Re: [APML] Stacking negatives question

[Aplanatic@aol.com]

Bob Yen wrote:

> The above implies that:
>  
>   signal = nebula (or whatever object you're shooting)
>   noise = film-grain mottling in the sky-background area (i.e.,
>  noise-floor near shadow detail)
>  
>  signal-to-noise ratio = signal/noise is *increased* by "averaging out
>  the film-grain in the sky background", i.e. lessening the "noise"
>  denominator in signal/noise 
>  
>  I have a question for all of you.  How many of you believe this?
>  (including Jerry)

As an operational definition it looks OK to me.  Signal should add, 
"noise" due to film grain should add as RSS (root sum of the square, 
since it's more or less random).   Then stacking two negatives yields 
an SNR increase of 2/sqrt(2), or 1.41, or 3 dB, etc.  Are you going to 
tell us what you think?  If so, I'd like to hear it.  But if this is more 
Jerry bashing, count me entirely out.

Dave Rowe.     

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