Fastest way to compute distance between patches

Hi, for each pixel(x,y) of a given image: two squared patches P1, P2 on each side(left and right) are considered. Then, i have to compute the distance between each symetric elements of P1 and P2. I have implemented this but in a naïve way, so it is really very slow. I want to do it in a fast way.

Any help would be appreciated.

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/images/ref/immse.html