Copyright © 2012-2023, Team free-astro <https://free-astro.org/index.php/Siril> <https://www.siril.org>

Siril is an astronomical image processing tool.

It is specially tailored for noise reduction and improving the signal/noise ratio of an image from multiple captures, as required in astronomy. Siril can align automatically or manually, stack and enhance pictures from various file formats, even image sequence files (films and SER files). It works well with limited system resources, like in embedded platforms, but is also very fast when run on more powerful computers.

Contributors are welcome. Programming language is C, with parts in C++. Main development is done with most recent versions of libraries.

For compilation, these tools are needed in addition to the base development packages:

• meson
• ninja
• cmake

Then, mandatory build dependencies:

• glib-2.0 (>= 2.56.0) Glib Convenience Library
• GTK+ 3, (>= 3.20) as GUI toolkit
• lcms2 for color space management
• cfitsio for FITS image read and write
• wcslib (>=7.12) to handle astrometric data
• fftw3 for Fourier transforms
• GSL (The GNU Scientific Library) for PSF implementation, histograms and background extraction
• A C++ compiler for opencv code and avi exporter
• libopencv for various image transformation algorithms (>= 4.4, 4.2 is possible without some shift-only registration)
• json-glib-1.0, (>= 1.2.6) for Siril update check, spectrophotometry color calibration and metadata output

Siril works internally with FITS files, but other file formats can be used as input and converted using the conversion tab of the control window. Some file formats are handled internally, like BMP, PPM and SER, some require external libraries listed below. Libraries need to be present at compilation time, or their support won't be included.

• libcurl for web access
• exiv2 to get thumbnails from files
• libraw for DSLR RAW files import
• libffms2 for films import (any format supported by ffmpeg)
• libtiff (>= 4) for TIFF format support
• libXISF (>=0.2.7) and zstd for XISF format support
• libjpeg or compatible libraries like libjpeg-turbo for JPEG format support
• libjxl for JPEG XL format support
• libheif for HEIF format files import
• libpng (>= 1.6) for PNG format support
• libavformat, libavutil (>= 55.20), libavcodec, libswscale and libswresample for avi export (usually provided by ffmpeg)
• libgit2 for git integration to sync with the official siril-scripts repository
• criterion for unit testing with meson (development)

All these libraries and programs are available in most Linux distributions and free systems, maybe with the exception of ffms2 that is not as popular as the others and may need to be compiled.

Siril accepts commands from the graphical command line, from scripts as a file that contains a sequence of commands, or from a named pipe. The list of supported commands is documented here. We recommend to use the siril-cli binary for that as no X-server is needed.

Some general purpose scripts have been made by the developers and some power users, and are provided with the source code and some installers. When they are in some default directories or in the directories defined by the user in the settings, scripts appear in a top-menu of the main window. See this page for more information about scripts and a list of scripts ready for use.

The named pipe is only enabled when using Siril in a non-graphical mode and when the -p argument is passed to the program on the command line.

We maintain binary packages of the latest stable version of Siril. A full list of all releases is available on free-astro as well as Siril's website. The available packages per relesae might differ.

• Ubuntu and Linux Mint: ppa:lock042/siril
• Windows: see Downloads
• macOS: see Downloads

You can get Siril's source code from the release archives on the webpage or fetch the latest version from our repository on GitLab:

git clone --recurse-submodules https://gitlab.com/free-astro/siril.git

Siril uses the Meson build system. Run the following commands:

# adjust the prefix to wherever you want to install Siril
meson setup --prefix /usr/local --buildtype release _build
ninja -C _build
ninja -C _build install

To update your build/installation, run the following commands:

git pull
git submodule update
ninja -C _build install

To uninstall Siril, run the following command:

ninja -C _build uninstall

Using meson to build siril requires all optional dependencies to be available or explicitly disabled on the meson command line adding -Dexiv2=false for example. The autotools way still only enables dependencies that are found and is available using autogen.sh.

The official JHBuild-based build scripts are available in the siril_macos repository.

Alternatively, you can install Siril via Homebrew. Please note that this is not maintained by Siril developers.

brew install siril

The build process using msys2 is documented here.

If you're interested in contributing to the translation of the application and documentation, we encourage you to use Weblate. Weblate is a powerful web-based translation tool that allows for easy collaboration and efficient translation workflow.

Flexible Image Transport System (FITS) is an open standard defining a digital file format useful for storage, transmission and processing of scientific and other images. FITS is the most commonly used digital file format in astronomy.

Since FITS is a container and doesn't specify the order and size of data, it's useful to fix it at some point. Currently, Siril uses 32-bit floating point per channel values (TFLOAT), and images are stored channel after channel on a bottom-to-top, left-to-right order. The convention chosen is the same as professional tools, like ds9 (Harvard Smithsonian Center for Astrophysics) and fv (FITS viewer from NASA) that store images bottom-up too. More details are described here.

All files imported and converted in Siril or files exported by Siril are in this FITS format, except sequence files like SER and films, which are read from the file and converted on-the-fly. Films should be converted to SER now to process them, many parallel operations are unsupported on them.

Siril makes a strong case for the use SER sequences against the generic film containers that are not well suited for astronomy data and that may not be read the same way by different players. Siril can convert any film format supported by FFMS2 (probably all ffmpeg formats, which is a lot) to SER, and even any image sequence to SER.

Siril supports SER v3. See this page for more details.

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GPL-3.0-or-later