,:) ] & ...
      [im(:,2:C) ,  zeros(R,1) ] & ...
      [zeros(R,1),  im(:,1:C-1)] ) ;