Syqon StarLess vs PI StarXterminator first impressions comparison

Russell Croman Astrophotography StarXTerminator Processing Advanced Review
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Georg N. Nyman avatar
Georg N. Nyman avatar

Syqon StarLess vs PI StarXterminator - first impressions:

I downloaded the current most recent version of the “new kid on the block” - Syqon.it .

Syqon launched some new software for image processing, among them “StarLess”.

It is a quite interesting software, works very fine on some images, but fails like SXT on some others.

Here some results - first an easy one, the famous Xmastree Nebula. I used an image which contains not too many stars and consists mainly of the nebula in Ha,OIII and SII. StarLess works fine, but if you look very close, the details of the starless image are slightly less well defined as those from SXT. Both results are imo fine and acceptable.


📷 PI_SXT.jpgPI_SXT.jpg
📷 StarlessSyqon.jpgStarlessSyqon.jpg📷 Original.jpgOriginal.jpgA detail showing that the fine details in the StarLess image are slightly less well defined compared to those from the SXT image:

📷 Syqon_vs_PISXT.jpgSyqon_vs_PISXT.jpg

Now to a difficult image, NGC1737 - it contains tons of small stars and both programs are unable to remove all of them. No wonder, some of those tiny stars are neither bright nor well differenciated from the background. In the linear mode, SXT was able to remove all of them, but here in this case, in the stretched mode, both failed on some of them.
But what is much more a problem is the fact, that StarLess removes quite a large part of the nebulae as well - those which are rather dim and not too much contrasted. That is not good at all. I pointed this out to the developer already during the beta preview some time ago, he told me, that that problem got fixed but obviously not.
Yes, I am aware, this image is a pain in the neck for star removal plus leaving the rather dim nebulae untouched, but PI´s SXT can do it, as one can see - at least the nebulae remain OK.

📷 PI_SXT_NGC1737.jpgPI_SXT_NGC1737.jpg

📷 StarlessSyqon_NGC1737.jpgStarlessSyqon_NGC1737.jpg📷 OriginalNGC1737.jpgOriginalNGC1737.jpgHere some detail regarding the destruction of nebulae by StarLess - compared to SXT

📷 SyqonNGC1737_vs_PISXTNGC1737_Detail3.jpgSyqonNGC1737_vs_PISXTNGC1737_Detail3.jpg📷 SyqonNGC1737_vs_PISXTNGC1737_Detail1.jpgSyqonNGC1737_vs_PISXTNGC1737_Detail1.jpgHave you made already some experiences with that new software - what is your impression?

Would be interesting to hear from you!

CS
Georg

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Willem Jan Drijfhout avatar
Willem Jan Drijfhout avatar
Thank you for this direct comparison. After some other mentions of this tool, this comparison was exactly what I was looking for. So your findings suggest that the performance ranges from much worse to almost as good as SXT. 
In some of the videos on this topic where the tool is shown in Siril and SAS, there appears to be noise reduction going on as well, especially in the background areas. Is that something you have noticed as well?
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Georg N. Nyman avatar
Georg N. Nyman avatar

Willem Jan Drijfhout · Feb 11, 2026, 11:15 AM

Thank you for this direct comparison. After some other mentions of this tool, this comparison was exactly what I was looking for. So your findings suggest that the performance ranges from much worse to almost as good as SXT. 
In some of the videos on this topic where the tool is shown in Siril and SAS, there appears to be noise reduction going on as well, especially in the background areas. Is that something you have noticed as well?

Yes, I agree - I have written a short review of Syqon inside SASpro on my website - sorry it is in German: https://www.nyman.at/sternentfernung-make-it-starless.html

My impression is, that Syqon starless is slowly but steadily getting better - I was working with it in the very beginning, but at that time is was not impressive. Now, I must say, with certain targets, it is a real competitor to SXT.
But I also must say - none of the star removal programs are perfect - no surpise as nothing is perfect :-)

Noise reduction - well, my actual impression is, that that function is best with NXT in PI. The one on SASpro is OK, but I am not impressed by it. The noise reduction due to star removal is basically due to the replacement of the removed star by information gathered from its nearest vicinity.

CS
Georg

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Willem Jan Drijfhout avatar
Willem Jan Drijfhout avatar
Thank you Georg. 
Regarding the noise reduction, this makes sense. But like you say, rather than it being a by-product of another process, better to just focus on noise reduction in isolation and NXT works exceptionally well.

CS, Willem Jan.

Btw, nice website, also liked your photos on crystals.
andrea tasselli avatar
andrea tasselli avatar
Willem Jan Drijfhout:
NXT works exceptionally well


No, not really...
Aloke Palsikar avatar
Aloke Palsikar avatar

My results from SyQon on Siril were very good as well. The artefacts from Star removal are much better as compared to StarNet++ Does some amount of denoising as well which makes the image and nebulosity much clear.

Yet to try on multiple images but sofar results look promising

Good effort from Zenith for Siril users

Georg N. Nyman avatar
Georg N. Nyman avatar

andrea tasselli · Feb 11, 2026, 01:48 PM

Willem Jan Drijfhout:
NXT works exceptionally well



No, not really...

NXT is OK, but imo not really excellent - from what I found out is that you have to be very careful regarding the amount of reduction because it creates artefacts and artificial structures quite easily. From what I tried is that noise reduction results are better when I applied a subtle reduction twice than one only with a larger amount set. Maybe this makes sense…. I am sure, Andrea has an opinion on this as well!