Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / image-1.0.15 / applylut.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{A} = } applylut (@var{BW},@var{LUT})
+## Uses lookup tables to perform a neighbour operation on binary images.
+##
+## A = applylut(BW,LUT) returns the result of a neighbour operation
+## using the lookup table @var{LUT} which can be created by makelut.
+##
+## It first computes a matrix with the index of each element in the
+## lookup table. To do this, it convolves the original matrix with a
+## matrix which assigns each of the neighbours a bit in the resulting
+## index. Then @var{LUT} is accessed to compute the result.
+##
+## @seealso{makelut}
+## @end deftypefn
+
+## Author:  Josep Mones i Teixidor <jmones@puntbarra.com>
+
+function A = applylut(BW, LUT)
+  if (nargin != 2)
+    usage ("A = applylut(BW, LUT)");
+  endif
+
+  nq=log2(length(LUT));
+  n=sqrt(nq);
+  if (floor(n)!=n)
+    error ("applylut: LUT length is not as expected. Use makelut to create it.");
+  endif
+  w=reshape(2.^[nq-1:-1:0],n,n);
+  A=LUT(filter2(w,BW)+1);
+endfunction
+
+%!demo
+%! lut = makelut (inline ('sum (x (:)) >= 3', 'x'), 3);
+%! S = applylut (eye (5), lut);
+%! disp (S)
+%! ## Everything should be 0 despite a diagonal which
+%! ## doesn't reach borders.
+
+
+%!assert(prod(applylut(eye(3),makelut(inline('x(1,1)==1','x'),2))==eye(3))==1); % 2-by-2 test
+%!assert(prod(applylut(eye(3),makelut(inline('x(2,2)==1','x'),3))==eye(3))==1); % 3-by-3 test
+%!assert(prod(applylut(eye(3),makelut(inline('x(3,3)==1','x'),3))== \
+%!           applylut(eye(3),makelut(inline('x(2,2)==1','x'),2)))==1);
+
+
+
+