AkastroidComparison
Akastroid vs Siril
Siril is free, open source, cross-platform, actively developed and very good. There is no price argument to make here and no capability gap to point at. There is exactly one difference, and it is about who has to know the workflow.
The short answer
Use Siril if budget is the constraint, if you enjoy processing as its own activity, if you want scripting and a command line, or if you already know the sequence of operations and want to control every parameter in it. It is free and it will go further than Akastroid in experienced hands.
Use Akastroid if the sequence is the obstacle rather than the interest - if you have folders of unprocessed frames because you do not yet know what to do with them, or if you also shoot planets and would rather not add three more programs.
Where Siril is genuinely better
It is free, permanently, with no frame cap and no licence to buy. It runs on Linux, which Akastroid does not. It has a scripting language and a command line, so if you process on a schedule or in volume with custom logic, Siril can do things Akastroid has no answer to at all.
It also gives you the whole toolbox. Every operation is exposed with every parameter, and if you know what you are doing you can take an image further than an automatic pipeline will take it. That is a real ceiling difference and it should decide the question for anybody who already has the knowledge.
The actual difference
Both programs run the same workflow. Calibrate, grade, register, integrate, remove the gradient, calibrate the colour, stretch, sharpen. The question is where the knowledge required to run it is stored.
In Siril it is stored in you. Which rejection algorithm, which sigma value, which background extraction degree, how far to stretch, how hard to deconvolve - all of it is asked, and the program will do exactly what you say including when what you say is wrong. That is the correct design for a tool aimed at people who know, and it is an impasse for people who do not.
In Akastroid it is stored in the measurements. Which rejection method suits the stack is a function of frame count and variance. How hard to deconvolve is a function of measured star width and signal-to-noise. Where the black point belongs depends on what fraction of the frame is sky. None of those are matters of taste, so none of them need to be questions. The whole sequence is written out step by step here.
Feature by feature
| Siril | Akastroid | |
|---|---|---|
| Cost | Free and open source | Free to 25 frames a session, then one payment |
| Platforms | Windows, macOS, Linux | macOS now, Windows in test |
| Learning curve | Steep - you drive the sequence | None required - it drives the sequence |
| Parameters | You set them | Measured from your frames |
| Scripting and command line | yes | no |
| Photometric colour calibration | yes, on request | yes, by default |
| Gradient removal | yes | yes |
| Deconvolution | yes | yes, PSF measured from your stars |
| Frame rejection with a named fault | quality metrics, unlabelled | twelve measurements, fault named |
| Planetary and lunar video | not really | yes |
| Explains each decision afterwards | no | yes, with the number behind it |
| Runs entirely offline | yes | yes |
But Siril has scripts
This is the strongest objection to everything above, and it deserves a straight answer rather than being skipped. Siril's OSC preprocessing scripts do automate calibration, registration and stacking, and for a lot of people they are enough.
A script is fixed. It applies the same operations with the same settings to whatever you feed it, because it never looks at the data. A measurement is not fixed. A wide field where 98% of the frame is sky and a close crop of a galaxy where far less of it is need different black points, and a script gives them the same one. A session with forty frames and a session with four hundred want different rejection methods. A night where the seeing collapsed at midnight needs half its frames dropped, and a script will stack them all.
That is the difference between automation and decision, and it is the only claim this page is making.
What Akastroid does not do
No scripting, no command line, no Linux build. Its adjustments are global - no masks and no selective editing. And it is not free beyond 25 frames a session, against a program that is free without limit, which is a real cost and should be weighed as one.
If you have already learnt Siril, the honest recommendation is to keep using it. This page exists for the people who have not, and who have been told that learning it is the price of admission.
Questions
Is Akastroid better than Siril?
Not in capability. Siril goes further in expert hands, it is scriptable, it has a command line, and it is free. The difference is what it asks of you: Siril expects you to know the order of operations and the parameters for each. Akastroid measures your frames and decides them. If you already know Siril, you may well not need this.
Siril has scripts that automate the whole thing. Is that not the same?
It is close, and it is the strongest counter-argument on this page. The difference is that a script is fixed and a measurement is not. An OSC preprocessing script applies the same steps with the same settings to every session you run through it. A wide field of a small nebula and a close crop of a galaxy need different black points, different deconvolution strength and sometimes a different rejection method, and a script cannot tell them apart because it never looks at the data.
Does Akastroid do photometric colour calibration like Siril?
Yes, and it is on by default when your frames record where the telescope was pointing. Akastroid carries a catalogue of half a million stars with measured colours locally, matches your field against it and sets the white balance from what those stars actually are. Siril does this well too, and requires you to plate-solve and invoke it.
Can Siril do planetary work?
Not in the way a dedicated planetary tool does. Siril is a deep sky program; planetary lucky imaging is normally AutoStakkert plus RegiStax plus PIPP. Akastroid handles SER and AVI captures with multi-point alignment, atmospheric dispersion correction and wavelet sharpening in the same application.
Which should a beginner start with?
If your constraint is money and you have the patience to learn, Siril, without hesitation - it is free and it is genuinely good. If your constraint is time and you want a real image from your first session while you work out what any of it means, Akastroid. Both answers are defensible and the free tier costs nothing to test.
Test it against your own Siril result
Free for sessions up to 25 frames. No account, and nothing leaves your computer.