bound2four.m

冈萨雷斯的经典教材数字图像处理的matlab版源代码

function rc_new = bound2four(rc)
%BOUND2FOUR Convert 8-connected boundary to 4-connected boundary.
%   RC_NEW = BOUND2FOUR(RC) converts an eight-connected boundary to a
%   four-connected boundary.  RC is a P-by-2 matrix, each row of
%   which contains the row and column coordinates of a boundary
%   pixel.  BOUND2FOUR inserts new boundary pixels wherever there is
%   a diagonal connection.

%   Copyright 2002-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins
%   Digital Image Processing Using MATLAB, Prentice-Hall, 2004
%   $Revision: 1.4 $  $Date: 2003/11/21 14:20:21 $

if size(rc, 1) > 1
   % Phase 1: remove diagonal turns, one at a time until they are all gone.
   done = 0;
   rc1 = [rc(end - 1, :); rc];
   while ~done
      d = diff(rc1, 1);
      diagonal_locations = all(d, 2);
      double_diagonals = diagonal_locations(1:end - 1) & ...
          (diff(diagonal_locations, 1) == 0);
      double_diagonal_idx = find(double_diagonals);
      turns = any(d(double_diagonal_idx, :) ~= ...
                  d(double_diagonal_idx + 1, :), 2);
      turns_idx = double_diagonal_idx(turns);
      if isempty(turns_idx)
         done = 1;
      else
         first_turn = turns_idx(1);
         rc1(first_turn + 1, :) = (rc1(first_turn, :) + ...
                                   rc1(first_turn + 2, :)) / 2;
         if first_turn == 1
            rc1(end, :) = rc1(2, :);
         end
      end
   end
   rc1 = rc1(2:end, :);
end

% Phase 2: insert extra pixels where there are diagonal connections.

rowdiff = diff(rc1(:, 1));
coldiff = diff(rc1(:, 2));

diagonal_locations = rowdiff & coldiff;
num_old_pixels = size(rc1, 1);
num_new_pixels = num_old_pixels + sum(diagonal_locations);
rc_new = zeros(num_new_pixels, 2);

% Insert the original values into the proper locations in the new RC
% matrix.
idx = (1:num_old_pixels)' + [0; cumsum(diagonal_locations)];
rc_new(idx, :) = rc1;

% Compute the new pixels to be inserted.
new_pixel_offsets = [0 1; -1 0; 1 0; 0 -1];
offset_codes = 2 * (1 - (coldiff(diagonal_locations) + 1)/2) + ...
    (2 - (rowdiff(diagonal_locations) + 1)/2);
new_pixels = rc1(diagonal_locations, :) + ...
    new_pixel_offsets(offset_codes, :); 

% Where do the new pixels go?
insertion_locations = zeros(num_new_pixels, 1);
insertion_locations(idx) = 1;
insertion_locations = ~insertion_locations;

% Insert the new pixels.
rc_new(insertion_locations, :) = new_pixels;