function [d]=subtract(s1,s2);
ai=double(s1);
bi=double(s2);
a=size(ai);
b=size(bi);
if a(1)<b(1)
ai=[ai;zeros(b(1)-a(1),a(2))];
else
bi=[bi;zeros(a(1)-b(1),b(2))];
end
a=size(ai);
b=size(bi);
if a(2)<b(2)
ai=[ai zeros(a(1),b(2)-a(2))];
else
bi=[bi zeros(b(1),a(2)-b(2))];
end
d=ai-bi; % to find the difference
d=d+min(min(d));
d = (d/(max(max(d))))*255;
% figure
% imshow(d,[]);