Introduction

Helia is a free, open-source stacker for pictures of the Sun. You point a telescope and a camera at the Sun and record a video, a few thousand frames long. Each frame is blurred a little differently by the air above you, because the atmosphere is never still. Helia ranks the frames by sharpness, lines them up (the whole disc, and many small patches of it, because the air bends the image differently across the Sun), and averages the best ones into one sharp picture, written as a 16-bit TIFF, an 8-bit PNG or a FITS file. It knows the common solar filters (H-alpha, calcium K and H, magnesium, sodium, helium D3, H-beta and white light), picks sensible settings for them, and can colour the result for sharing.

This technique is called lucky imaging. It does the job of tools such as AutoStakkert!, in a single program that runs on Linux, Windows and macOS, on x86_64 and ARM, and does its heavy maths on whatever GPU you have.

Helia is written in Rust. It comes as three front ends over the same engine:

• helia-gui, a desktop app that walks you through the steps. See Using the desktop app.
• helia, a command line tool for scripts and batch work. See The command line.
• helia serve, an HTTP and WebSocket API for notebooks and other programs. See The API.

Where to start

• New to Helia? Download and verify, then Installation and First launch.
• Want to see every step? The step-by-step walkthrough goes from a raw capture to a finished picture with a screenshot at each step.
• Have a particular capture? The recipes cover H-alpha, white light, calcium K, phone video, a Bayer grid, batches and scripting.
• Something wrong? Troubleshooting and the FAQ.

Copyright and licence

Copyright (C) 2026 Laurence Horrocks-Barlow. Helia is free software under the GNU General Public License, version 3 or (at your option) any later version, with no warranty, and with the additional terms in ADDITIONAL-TERMS.md that keep the author's name and this dedication with the program; the About page of the desktop app, helia --version and the contributing notes have the details. Helia is made by Laurence Horrocks-Barlow. If you are interested in anything else I make, visit 12hobbies.studio.

Dedication

Helia is dedicated to my daughter, the light of my life. Her middle name is Helia, because she has an energetic spark. She has not stayed still since the day she was born, which suits software whose whole job is catching the sharp moments in something that never stops moving.

Status

Helia is in early development. The stacking pipeline, the command line, the desktop app and the API work today, with sharpening, deconvolution and everyday adjustments, and it applies dark and flat frames and a bad-pixel map before it analyses anything. Drizzle and the other planned features are listed in the Roadmap, and each page of this guide says plainly when something is not available yet. The plan and every decision taken so far are kept in the project's private issue tracker.

Pre-release archives for Linux (x86_64 and aarch64) and Windows x86_64 are available to early-access users (contact 12hobbies.studio); macOS is built from source. See Installation.

Supported platforms and GPUs

Helia runs its heavy maths through wgpu, which talks to whatever graphics API your system has:

With no usable GPU, Helia falls back to a multi-threaded CPU path that gives the same results. GPU acceleration explains how the choice is made and what to do when your GPU is not found.

Optional machine-learning features are planned (they would run through ONNX Runtime on CUDA, ROCm, DirectML, OpenVINO or CoreML, with experimental Coral Edge TPU support). None of that exists yet.

How this book is organised

• The User guide takes you from installing Helia to a finished image, and explains what each setting does.
• The Reference pages list every option. The command line and API references are generated from the code, so they cannot drift from it.
• The Developer guide covers the architecture, how to build and test, and how to contribute.
• The Roadmap lists what is planned, with links to the issues.

Helia is licensed under GPL-3.0-or-later. If it helps your imaging, you can support its development through the links in .github/FUNDING.yml in the repository.

Helia is part of 12hobbies.studio.