StarTools

I've been reading past posts on stacking and aligning frames for processing in Startools. Ivo has given advice on this in the past and two examples read as follows:

"It is very important to align all channels during stacking. That's because aligning individual frames will always be more precise than aligning just 3 channels after the fact."

"The correct way is to use your stacker to align the two stacks during the stacking stage. To do this stack the one stack (say the RGB stack) as normal, then use this stack as a reference for stacking the Ha frames".

Would it be possible to be signposted to a walkthrough that explains how to "align all channels during stacking" and to "use your stacker to align the two stacks during the stacking stage"? I have used DSS, ASTAP, Siril , Affinity Photo and Astroart for stacking but not come across anything other than options to autoalign specific stacks. My setup use a mono camera with either broadband or narrow band filters. Astroart combines LGRB stacks (GRB then L+GRB) but there is no option I can see that uses a reference stack. DSS registers frames and as part of the process a reference light frame is specified but again there is no option to select a reference stack that I can see.

Consequently, I'm confused by the advice. Is there another stacking software I should be using? Thanks for any help with this!

From what I know, ASTAP is the only one where you can't pick the reference. I don't have APP, and don't stack with Siril, but I believe I have read that the referenced can be chosen.

In DSS, if left to it's own designs, it will choose the best scored light sub as reference. You can override and choose your own reference with a right click and then select from the menu.

And indeed, stacking to the same reference would be preferable to registering the already-finished filter stacks. That said, I use alignment/registration of finished stacks all the time, with either DSS or ASTAP, for various purposes or because my situation doesn't allow subsequent stacking to a previous reference.

Using a finished stack (for example your L) to then stack other filter light subs can sometimes be difficult, because that finished stack has now been converted to 32-bit. It could be done, but some trickery with upping and then reverting the gain may be necessary.

What might be easier is to use the known reference sub from the first stacking job. So, for example, you would use what DSS considered the best-scored sub for luminance, if you stacked that first. To be sure, you could even force-reference that file when stacking L. Then, load in your next set of lights and calibration frames for, say a color filter like R. Then add the L reference file to the lights tab. Right click to make it the reference. Then run registration, but do not stack. After registration completes, uncheck the L sub so that it is not included in the stacking. Make sure that the registration settings have "register previously registered files" turned off, so that it doesn't re-register automatically when you hit stack. Then...stack. Your R files will be stacked to the reference previously chosen. Then do the same for the other filters, using the same L sub as the reference.

One other thing, make sure to stack in standard mode, not intersection, otherwise you will experience much grief trying to composite them all into ST. Cropping all the overlaps will be done after compositing.

Hope that helps -- it should work (I think).

Thanks for replying and the very clear explanation. Will try what you recommend in DSS.

In Siril you would register your first channel and stack as normal. For a subsequent channel you would make a sequence that has, as its first image, either the stacked output from the first channel or the same individual first-channel sub that was the original reference frame. When you stack the later channels you just need to remember to exclude the foreign sub and specify another sub to be the reference image.

In DSS acc. to https://groups.io/g/DeepSkyStacker/mess ... 2C91636152 you simply mark a light as reference and deselect it as to not to be used (in stacking) and proceed as usual…