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%By: LiuYu %Course: Digital Watermarking %Project: Calculates the PSNR (Peak Signal to Noise Ratio) % of images A and A', both of size NxN function [PSNR] = psnr(I,II) % convert to doubles x=double(I); X=double(II); N=size(x,1); PSNR=10*log10(N*N*255^2/sum(sum((x-X).^2))) return