Subs and Duplicates

[Coco]

Hi, rather than take 20 x subs at the same exposure etc, why cant you just duplicate the image 20 x in Photoshop. Rename them 1,2,3 etc?

You wise old badgers will probably have the reason...

.

Guy

[brendant]

Sounds like a good idea but unfourtinately as well as copying the signal you also copy the noise and you just end up where you started from.

Signal is constant but noise is random, stacking allows combining of the signal which is constant but averaging the noise which is random thereby increasing the signal to noise ratio (I'm sure others can provide a much more scientific answer to the question) which is why multiples of the original do not increase the SNR.

Brendan

[Psychobilly]

Yep that's the long and short of it... you could just mathematically multiply the data rather than adding "copies"...

Billy...

[roundycat]

I think it is down to uncertainty (noise) being the square root of the signal if you consider shot noise and for the purpose of the argument ignore other types of noise that creep in. So, if the noise does not increase as quickly as the signal then longer exposures or stacking multiple frames leads to a bigger 'gap' between the signal and the noise. The signal is more or less constant so re-inforces, the noise is random so cancels out.

Dennis