Controlling star size

[almcl]

Need some help controlling stars.

Of late, I find I can stretch for nice, tight stars, not too much bloat, good colour etc, but this gives almost no nebulosity. Here's an example:

stretch for the stars 3.jpg (159.38 KiB) Viewed 3859 times

or I can stretch to bring out lots of nebulosity but the stars end up looking like beached jellyfish and none of the tools (SVDecon, Shrink, Superstructure &c) seem able to help much with this:

stretch for nebulosity 3.jpg (248.7 KiB) Viewed 3859 times

From what I see and read elsewhere this isn't a problem that's unique to Star Tools, which may explain the profusion of star removal tools available either as standalones or incorporated into post processing software.

Has anyone got a workflow that can remove or otherwise protect the stars that would get blown out (as these have been) and allow them to be dropped back in later?

I know how to use the Heal module to remove stars but the background that this leaves still has excess star glow:

Excess star glow.jpg (120.88 KiB) Viewed 3859 times

Some sort of compromise between the two extremes shown above would be great, if anyone has any suggestions?

[hixx]

Hi, please check the Inofficial Manual (download section), Special techniques chapter, page 43-44 "creating a starless image" and "using the Heal module to process stars independently". You can process the starless image separately and add the stars in Layer module later on. You can also run Shrink multiple times on different selections of stars, targeting fat stars stronger and/or use super Structure to push back the star field. Usually there is not a silver bullet which fits all needs, but a combination of multiple effect in slight doses will do the job. hope this helps
clear skies,
jochen

[Mike in Rancho]

The Northern Lagoon? I picked up some of that recently, though it was just a little side-show to the Bubble, M52, and Nova Cas 2021.

Pic 1 seems way understretched to me. I guess that keeps the stars "tight" in a way. I don't know if it's a good way, but I can see that being subjective. But particularly telling are some of the red stars, that in the subsequent version have a proper core and colored surround, in the not-so-stretched version are just tiny red dots.

Pic 2 strikes me as overstretched for the data, though the N Lagoon has detail there.

Maybe somewhere in the middle would work? Stars do make halos by nature of the optical acquisition (and probably PSF's and other fancy stuff that Ivo understands. ) I've never really followed down the starless or remove-and-replace path. And of course the more stretched and bigger they become, the more any usage of heal would have to fill in more interpolated detail.

Were the larger stars included in any ROI you used in AutoDev? I have noticed that with some targets, in particular the West Veil, that 52Cyg has to be within the ROI otherwise it'll bloat pretty good.

Another possibility, starting with a more modest stretch, would be to follow any DimSmall SS with a Brighten SS, the combo should push back some of your stars and halos and then augment the super structures yet again.

The N Lagoon can get exceedingly bright though, as you've probably noticed.

[almcl]

Thank you both for the suggestions.

I found re-reading the Unofficial guide very helpful, Jochen, many thanks!

And Mike's insights were spot on, both examples were 'exaggerated for clarity' as you pointed out.

Using the Heal module (again) I was able to get a slightly better starless nebula and then add the stars back. Still not right, but better than before (I did cheat slightly and used Photo-Paint's layer function to contain the burnt out centre).

NGC 7538 layered.jpg (223.69 KiB) Viewed 3813 times

Now to sort out the granularity in the nebulosity...

[5SmallHokies]

Thank you to all for asking the same questions and directing me to the unofficial guide.

My question is WHEN to perform the Heal module in the 'standard' workflow to remove the stars? Is it after Bin/Crop/Wipe or in between some other set of modules. Logically I have tried it after Wipe and used that also to create the stars only image.

Also, any other tips for removing some of the artifact halos that seem to be left behind? This is particularly true of brighter stars removed. They tend to leave a green/blue hole in the starless image.

Aaron

[hixx]

Hi, I would say, process up to Decon, because this willl give you the real star sizes to start with...
jochen