Error mapping between two images

Hi, I have this task to show the error mapping between reference and distorted image. For example,

ref = imread('pout.tif');
A = imnoise(ref,'salt & pepper', 0.02);
peaksnr = psnr(A,ref);

This code will get me the value of psnr. Is it possible for me to display the error mapping between the two images? So i can see the errors detected by PSNR method.

[KALYAN ACHARJYA]

error=A-ref;
imshow(error);

Or MSE?

"So i can see the errors detected by PSNR method".

Can you elaborate more?