Zhang-Suen thinning algorithm in Matlab?????

I want to write a code Zhang-Suen thinning algorithm in matlab. Actally I had written the code but i dont know why it is entering in some sort of never ending loop.

My image is like a black part on the white background (White==1 and Black pixel ==0)

I am foolowing the steps given inthi link for the algorithm.

http://rosettacode.org/wiki/Zhang-Suen_thinning_algorithm

Can some one help me to implement it or any code for tis algo. in matlab.

My code is:--

Q is my binary image matrix;

 N=1; 

M=1;

while (M+N)~=0
     M=0;
     N=0;
for i=2:size(Q,1)-1
    for j=2:size(Q,2)-1
        Ap=0;
        Bp=0;
        if Q(i-1,j)==1 && Q(i-1,j+1)==0  %%p2 to p3    
            Ap=Ap+1;
        end
        if Q(i-1,j+1)==1 && Q(i,j+1)==0  %%p3 to p4
            Ap=Ap+1;
        end
        if Q(i,j+1)==1 && Q(i+1,j+1)==0  %%p4 to p5
            Ap=Ap+1;
        end
        if Q(i+1,j+1)==1 && Q(i+1,j)==0  %%p5 to p6
            Ap=Ap+1;
        end
        if Q(i+1,j)==1 && Q(i+1,j-1)==0  %%p6 to p7
            Ap=Ap+1;
        end
        if Q(i+1,j-1)==1 && Q(i,j-1)==0  %%p7 to p8
            Ap=Ap+1;
        end
        if Q(i,j-1)==1 && Q(i-1,j-1)==0  %%p8 to p9
            Ap=Ap+1;
        end
        if Q(i-1,j-1)==1 && Q(i,j)==0    %%p9 to p2
            Ap=Ap+1;
        end
        if Q(i-1,j-1)==0      %%p9
            Bp=Bp+1;
        end
        if Q(i-1,j)==0      %%p2
            Bp=Bp+1;
        end
        if Q(i-1,j+1)==0    %%p3
            Bp=Bp+1;
        end
        if Q(i,j-1)==0  %%p8
            Bp=Bp+1;
        end
        if Q(i,j+1)==0      %%p4
            Bp=Bp+1;
        end
        if Q(i+1,j-1)==0        %%p7
            Bp=Bp+1;
        end
        if Q(i+1,j)==0      %%p6
            Bp=Bp+1;
        end
        if Q(i+1,j+1)==0      %%p5
            Bp=Bp+1;
        end
        if Q(i,j)==0
            if 2<=Bp<=6
                if Ap==1
                    if Q(i-1,j)==1 ||Q(i+1,j)==1 ||Q(i,j+1)==1
                        if Q(i,j-1)==1 ||Q(i+1,j)==1 ||Q(i,j+1)==1
                            if Q(i+1,j-1)~=1
                                Q(i,j)==1;
                                N=N+1;
                            end
                        end
                    end
                end
            end
        end
    end
end

