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From: ImageAnalyst <imageanalyst@mailinator.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: SNR and imnosie
Date: Thu, 2 Jul 2009 10:30:10 -0700 (PDT)
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On Jul 2, 1:03 pm, "Alan B" <mongui...@yahoo.com> wrote:
> "Rami AbouSleiman" <rdabo...@oakland.edu> wrote in message <h2im2t$cg...@fred.mathworks.com>...
> > Image analyst,
>
> > BTW you don't need ./ since they are the same size.
>
> this would have been a quick way for you to (fail to) verify your own declaration:
>
> a=rand(2); b=rand(2);
> a/b, a./b

--------------------------------------------------------------------------
Rami:
I just want to re-emphasize Alan's note.  Alan and I are right and you
are mistaken.  You do need the dot slash - and the matching or non-
matching size is not the reason why.

Also, it depends on how you define noise.  If you just say that noise
is the observed distance between your actual signal and your true
signal, then you can use this definition
noise = mean(mean(abs(noisyImage - trueImage)));
Note the absolute value in there - otherwise your noise will be close
to zero.  If you want to say the noise is the standard deviation of
the differences between your noisy pixel values and your true values,
then you might use this:
noiseOnly = abs(noisyImage - trueImage);
noise = std(noiseOnly(:));
Or you could use the RMS (root mean square) definition for your
noise.  Something like
squaredImage = noiseOnly .^ 2  % Note the dot.
RMS = sqrt(mean(mean(squaredImage)));  % I think that's it.

Good luck,
ImageAnalyst