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thin_zhangSuen.m
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thin_zhangSuen.m
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function [thin_image] = thin_zhangSuen(binary_image)
%THIN_ZHANGSUEN
% Step One：循环所有前景像素点，对符合如下条件的像素点标记为删除：
% 1. 2 <= N(p1) <=6
% 2. S(P1) = 1
% 3. P2 P4 P6 至少有1个为1
% 4. P4 P6 P8 至少有1个为1
% P9 P2 P3
% P8 P1 P4
% P7 P6 P5
% 其中，N(P1)表示8个邻居中为1的数目
% S(P1)表示从P2-P9-P2（顺时针）转一圈，从0到1变化的次数
% Step Two：循环所有前景像素点，对符合如下条件的像素点标记为删除：
% 1. 2 <= N(p1) <=6
% 2. S(P1) = 1
% 3. P2 P4 P8 至少有1个为1
% 4. P2 P6 P8 至少有1个为1
% https://blog.csdn.net/Ibelievesunshine/article/details/105069015
height = size(binary_image, 1);
width = size(binary_image, 2);
% inverse, 算法把0作为前景，1作为后景
thin_image = binary_image;
thin_image = 1 - thin_image;
while true
s1 = [];
s2 = [];
% Step 1
for i = 2 : height - 1
for j = 2 : width - 1
% 不是前景点不理会
if thin_image(i, j) > 0
continue;
end
% condition 1
flag1 = sum(thin_image(i - 1 : i + 1, j - 1 : j + 1), 'all');
if flag1 < 2 || flag1 > 6
continue;
end
% condition 2
flag2 = 0;
if(thin_image(i - 1, j + 1) - thin_image(i - 1, j) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i, j + 1) - thin_image(i - 1, j + 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i + 1, j + 1) - thin_image(i, j + 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i + 1, j) - thin_image(i + 1, j + 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i + 1, j - 1) - thin_image(i + 1, j) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i, j - 1) - thin_image(i + 1, j - 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i - 1, j - 1) - thin_image(i, j - 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i - 1, j) - thin_image(i - 1, j - 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i - 1, j) - thin_image(i - 1, j - 1) == 1)
flag2 = flag2 + 1;
end
if flag2 ~= 1
continue;
end
% condition 3
if(thin_image(i - 1, j) + thin_image(i, j + 1) + thin_image(i + 1, j) < 1)
continue;
end
% condition 4
if(thin_image(i, j + 1) + thin_image(i + 1, j) + thin_image(i, j - 1) < 1)
continue;
end
s1 = [s1; [i, j]];
end
end
for k = 1 : size(s1, 1)
thin_image(s1(k, 1), s1(k, 2)) = 1;
end
% Step 2
for i = 2 : height - 1
for j = 2 : width - 1
% 不是前景点不理会
if thin_image(i, j) > 0
continue;
end
% condition 1
flag1 = sum(thin_image(i - 1 : i + 1, j - 1 : j + 1), 'all');
if flag1 < 2 || flag1 > 6
continue;
end
% condition 2
flag2 = 0;
if(thin_image(i - 1, j + 1) - thin_image(i - 1, j) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i, j + 1) - thin_image(i - 1, j + 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i + 1, j + 1) - thin_image(i, j + 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i + 1, j) - thin_image(i + 1, j + 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i + 1, j - 1) - thin_image(i + 1, j) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i, j - 1) - thin_image(i + 1, j - 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i - 1, j - 1) - thin_image(i, j - 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i - 1, j) - thin_image(i - 1, j - 1) == 1)
flag2 = flag2 + 1;
end
if(thin_image(i - 1, j) - thin_image(i - 1, j - 1) == 1)
flag2 = flag2 + 1;
end
if flag2 ~= 1
continue;
end
% condition 3
if(thin_image(i - 1, j) + thin_image(i, j + 1) + thin_image(i, j - 1) < 1)
continue;
end
% condition 4
if(thin_image(i - 1, j) + thin_image(i + 1, j) + thin_image(i, j - 1) < 1)
continue;
end
s2 = [s2; [i, j]];
end
end
for k = 1 : size(s2, 1)
thin_image(s2(k, 1), s2(k, 2)) = 1;
end
% 如果两步中都没有点要删除，结束循环
if size(s1, 1) == 0 && size(s2, 1) == 0
break;
end
end
thin_image = 1 - thin_image;
end