for i=2:size(Q,1)-1
    for j=2:size(Q,2)-1
        Ap=0;
        Bp=0;
        if Q(i-1,j)==1 && Q(i-1,j+1)==0  %%p2 to p3
            Ap=Ap+1;
        end
        if Q(i-1,j+1)==1 && Q(i,j+1)==0  %%p3 to p4
            Ap=Ap+1;
        end
        if Q(i,j+1)==1 && Q(i+1,j+1)==0  %%p4 to p5
            Ap=Ap+1;
        end
        if Q(i+1,j+1)==1 && Q(i+1,j)==0  %%p5 to p6
            Ap=Ap+1;
        end
        if Q(i+1,j)==1 && Q(i+1,j-1)==0  %%p6 to p7
            Ap=Ap+1;
        end
        if Q(i+1,j-1)==1 && Q(i,j-1)==0  %%p7 to p8
            Ap=Ap+1;
        end
        if Q(i,j-1)==1 && Q(i-1,j-1)==0  %%p8 to p9
            Ap=Ap+1;
        end
        if Q(i-1,j-1)==1 && Q(i,j)==0    %%p9 to p2
            Ap=Ap+1;
        end
        if Q(i-1,j-1)==0      %%p9
            Bp=Bp+1;
        end
        if Q(i-1,j)==0      %%p2
            Bp=Bp+1;
        end
        if Q(i-1,j+1)==0    %%p3
            Bp=Bp+1;
        end
        if Q(i,j-1)==0  %%p8
            Bp=Bp+1;
        end
        if Q(i,j+1)==0      %%p4
            Bp=Bp+1;
        end
        if Q(i+1,j-1)==0        %%p7
            Bp=Bp+1;
        end
        if Q(i+1,j)==0      %%p6
            Bp=Bp+1;
        end
        if Q(i+1,j+1)==0      %%p5
            Bp=Bp+1;
        end
        if Q(i,j)==0
            if 2<=Bp<=6
                if Ap==1
                    if Q(i-1,j)==1 ||Q(i,j-1)==1 ||Q(i,j+1)==1
                        if Q(i-1,j)==1 ||Q(i+1,j)==1 ||Q(i,j-1)==1
                            if Q(i+1,j-1)~=1
                                Q(i,j)==1;
                                N=N+1;
                            end

                          end
                      end
                  end
              end
          end
      end
  end
  end
  figure,imshow(Q),title('Thinning by Zang Suen Algo');

Answer 1

[Alexander Abramenko]

Assume black pixels are one and white pixels zero, and that the input image is a rectangular N by M array of ones and zeroes.

I=rgb2gray(imread('new.bmp'));
BW = not(im2bw(I));
imshow(not(BW),[]);
figure;
continue_it = 1;
while continue_it
BW_old=BW;
BW_del=zeros(size(BW));
for i=2:size(BW,1)-1
    for j = 2:size(BW,2)-1
        P = [BW(i,j) BW(i-1,j) BW(i-1,j+1) BW(i,j+1) BW(i+1,j+1) BW(i+1,j) BW(i+1,j-1) BW(i,j-1) BW(i-1,j-1) BW(i-1,j)];
        if P(2)*P(4)*P(6)==0 && P(4)*P(6)*P(8)==0 && sum(P(2:end-1))<=6 && sum(P(2:end-1)) >=2
            A = 0;
            for k = 2:size(P(:),1)-1
                if P(k) == 0 && P(k+1)==1
                    A = A+1;
                end%if
            end%for
            if (A==1)
                BW_del(i,j)=1;
            end%if
        end%if
    end%for
end%for

BW(find(BW_del==1))=0;

for i=2:size(BW,1)-1
    for j = 2:size(BW,2)-1
        P = [BW(i,j) BW(i-1,j) BW(i-1,j+1) BW(i,j+1) BW(i+1,j+1) BW(i+1,j) BW(i+1,j-1) BW(i,j-1) BW(i-1,j-1) BW(i-1,j)];
        if P(2)*P(4)*P(8)==0 && P(2)*P(6)*P(8)==0 && sum(P(2:end-1))<=6 && sum(P(2:end-1)) >=2
            A = 0;
            for k = 2:size(P(:),1)-1
                if P(k) == 0 && P(k+1)==1
                    A = A+1;
                end%if
            end%for
            if (A==1)
                BW_del(i,j)=1;
            end%if
        end%if
    end%for
end%for

BW(find(BW_del==1))=0;

if prod(BW_old(:)==BW(:))
   continue_it=0;
end%if

end%while
imshow(not(BW),[])

[UNNI KRISHNAN M S]

Dear Alexander,

Cud u kindly explain the working of this code line by line....???...pls help

Answer 2

[linbo jin]

Skeletonization by Zhang-Suen Thinning Algorithm, Python and Matlab Implementation: github code

[Nasreen Ehsan]

How we implement Huang Wan Liu thinning algorithm in Matlab?