if i normalize signal power of noisy image

I is original image and 'n' is noise image and it add in I to generate noisy image('mix'),means

    mix=I+n;

if i normalize signal power of noisy image as mean2(I) means

   P(signal)=mean(I)

if i normalize noise power of noisy image as std2(n) means

   P(noise)=std2(n)

then i define normalized snr as

    snr=P(signal)/P(noise)

is this problematic or right?

I have studied snr=mean(I./n),but this is another way

Answer 1

[Image Analyst]

That's not correct. You're better off doing the pixel by pixel ratio and then taking the mean, like your latter method. Mathematically they are not the same.