function f = contrast(filename)
a = imread(filename);
[rows cols] = size(a);
% imshow(a)
% syms r c k a
k = zeros(rows,cols);

for r = 1:rows
    for c = 1:cols
%         a(r,c) = 26;
%         new = 26/255;
%           a(r,c)
%           (double)(a(r,c))
         
          k(r,c) = double(a(r,c))/double(255);
          k(r,c) = (((k(r,c)-0.5)*5)+0.5)*255;

        if k(r,c) > 255
            k(r,c) = 255;
        elseif k(r,c) < 0
            k(r,c) = 0;
        end
        k(r,c);
    end
end
f = k;