What Is Siril and What Is It Used For?

Siril is a free astronomical image processing tool for pre-processing and processing astrophotography and scientific images. It is used to calibrate RAW frames, stack many exposures into one image, enhance the result, and analyze scientific data such as star brightness. It fits you if you shoot deep-sky or solar system targets and want either automated scripts or manual control over each step. The current release listed on the site is Siril 1.4.4, dated June 17, 2026.

What Siril does

The site organizes its capabilities into four main areas:

• Calibration — removes unwanted signal and pattern from RAW images. Siril works with BIASES, DARKS, and FLATS master files.
• Stacking — combines many registered individual images to improve signal-to-noise ratio. Outlier rejection reduces noise further.
• Enhancement — improves the stacked image before publication by calibrating colours, applying deconvolution, stretching the histogram, and more.
• Science — analyzes star brightness variation and provides astrometry interaction to identify objects in the image.

Together these form what the site calls a complete astro workflow.

How you work in it

Siril supports two modes:

• Automatic — dedicated scripts run the workflow for you.
• Manual — you keep control over each step.

This matters if you are learning the process (scripts get you a result quickly) or troubleshooting a specific frame (manual steps let you isolate the problem).

Where it performs well

• Deep-sky lucky imaging — Siril processes SER videos natively, which suits this technique.
• Large volumes — algorithms use all CPU cores, so the site states it can process more than 60,000 frames.
• Difficult alignment — registration can follow all stars, one star, or the nebulae body, which the site says makes alignment nearly never fail even with faint stars.
• Efficient storage — using the SER format or FITS-Cube, only one more file is created for each preprocess step, and stacking methods run in parallel.

Downloads and platforms

The download page lists builds for:

Academic use

If you use Siril in published work, the site asks you to cite: C. Richard et al., Journal of Open Source Software, 2024, 9(102), 7242, DOI: 10.21105/joss.07242.

When it may not be the right fit

Siril is built around astronomical image processing, not general photo editing. If your goal is terrestrial photography or non-astronomical image manipulation, its calibration, stacking, and astrometry tools are not aimed at that. If you want a fully guided commercial package with no manual step control, the script-or-manual model here may feel less hand-held.