Speaking from a perspective somewhere below 'amateur' and from someone who also took a first try at the Pinwheel this past Sunday, the background speckling you're seeing may be a result of trying to process the stacked image beyond what the data you collected actually supports. This has been one of my problems for a while ... I want to get as much detail as I can from the image, but the software can't distinguish between DSO data and background, and I tend to over-process the image. If you try to bring the DSO details out too much, you can't help but also bring out the background.
When I took my subs on Sunday, the moon was at about 95% full and was not all that far from the Pinwheel, so I had a lot of background signal. I may be wrong, but I think this is going to wash out some of the detail in your target, and you're just not going to be able to get it back without creating background artifacts like speckling.
By the way, I really like your photo of the Pinwheel. I'm just hoping mine turns out half as good.
Your post is basically an outcry to use masks. If there's one thing I've learned in three years of Astrophotography, then it is to mask. Literally everything.
Sharpening? Mask it!
Noise reduction? Mask it!
Stretching? You bet you'll mask it!
Saturatio? Mask it!
Contrast enhancement? Please, mask it!
Just think about it, do you really want to apply the same adjustments to the brightest part of the image and the darkest? Can there even be a decent outcome? I doubt it...
You'll be surprised how a) easy masks are to make in photoshop and b) clean the result will be. No ugly artifacts, no speckling, nothing. Just smooth details... At least in theory 😁
Edited by Huangdi, 09 April 2020 - 11:22 AM.