Why remove stars?
Star removal has become a common step in astro processing. The idea: separate the nebulosity from the star field to work on each component independently. This way, you can push the contrast and saturation of the nebula without blowing out the stars, then recombine them properly at the end.
Until now, two tools dominated this field: StarNet++ (free, open-source) and StarXTerminator (paid, PixInsight/Photoshop plugin). A third player has entered the scene to shake up the established order: Syqon Starless, developed by SyQon.
How it works
Syqon Starless uses a neural network trained on real astronomical data. Its distinctive feature: it performs a temporary pre-stretch to identify and locate the stars, applies the removal, then mathematically reverses the stretch to return the image to its original linear state.
This mechanism preserves the scientific integrity of the data: your starless image remains linear, ready for the stretch of your choice (VeraLux, GHS, curves...).
Another major advantage: Syqon Starless performs noise reduction in the same pass. The neural network distinguishes the astronomical signal from random and structured noise, and removes the latter at the same time as the stars. Two operations in one.
Three models, three use cases
| Model | Parameters | Platform | Price |
|---|---|---|---|
| Axiom v2 | ~12 million | Standalone (Win/Mac) | Commercial |
| Zenith | ~1-2 million | Siril script | Free |
| Nadir | Compact (derived from Axiom) | SETI Astro Suite plugin | Included |
Axiom: the flagship
The most powerful model, with approximately 12 million parameters. Its representational capacity allows it to handle dense star fields, low signal-to-noise ratio data, and images with pronounced gradients. Available as a standalone application for Windows and macOS (including Apple Silicon).
Zenith: the free entry point
A lighter model, integrated into Siril via the Python script SyQon_starless.py. Since January 2026, it has been available in the official Siril script repository. For Siril users, it is the simplest way to test AI-powered star removal without spending anything.
Nadir: for SETI Astro users
A compact variant of Axiom, designed as a plugin for the SETI Astro Suite. If you already use this ecosystem, Nadir integrates natively.
Comparison with the competition
We tested the three main solutions on an image of M42 (Orion Nebula) and an image of NGC 6188 (Dragons of Ara), both captured with a Seestar S50.
Removal quality
| Criterion | Syqon Starless | StarXTerminator | StarNet++ |
|---|---|---|---|
| Residual artifacts | Rare, subtle | Very rare (the cleanest) | Frequent, require retouching |
| Nebula preservation | Good, may nibble at faint nebulosity | Excellent | Variable |
| Halos | None | None | Occasional |
| Noise handling | Built-in denoising | None | None |
Speed (30 MP image)
| Tool | Time |
|---|---|
| Syqon Starless (Axiom) | < 1 min |
| StarXTerminator | < 1 min |
| StarNet++ | 3-11 min |
Price
| Tool | Cost |
|---|---|
| Syqon Starless Zenith (Siril) | Free |
| Syqon Starless Axiom (standalone) | Commercial |
| StarXTerminator | $59.95 (PI or PS plugin) |
| StarNet++ | Free |
Points to keep in mind
Faint nebulosity: Syqon Starless can sometimes confuse very faint nebulosity with noise and partially remove it. On bright, extended objects (M42, NGC 7000), no problem. On IFN (galactic cirrus) or very faint extensions, check the result.
Supported formats: FITS and TIFF 16/32-bit. No JPEG; if you are processing in JPEG, you have other issues to address first.
Star mask export: Syqon exports the star mask separately, which is essential if you use StarComposer (VeraLux) for recombination.
Our verdict
Syqon Starless establishes itself as a credible and modern alternative in the star removal ecosystem. The Zenith model, free and integrated into Siril, makes it an obvious choice for anyone processing with Siril. The built-in denoising is a real plus that simplifies the workflow.
StarXTerminator remains the reference in terms of absolute removal cleanliness, but it is paid and limited to PixInsight/Photoshop. StarNet++, although free, shows its age against the new generation.
If you use Siril, install Zenith and test it on your next image. You will probably be surprised.
Official website: syqon.it/starless