A leap forward for open-source software
Released on December 5, 2025, Siril version 1.4.0 was followed by two quick patches (1.4.1 in January and 1.4.2 in February 2026). Together, they constitute the most ambitious update since the interface overhaul in version 1.0.
For those new to it, Siril is the go-to free software for stacking and processing astronomical images. It is available on Windows, macOS, and Linux, and it is entirely open-source.
Python scripts: Siril becomes extensible
This is arguably the most significant change. Siril 1.4 integrates a full Python scripting engine, with access to nearly all of the software's internal functions. In practice, this means that any developer, or motivated enthusiast, can write a module that integrates natively into Siril.
Even better: an automatic download system from a Git repository lets you retrieve community scripts in one click. It is thanks to this system that tools like VeraLux or Syqon Starless Zenith (which we discuss in other articles) are now accessible directly from Siril.
Why this matters for you
If you are a beginner, Python scripts give you access to advanced features without leaving Siril. No more juggling between three different programs: the ecosystem grows from within.
Drizzle: more detail in your images
Drizzle is a technique invented for the Hubble Space Telescope. The principle: by combining images that are slightly offset from each other (which happens naturally during tracking), you can reconstruct a resolution higher than that of the sensor.
Siril 1.4 implements this technique natively. With a sufficient number of exposures (typically 50+), you can gain sharpness on small structures: spiral arms of galaxies, nebula filaments, planetary details.
In practice
Drizzle is configured in the stacking settings. You choose a factor (x2 is the most common) and Siril handles the rest. Note: processing time and file sizes increase significantly.
Spectrophotometric Color Calibration (SPCC)
SpectroPhotometric Color Calibration uses data from the Gaia catalog to calibrate the colors of your image based on the stars identified in the field. The result: colors faithful to the physical reality of the photographed objects, without having to guess white balance settings.
This function now includes atmospheric modeling that corrects for extinction due to air mass, an asset for those who photograph at low altitude.
Offline Gaia catalog
Good news for evenings without an internet connection: Siril 1.4 supports a local Gaia catalog, indexed in HEALpixel format. A few gigabytes to download once, and you are self-sufficient in the field.
ICC color management
Siril finally adopts a complete workflow based on ICC profiles. Is your monitor calibrated with a probe? Siril takes it into account from the beginning to the end of processing. No more surprises when exporting to JPEG: what you see on screen is what you get.
Transformation curves
A new curves tool makes its appearance, similar to what you find in Photoshop or Darktable. It allows you to finely adjust contrast, brightness, and saturation channel by channel, directly within Siril.
Combined with the ability to work on a region of interest (ROI), you can now refine the processing of a specific area without affecting the rest of the image.
Mosaics and astrometric alignment
Siril 1.4 handles astrometric alignment for assembling mosaics, even when images have little overlap. Fusion masks with normalization ensure smooth transitions between tiles.
For owners of a Seestar S50 or any smart telescope with a relatively narrow field of view, this is excellent news: assembling a panorama of the Milky Way or covering an extended object becomes much simpler.
Performance and usability improvements
A few welcome daily improvements:
- GHT (Generalized Hyperbolic Stretch) 2x faster thanks to code refactoring
- JSON parsing 10x faster (useful for catalogs)
- Reduced memory consumption when processing sequences
- JPEG XL format support for import and export
- FITS keyword management directly from the interface
Summary
Siril 1.4 transforms an excellent stacking software into a complete processing suite. The addition of Python scripts opens the door to a growing plugin ecosystem, and the new features (drizzle, SPCC, curves, ICC) significantly close the gap with paid solutions like PixInsight.
If you have not updated yet, now is the time. And if you have never tried Siril... there is no longer any excuse not to start.
Download Siril 1.4: siril.org