Please review my image at https://astrob.in/n4jhe2/0/
The image is taken with Baader SHO narrowband filters. 40 hours in total exposure time. 120mm aperture, F/5.3.
I tried everything to remove the small but noticeable “blemish” or artifacts in the background where SNR is low. And I tried not to sharpen low SNR areas. These seem to come along with raw files and become noticeable after BlurXT, StarXT and NoiseXT.
So the question is how to smooth out background?
Thank you.
It looks like sharpening artifacts to me. You say you didn’t sharpen those areas but it sounds like you did use BlurX.
I agree with Tony. You mention that they become noticeable after using those tools. These tools should always be used with care, the default values are usually way to much deconvolution. If there are any issues in the raw data they will become a lot more prominent too, as the software may interpret it as features. Examples of such issues are star residues if blurx is used to “cure” misshaped stars.
Try dialing back a bit on those processes, and perhaps share some previews of auto-stretched masters on those areas.
This looks like walking noise that got fried in processing.
Did you dither?
How long were your subs?
In what order did you use blurx, noisex, and starx?
Showing raw data would also help.
Artifact. But also please crop it slightly tighter. There’s artifact all along the top (and to a smaller extent the bottom) you can crop out, and then there are two bright stars along the bottom that should be cropped out. By cropping it slightly tighter you lose hardly anything in the image in terms detail or but it will significantly improve it. It’s not much, I’ll link a photo showing all it needs. 📷 Screenshot 2025-08-26 at 17-39-06 NGC 6888 and WR 134 - AstroBin.png
Its hard to say anything except that it is indeed full of artifacts and squiggles. Could you post an example image from an earlier stage of the process? Such as after gradient removal and colour calibration (or in this case a crude colour workflow to get the palette you are looking for). Just with an autostretch applied, before stretching or the RC-Astro tools.
Those background squiggles look a little bit like NoiseXT AI3 artefacts, but this is way more extreme than i have seen with my data so not sure where to point. My guess is you have overcooked the image with too aggressive application of StarXT, BXT, NXT, and perhaps in the wrong order.
Do share a simpler processing example though, will help in troubleshooting.
📷 BlurXT_Correction_Only.png
This is the low SNR area processed by BlurXT correction only, following by NoiseXT and StarXT to show the artifacts.
📷 BlurXT_sharpen_stars_zero_sharpen_nonstellar_zero.png
Added BlurXT with all parameters dialled down to 0, following by NoiseXT and StarXT to show the artifacts.
📷 HT_Stretched_Only.png
Not processed at all. HT stretched only.
FYI: Dithering every sub-exposure. SHO combined. 6 hours each channel. 10 minute sub.
Bo Chen · Aug 26, 2025, 11:03 PM
📷 HT_Stretched_Only.png
FYI: Dithering every sub-exposure. SHO combined. 6 hours each channel. 10 minute sub.
This does not look like it has not been processed. It’s pretty clearly SCNRed. Looks like it has been denoised and/or blurxed too.
Attached are previews of master files.
Question is where the artifacts come from? Is it the data issue?
Thanks
It looks very weird. What software did you use to stack? Did you drizzle?
Yes drizzled in NINA
Processed in Pixinsight. WBPP, then NormalizeScaleGradient, then DrizzleIntegration.
After seeing the raw data I’m even more confused. It looks very much processed, the worm-looking stars remind me of blurx artifacts. The Oiii and Sii stacks have some very clear walking noise. I think you should double-check if you had the dither command in your sequence in NINA or blink your exposures and see if they were dithered. If they were, I think it’s probably a calibration issue.
What camera did you use? Which calibration frames did you use?
Oh, i mixed up the files. These are processed by blurXT correction only. Nothing else is done. these are blurXT artifacts, aren’t they?
Question: how to get rid of walking noise and worm like artifacts?
Bo Chen:
Oh, i mixed up the files. These are processed by blurXT correction only. Nothing else is done. these are blurXT artifacts, aren’t they?
Question: how to get rid of walking noise and worm like artifacts?
BXT correct only should be the first process before running color calibration, as it can actually help SPCC get better results. Deconvolution should only be done after SPCC. I personally won’t touch any noise reduction before I’m almost done with an image.
To OP: You need to show us what the raw data with a simple auto-stretch looks like. Which means absolutely no processing done to it. Load your master file in PI > activate STF and take a screenshot. I’m guessing your stars look terrible in these areas, which is why you get a lot of those weird holes where the program is trying to reshape your stars. BXT correct only is not magic. It can work well with slightly misshaped stars, but if the stars are bad - the result will be bad too. Stretching the stars less than the background will only further enhance these issues because their original shape has left holes all over the place. Also, if your stars are bad, everything else in those areas will be sub-par as well. So the main issue would probably be to fix whatever is causing this, which could be a number of things - hence, we need to see raw data.
TLDR; grab some screenshots from a STF preview of your untouched master (No BXT or anything else).
EDIT: TBH the published images look exactly like what poor denoise software can do to an image with all the squiggly artefacts. Typically Topaz, Imagenomic etc. You could probably, like others point out, get the same if you adjust the settings in NXT in a weird way. I have personally not seen this happen with NXT though.
📷 HA_Preview01.tif
thanks!
Chris White- Overcast Observatory · Aug 27, 2025 at 11:24 AM
Are you running bxt on starless images?
No.
What camera did you use for this image and which calibration frames did you use? If the raw stack looks like that it's most likely a calibration issue
Mikolaj Wadowski · Aug 27, 2025 at 01:56 PM
What camera did you use for this image and which calibration frames did you use? If the raw stack looks like that it's most likely a calibration issue
Seems to be a night of bad focus or seeing that led to patterned noise in background and slightly out of focus stars. Re-running WBPP after taking those subs out. Will be able to tell if this is the true cause.
Thank you.