Double Stacking -why not?

[glend (Glen)]

So who has used double stacking to boost data signal levels? By this i mean taking say 30 or more good subs (of the same filter obviously) and after stacking registering and calibrating them to a final stacked image, copying that image and stacking to combine again with the original; or even just making copies of all 30 subs to yield 60 subs prior to processing. This is before any subsequent final processing, stretching, etc. Does this not effectively boost signal levels? Now the assumption is that you have a very low noise camera and good dark calibration has been done. I realise that any residual noise, pattern etc could also be doubled in strength.
Anyone done this? Is it a 'cheat'?

[RB (Andrew)]

Originally Posted by glend

So who has used double stacking to boost data signal levels? By this i mean taking say 30 or more good subs (of the same filter obviously) and after stacking registering and calibrating them to a final stacked image, copying that image and stacking to combine again with the original; or even just making copies of all 30 subs to yield 60 subs prior to processing. This is before any subsequent final processing, stretching, etc. Does this not effectively boost signal levels? Now the assumption is that you have a very low noise camera and good dark calibration has been done. I realise that any residual noise, pattern etc could also be doubled in strength.
Anyone done this? Is it a 'cheat'?

Doesn't yield any benefits Glen.
You're not introducing any new useful signal.
A lot of people have suggested it in the past and much discussion has taken place.
I wish it was that simple but it doesn't work towards a better result unfortunately.

RB

[Atmos (Colin)]

Te reason it will not add anything is because it doesn't add random signal. Your images pre calibration are packed full of random and non random noise. Calibration frames remove the non random stuff eg. bias/dark current. What is left is the random noise.

The idea behind stacking is to get the average signal of what you want and the random noise is decreased by sqrt(n) with n being the number of subs.

What double stacking doesn't do is add any more random noise as it just repeats the random already there.

[glend (Glen)]

Ok i understand, thanks gents.

[DJScotty (Scott)]

Don't worry. I experimented with the exact thing when i first started 4 years ago only to find no effect whatsoever.
Stretched 2 hours of data out to 12 hours with absolutely no improvement in the picture quality.

Scott