Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/image-1.0.15/fchcode.m b/octave_packages/image-1.0.15/fchcode.m
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+## Copyright (C) 2010 Andrew Kelly, IPS Radio & Space Services
+##
+## 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 3 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{fcc} = } fchcode (@var{bound})
+## Determine the Freeman chain code for a boundary.
+##
+## @code{fchcode} computes the Freeman chain code for the @var{n}-connected
+## boundary @var{bound}. @var{n} must be either 8 or 4.
+##
+## @var{bound} is a K-by-2 matrix containing the row/column coordinates of points
+## on the boundary. Optionally, the first point can be repeated as the last point,
+## resulting in a (K+1)-by-2 matrix.
+##
+## @var{fcc} is a structure containing the following elements.
+##
+## @example
+##  x0y0   = Row/column coordinates where the code starts (1-by-2) 
+##  fcc    = Freeman chain code (1-by-K)
+##  diff   = First difference of fcc (1-by-K)
+## @end example
+##
+## The code uses the following directions.
+##
+## @example
+##  3 2 1
+##  4 . 0
+##  5 6 7
+## @end example
+##
+## @seealso{bwboundaries}
+## @end deftypefn
+
+function fcc = fchcode (bound)
+
+  # ensure the boundary start and end points are the same
+  if (!isempty (bound) && !isequal (bound (1, :), bound (end, :)))
+    bound = [bound; bound(1, :)];
+  endif
+
+  # number of boundary points
+  n = max (0, rows (bound)-1);
+
+  # structure in which to return results
+  fcc = struct (\
+    'x0y0', zeros (1, n), \
+    'fcc',  zeros (1, n), \
+    'diff', zeros (1, n) \
+  );
+
+  # an empty boundary?
+  if (isempty (bound))
+    return;
+  endif
+
+  # direction map
+  dir = [3,  2,  1; \
+         4, NaN, 0; \
+         5,  6,  7];
+  
+  # coordinates
+  ROW = 1;
+  COL = 2;
+
+  # direction changes as row/column indexes into DIR
+  ch = 2 + diff (bound, 1, ROW);
+  
+  # starting point
+  fcc.x0y0 = bound (1, :);
+
+  # chain code
+  fcc.fcc = dir (sub2ind (size (dir), ch (:, ROW), ch (:, COL)))';
+
+  # chain code difference
+  fcc.diff = mod (diff ([fcc.fcc, fcc.fcc(1)]), 8);
+endfunction