I = imread('16.png') ;
[m,n] = size(I) ;
[y,x] = find(I) ;
% GEt mean
mx = mean(x) ; my = mean(y) ;
% Line 1
L1 = [repmat(mx,m,1) (1:m)'] ;
L2 = [(1:n)' repmat(my,n,1) ] ;
P = [L1(1,1) L1(1,2) ; L1(end,1) L1(end,2) ;L2(1,1) L2(1,2) ; L2(end,1) L2(end,2) ] ;
idx = knnsearch([x y],P) ;
imshow(I) ;
hold on
plot(x(idx),y(idx),'*r')
