## [f4e068]: inst / fchcode.m  Maximize  Restore  History

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 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88``` ```## 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 . ## -*- 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 ```

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