Fwd: [APML] Examples of Stacking Page

[Gil Shillcutt <astrocycle@yahoo.com>]

Frank,

In the example you show, you describe the improvement
in signal to noise ratio thusly:
"The other point is that it basically requires a
doubling of number of images to gain a not quite 2x
improvement in grain and detail (2x is subjective). So
the next iteration of this image will require 8 more
images to be added to the stack and the next one after
that will require 16 more (for a total of 32)."

Referring to the archives at:
http://astro.umsystem.edu/apml/search.html
pointed me to this, from a thread in '00:
http://astro.umsystem.edu/apml/ARCHIVES/MAY00/msg00805.html
What you find is that the signal of your image 
scales linearly with the number of images you add,
the noise scales as to the root sum of squares (RSS),
so that the signal-to-noise ratio (SNR) scales?
SNR = n / sqrt(n).  Your seat-of-the pants evaluation
was close, but this is the empirical answer.
So, if you want 2x SNR, you need to stack 4 images,
3x SNR, you need 9, etc.

-- Gil

--- "Franklin A. Holub" <lists@my-spot.com> wrote:
> From: "Franklin A. Holub" <lists@my-spot.com>
> To: <astro-photo@seds.org>
> Subject: [APML] Examples of Stacking Page
> Date: Thu, 23 May 2002 17:05:27 -0400
> Reply-to: astro-photo@seds.org
> 
>    I have put together a page that shows the effects
> and benefits of stacking astrophotos. The link is...
> 
> http://www.my-spot.com/stacking.htm
> 
> I put the images together a few months ago but never
> got around to making the page until today... Its in
> a kind of "beta" stage and suggestions are welcome!
> 
> Frank
> http://www.my-spot.com
> 
> 
> --  APML Archives at
> <http://astro.umsystem.edu/apml/>  ---
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