distance between images, pixel by pixel

I'm need to calculate the euclidean distance between two `cv::Mat` images in a pixel by pixel manner. Is there a function that does this? Specifically, I need the result to be of the form diff[i] = sqrt( (r1-r2)^2 + (g1-g2)^2 + (b1-b2)^2 ) where `diff` is a `Mat`. If there is no function, is there a simple way to calculate this? Thanks!