Quality of Zwo AsiAir plus stacking vs. Laptop Classics DSS / Autostackert+Registax

I was wondering the same thing. So I also want to know a bit more!

Great insight, Dave - thank you!

I agree that the post processing is where the real magic happens.
I am just not confident enough yet, whether its the input stacked image or what I do with it - thats what I asked

Suspicion is, that its my end that can further improve (as not every session delivers the same result on the same matrial)
- so good to know the stacking outputs are similar :-)

Hi Arnie,
Thanks for your post - I'm very pleased to see another ASIAir owner getting great results

I've used the ASIAIR live stacking a few times, and it works very well. The main benefit is that it visualises the image capture process, so you can see your target 'emerge' from the background noise during the course of an imaging session.

The main downside is that you have no control at all over the stacking process, which is entirely non-selective.

When stacking using other applications such as SiriL or DSS (personally I use Affinity which is powerful and very easy to use), you can select individual frames based on image quality, making it easy to reject poor images such as those containing aircraft trails or cloud cover.

Other apps also let you choose the stacking method - mean / median / sigma clipping - which helps enormously when it comes to eliminating artefacts such as satellite trails, without sacrificing what might otherwise be a good image.

So for example, if cloud cover affects 50% of your images in Live Stacking, the cloudy images pollute the stack, and the quality cannot be recovered. On the other hand, if you capture individual frames and stack them later, you can inspect every frame and discard the cloudy ones, and stack only the good ones, yielding a much better result.

Live stacking will never be as good as selective stacking. Of course, ASIAir lets you do both if you select 'keep all frames'.

Just to clarify a few points about stacking ... stacking combines several related but separate processes :-

1. Registration
Registration aligns images, usually by offsetting and/or rotating individual frames, so they all line up exactly.
This helps a lot if your tracking/guiding are a bit out, for example after a meridian flip.

There is no value in stacking frames that aren't well registered.

2. Compensation
If you use compensation frames, this process removes hot/dead pixels, background bias signal and dust.
ASIAir lets you specify compensation frames for this purpose.
Master Frames, like light frames, also need to be stacked, so I find it a bit tedious shifting master frames from a server to the ASIAir.

3. Summation
Essentially, summation inspects each corresponding pixel in each image in the stack, eliminates the outliers, and sums the rest.
The idea here is that summation averages out noise, which is random, and reinforces signal, which is not.

The result is a significant improvement in the signal/noise ratio - this is the main purpose of stacking.

As a side note ...
Signal improves linearly with the number of subs, but noise is reduced according the the square root of the numbers of subs.
So - if you take 25 subs, the S/N is improved by a factor 5, if you take 100, by a factor of 10. There is a diminishing return on the number of subs, ~ 50 being the sweet spot, because of the emergence of read noise with larger numbers, not to mention the extra processing time.

However, as Dave rightly points out - the next stage is where automation ends and creativity begins.

As with many technical endeavours, the thing that usually requires the most work is BCK - between chair and keyboard

Ive never actually tried using the ASIAir to do  a live stack with a target crossing the meridian - but I would have expected it to manage the MF in such a case - I might try it next time

I do know that other apps (eg Affinity) manage this seamlessly and elegantly - after analysing all the images, they simply rotate the post-flip images to match the pre-flip ones.

Hi Arny,
I've never used the DSO stacking feature in ASIAir, but fas as I can tell, it is exactly the same as the live stacking feature.

I encourage you (and everyone on AstyroBin) to try Affinity Photo - here is a link for you.

It has a robust set of Astrophotography stacking tools, as well as a great set of free macros that you can download here, designed by Affinity Experts specifically for astrophotography.

It is also a very powerful image editor - so you can stack your images and process them in one app.

It's more-or-less a direct replacement for Photoshop at a fraction of the price, and you own the license - no annual license fees !

It's cross-platform (Mac, iOS, Windows), and has a 30-day free trial.

Happy to help if you have any questions about it

That's interesting …
You should be able to generate stacks without compensation frames - I've created many stacks on ASIAir without them.

ASIAir can generate compensation frames - which are then stored in folders on the internal SSD or USB stick.

When you do live stacking, you need to tell ASIAir where these files are.
So, you can use any bias/dark/flat frames if you just place them in the corresponding folders, provided they are FITS files and the same resolution as your camera.

Tell ASIAir where these files are located on  your USB stick, or copy them to the internal SSD - which will probably allow the stack to be processed more quickly.

I hope that helps - perhaps you can share more details of your workflow if this doesnt work for you.

Cheers,

Gary

I use Air Plus for polar alignment, focusing, guiding, imaging and downloading data but prefer to do all of my pre-processing (calibration, registration, stacking, etc.) in Pixinsight and all my post-processing in PI and an app called ACD Photo Studio Ultimate.   I shot subs last month of M42 and they were full of satellite streaks.  Pixinsight got rid of them beautifully.   PI has so many more pre-processing options if a sub is problematic in some way that I am taking the time to learn it as best I can.  ASIAIR Plus is ingenious and I love it when I am out imaging, but I think for stacking it's pretty elementary.

Jerry Gerber:
I use Air Plus for polar alignment, focusing, guiding, imaging and downloading data but prefer to do all of my pre-processing (calibration, registration, stacking, etc.) in Pixinsight and all my post-processing in PI and an app called ACD Photo Studio Ultimate.   I shot subs last month of M42 and they were full of satellite streaks.  Pixinsight got rid of them beautifully.   PI has so many more pre-processing options if a sub is problematic in some way that I am taking the time to learn it as best I can.  ASIAIR Plus is ingenious and I love it when I am out imaging, but I think for stacking it's pretty elementary.

I agree, Pixinsight is stunning, yet quite complex, but beautifully logical and very well executed.
Just tutoring myself through to get reliable results of a basic worflow.

Any recommendations for workflows or tutorials to get better at it?