smoothPolygon

SMOOTHPOLYGON Smooth a polygon using local averaging.

   RES = smoothPolygon(POLY, M)
   POLY contains the polygon vertices, and M is the size of smoothing
   (given as the length of the convolution window).


   Example
     img = imread('circles.png');
     img = imfill(img, 'holes');
     contours = bwboundaries(img');
     contour = contours{1};
     imshow(img); hold on; drawPolygon(contour, 'b');
     contourf = smoothPolygon(contour, 11);
     drawPolygon(contourf, 'm');

   See also
     polygons2d, smoothPolyline, simplifyPolygon, resamplePolygon

0001 function res = smoothPolygon(poly, M)
0002 %SMOOTHPOLYGON Smooth a polygon using local averaging.
0003 %
0004 %   RES = smoothPolygon(POLY, M)
0005 %   POLY contains the polygon vertices, and M is the size of smoothing
0006 %   (given as the length of the convolution window).
0007 %
0008 %
0009 %   Example
0010 %     img = imread('circles.png');
0011 %     img = imfill(img, 'holes');
0012 %     contours = bwboundaries(img');
0013 %     contour = contours{1};
0014 %     imshow(img); hold on; drawPolygon(contour, 'b');
0015 %     contourf = smoothPolygon(contour, 11);
0016 %     drawPolygon(contourf, 'm');
0017 %
0018 %   See also
0019 %     polygons2d, smoothPolyline, simplifyPolygon, resamplePolygon
0020  
0021 % ------
0022 % Author: David Legland
0023 % e-mail: david.legland@grignon.inra.fr
0024 % Created: 2015-02-17,    using Matlab 8.4.0.150421 (R2014b)
0025 % Copyright 2015 INRA - Cepia Software Platform.
0026 
0027 % compute the number of elements before and after
0028 M1 = floor((M - 1) / 2);
0029 M2 = ceil((M - 1) / 2);
0030 
0031 % repeat beginning and end of contour
0032 poly2 = [poly(end-M1+1:end, :) ; poly ; poly(1:M2,:)];
0033 
0034 % create convolution vector
0035 v2 = ones(M, 1) / M;
0036 
0037 % apply contour filtering
0038 res(:,1) = conv(poly2(:,1), v2, 'same');
0039 res(:,2) = conv(poly2(:,2), v2, 'same');
0040 
0041 % keep the interesting part
0042 res = res(M1+1:end-M2, :);