problem with ssim function

i've divided the image into overlapping blocks and size of each block is 2x2. but when i used the ssim function it shows the result as

       -inf

why so?

like if

        a=[191 161;198 197]

        b=[201 191; 166 195]

       mssim=ssim(a,b);

       the result produced is -inf

plz help me to do so

Answer 1

[Iman Ansari]

Hi. It's default window:

window = fspecial('gaussian', 11, 1.5);

If input images has smaller size than 11*11 (it's window size), the output became -Inf. You may change default window:

a=[191 161;198 197]
b=[201 191; 166 195]
K(1) = 0.01;          % default settings
K(2) = 0.03;          %
window = ones(2);
mssim = ssim(a,b, K, window);