function psnr= PSNR(X,Y)
[M,N]=size(X);
m=0;
X=cast(X,'double');
Y=cast(Y,'double');
for i=1:M
  for j=1:N
      m=m+((X(i,j)-Y(i,j))^2);
  end
end
m=m/(M*N);
psnr=10*log10(255*255/m);