DeepSkyStacker (DSS) vs. Siril: Which Stacking Tool Fits Your RAW Workflow?

If you shoot deep-sky astrophotography on a DSLR or mirrorless camera and don't want to pay $300+ for commercial licenses like PixInsight, two names dominate the community: DeepSkyStacker (DSS) and Siril.

For over fifteen years, DeepSkyStacker was the uncontested rite of passage for every beginner. But over the last few years, Siril has seen rapid development, introducing native 32-bit floating point pipelines, photometric star-color calibration, and automated script execution that rival premium commercial suites.

Which one should you use for your shoots? Let's break down the technical differences.

Head-to-Head Comparison Matrix

1. Calibration Math & Color Calibration

The most striking difference between the two tools is what happens after alignment:

DeepSkyStacker's Approach

DSS is purely a calibration and registration engine. Once it computes your master stack, it gives you a raw 16-bit or 32-bit TIFF file and a basic RGB histogram with three sliders. Most experienced imagers leave the sliders completely untouched in DSS and immediately export the raw result into Photoshop, GIMP, or Siril for actual stretching.

Siril's Approach

Siril is not just a stacker; it is a comprehensive astronomical image processing suite. Its flagship feature is Photometric Color Calibration (PCC):

• Siril plate-solves your image using the coordinates of your target and your focal length.
• It queries the official Gaia or NOMAD star catalogs, analyzes the exact B-V color index of hundreds of cataloged stars in your framing, and calculates a mathematically true white balance.

This eliminates the endless guesswork of trying to manually balance green and blue airglow against faint H-alpha nebulae.

2. File Organization: Where the Workflows Diverge

How each program intakes your camera's SD card is completely different:

DeepSkyStacker: The Multi-Group File List

In DSS, you click "Open picture files", browse to your directory, and select your lights. Then you click "Dark files" and select your darks. If you shot across multiple nights, DSS offers "Main Group" and numbered group tabs at the bottom.

Siril: The Strict Subdirectory Script Pipeline

Siril achieves its speed and repeatability through automated scripts (like OSC_Preprocessing). Instead of asking you to click buttons in a UI, the script expects your working directory to contain four exact folders:

working_directory/
├── lights/
├── darks/
├── flats/
└── biases/

3. Which Tool Should You Choose?

The Unified Workflow: Pre-Sort Once, Use Both

The good news is that you don't actually have to choose one or the other. If you organize your camera card into clean calibration subdirectories (/lights, /darks, /flats, /biases):

1. You can run Siril's 1-click automated scripts with zero risk of script abort errors.
2. You can drag those same organized folders into DeepSkyStacker in two seconds without clicking through individual file ranges.

This is why we built AstroPlot RAW. It reads your raw EXIF metadata in parallel across all CPU cores and plots your shoot on a 2D scatter plot. In under 60 seconds, you can marquee-select your groups, exclude cloudy frames, and export clean calibration subfolders with full 1-click undo safety.