A good idea or not - Stacking the Same good Exposure

[netwolf]

Hi All.


How about stacking the same good Exposure? What is the diffrence between doing this and stacking multiple exposures of the same thing. I understand that atmospherics can affect exposures and some will be better than others, but what if you ranked them and took the very best and just stacked them multuple times.

Is there any new "data" in the Second or Third exposure that is not there in the first if exposure time has not changed.

Just wondering if anyone has attempted this and what the results are like.

Regards
Fahim

[Terry B]

Essentially no improvement. You could just multiply the image by 2 with the same effect.
Adding multiple exposures increases the S/N ratio because the noise is random but the image isn't. Adding the same exposure will increase the noise as well as the signal.

[peter_4059 (Peter)]

I think the point of stacking is to average out the (randomly distributed) noise. Ie the noise in one frame is in a different location in the next whereas the image is always in the same position so taking an average re-inforces the signal and reduces the noise level. If you stack the same image the noise will be in the same position in all the frames so will not average out.

[netwolf]

Ok I understand that. thanks

[leon]

If you stack the same one image it will always be the same, one plus nothing else is still one.

leon

[spearo (Frank)]

Fahim,
everyone's comments are correct, for the record I tried this quite some time ago thinking exactly as you suggest, and of course it made no improvement since there is nothing to "even out".
its by trying and asking that we all learn
cheers
frank

[netwolf]

Its interesting that random noise is the reason for duplication. And this concept does ring bells for me from my uni days studying signal processing. I just thought perhaps that if maybe you could filter out the noise and create a second artifical exposure and then Add it. Or use a Algorithim to add that does this automatically wheryby it "intelgently" recognisises signal from noise and removes it to create an artifical 2nd, 3rd and fourth exposure. Or perhaps use one Dark frame to get some "data" on the noise and what it "looks" like to then intelgently filter the frame of it.

So if that were possible then the Signal/Noise would be diffrent in the 2nd, and consecutive frames theyrby hopefully bosting the Signal strength over the process. I wonder if similar techniques are not employed in Radio Telescope work to fitler noise and boost signal. And what about something like a software Differential amplifier, that rejects noise and boosts the common signal, but i suppose thats what happpens when you take two frames.
So perhaps 2 good frames would be enough to isolate noise from signal by examining the common signal features that should not be random idealy. Like using those Noise buster headphones.

Sorry for the post in this fashion, i am writing as i think.



Regards
Fahim