smoothPolyline

SMOOTHPOLYLINE Smooth a polyline using local averaging.

   RES = smoothPolygon(POLY, M)
   POLY contains the polyline vertices, and M is the size of smoothing
   (given as the length of the convolution window).
   Extremities of the polyline are smoothed with reduced window (last and
   first vertices are kept identical, second and penultimate vertices are
   smoothed with 3 values, etc.).

   Example
     img = imread('circles.png');
     img = imfill(img, 'holes');
     contours = bwboundaries(img');
     poly = contours{1}(201:500,:);
     figure; drawPolyline(poly, 'b'); hold on;
     poly2 = smoothPolyline(poly, 21);
     drawPolygon(poly2, 'm');

   See also
     polygons2d, smoothPolygon, simplifyPolyline, resamplePolyline

0001 function res = smoothPolyline(poly, M)
0002 %SMOOTHPOLYLINE Smooth a polyline using local averaging.
0003 %
0004 %   RES = smoothPolygon(POLY, M)
0005 %   POLY contains the polyline vertices, and M is the size of smoothing
0006 %   (given as the length of the convolution window).
0007 %   Extremities of the polyline are smoothed with reduced window (last and
0008 %   first vertices are kept identical, second and penultimate vertices are
0009 %   smoothed with 3 values, etc.).
0010 %
0011 %   Example
0012 %     img = imread('circles.png');
0013 %     img = imfill(img, 'holes');
0014 %     contours = bwboundaries(img');
0015 %     poly = contours{1}(201:500,:);
0016 %     figure; drawPolyline(poly, 'b'); hold on;
0017 %     poly2 = smoothPolyline(poly, 21);
0018 %     drawPolygon(poly2, 'm');
0019 %
0020 %   See also
0021 %     polygons2d, smoothPolygon, simplifyPolyline, resamplePolyline
0022  
0023 % ------
0024 % Author: David Legland
0025 % e-mail: david.legland@grignon.inra.fr
0026 % Created: 2015-02-17,    using Matlab 8.4.0.150421 (R2014b)
0027 % Copyright 2015 INRA - Cepia Software Platform.
0028 
0029 % compute the number of elements before and after
0030 M1 = floor((M - 1) / 2);
0031 M2 = ceil((M - 1) / 2);
0032 
0033 % create convolution vector
0034 v2 = ones(M, 1) / M;
0035 
0036 % apply filtering on central part of the polyline
0037 res(:,1) = conv(poly(:,1), v2, 'same');
0038 res(:,2) = conv(poly(:,2), v2, 'same');
0039 
0040 % need to recompute the extremities
0041 for i = 1:M1
0042     i2 = 2 * i - 1;
0043     res(i, 1) = mean(poly(1:i2, 1));
0044     res(i, 2) = mean(poly(1:i2, 2));
0045 end
0046 for i = 1:M2
0047     i2 = 2 * i - 1;
0048     res(end - i + 1, 1) = mean(poly(end-i2+1:end, 1));
0049     res(end - i + 1, 2) = mean(poly(end-i2+1:end, 2));
0050 end