I’ve seen quite a few photos of nebulae on Astrobin where the stars have been completely removed. Some of these are absolutely seamless… you can’t see even a trace of stars, which really brings out the details of the nebula itself.
After processing a session on the Rosette Nebula (NGC 2237), I started looking around for how to do one of those star disappear things all the cool kids are doing. Turns out PixInsight now incorporates a process for that very purpose by Nikita Misiura. But you don’t need PixInsight. It is also available as a stand-alone application for Linux, Mac OS, and Windows. You can download it here.
It is literally a one-step process. You load up your image and apply the process. Stars disappear. Here’s a before of my Rosette Nebula… about 1.5 hours with the HyperStar on a night of good seeing. At f/1.9 with 120 second subs, LOTS of stars in the mix here:
And here’s the same photo with the StarNet++ process applied (and cropped a bit to really focus in on the center of the nebula:
It definitely didn’t get rid of stars completely, as plenty are still visible. But, it eliminated a bunch and really tamped down the brightness of all the others, leaving a pretty good view of the nebula’s structure. This is definitely a PixInsight feature I’ll be playing with in the future.
A tip on using… as of the August 2020 PixInsight update, StarNet++ and its database files are included in the standard installs. But, when you first fire it up, you have to tell it where the database files live. I had thought you’d need to download them from the developer’s GitHub page, but after doing so discovered that they were already installed in the PixInsight library folder (~/PixInsight/Library on Unix systems). So, before trying to download, check your library folder first.