chain code for line

here is my question : in this image which I have attached , starting from (x,y) or (s,t)how can I write the chain code for the line ? what is proper idea to write its code ? a lot of thank for everyone help me or try to help .

Answer 1

[Walter Roberson]

http://www.mathworks.com/matlabcentral/fileexchange/29518-freeman-chain-code

[majed majed]

Thank you to your answer, I have traied it , but I didn't get the gall.

Answer 2

[Guillaume]

I've no idea what a chain code is, but if you're wanting to trace the path from (s,t) to (I,J) isn't it simply finding which of the eight neighbouring pixel is black, excluding pixels you've already been through.

currentrow = s;
currentcol = t;
path = [currentrow currentcol]
while currentrow ~= I && currentrow ~= J
     [neighbours(:, 1), neighbours(:, 2)] = find(img(currentrow-1:currentrow+1, currentcol-1:currentcol+1) & [1 1 1;1 0 1;1 1 1])); %ignoring edge issues here
     notvisited = ~ismember(neighbours, path, 'rows');
     path = [path; neighbours(notvisited)]; %assumes there's only ever one non-visited neighbour
     currentrow = neighbours(notvisited, 1);
     currentcol = neighbours(notvisited, 2);
end

[majed majed]

Thank you a lot , in my question if I start from any edge ,I don't know where is the other edge , so when I find the starting point (one of the edges) ,I need to extract the angle between current pixel and next pixel according to freeman chaincode edea ,suppose that the pixels inside line has just tow neighbors. that's it exactly what I want, thanks