how can we PSNR ratio for images?

what is the coding for comparing two gray images using psnr ratio.i want to select the suitable filter for image processing. using some coding for psnr ratio which i got from internet are very confusing and didn't produce any results.please send me the possible codings for finding psnr.

Answer 1

[Nitin]

Check out the link on file exchange to compute the PSNR between 2 images