All result is zero !

Hello, I want write this formula but all result is zero :(

input = imread('cameraman.tif');
[m , n] = size(input);
L = 255;
Xmax = L - 1 ; 
Xc = 0.5;
Fe = 2;
Fd = 30;
Pmn = ones(m,n);
Pmn = double(Pmn);
for i = 1:m
    for j = 1:n
        Xmn = input(i,j);
        Pmn(i,j)=1/((1+((Xmax-Xmn)/Fd)).^Fe);
    end
end

Answer 1

[Azzi Abdelmalek]

Use

Xmn = double(input(i,j))