Sliding window in 2 images to create a third

Dear Matlab people.

I have 2 images or lets say 2 matrices of the same size with values ranging from 0-1. I need to apply different window sizes (3x3, 21x21) and with in these windows applx the following formula. I1 is the image 1 or matrix 1 and I2 is the matrix 2. Please ignore the * in the formula, here it represents something else.

Answer 1

[Nirja Mehta]

 i1 = randn([100 100]);
 i2 = randn([100 100]);
 R = 3;
 C = 21;
 num = 0;

 for i = 1:R
    for j = 1:C
        num = num + abs(i1(i,j)*i2(i,j));
    end
 end

You can calculate the denominator, likewise.