What processing steps can Siril perform on astronomical images?

Updated

Siril covers a full astro-imaging workflow in one application: calibration, registration, stacking, enhancement, and scientific analysis. It can run these steps automatically through dedicated scripts or manually if you want control over each stage. The current release listed on the site is version 1.4.4 (June 17, 2026), available for Linux, Windows, and macOS.

Calibration

The first preprocessing step removes unwanted signal and pattern from RAW images. Siril works with master calibration files:

  • Bias frames
  • Dark frames
  • Flat frames

This is the stage where sensor artifacts and fixed-pattern noise are addressed before any alignment or combination happens.

Registration and stacking

Stacking improves the signal-to-noise ratio by combining many registered individual images. Two things matter here:

  1. Registration aligns the frames first. Siril lets you adapt the registration method to the case — on all stars, on a single star, or on the nebulae body — which makes alignment nearly never fail even when stars are faint.
  2. Stacking then combines them, and outlier rejection reduces noise further.

For deep-sky lucky imaging, Siril can natively process SER videos and uses all CPU cores, so processing more than 60,000 frames is feasible. Using the SER format or FITS-Cube, only one additional file is created per preprocessing step, and each stacking method runs in parallel.

Enhancement

After stacking, the combined image can be improved before publication. The site lists these operations:

  • Calibrating the colours
  • Applying deconvolution
  • Stretching the histogram
  • And more

Scientific analysis

Because images can contain valuable scientific data, Siril also provides:

  • Tools to analyze star brightness variation (useful for variable-star work)
  • A powerful astrometry interaction that quickly gives you information about objects in the image

How to run these steps

Siril supports two modes, and the choice depends on how much control you want:

Mode Best for Trade-off
Dedicated scripts Reproducible, repeatable processing Less control over each step
Manual processing Keeping control over every stage More decisions and time per image

A practical approach is to start with a script to get a baseline result, then redo individual stages manually once you know which step needs adjustment.

What to check before committing

  • Confirm your camera's RAW format and calibration frames (bias/dark/flat) are supported by your version.
  • If you shoot video for lucky imaging, verify your capture is in SER format or convertible to FITS-Cube.
  • Check the release notes for your platform, since the site notes known issues with version 1.4.4 and marks some Windows builds (MINGW64) as deprecated.

If your workflow is calibration → registration → stacking → colour/deconvolution/stretch → measurement, Siril covers all of it in a single tool.