Astrophotography Image Processing with Graxpert, Siril & GIMP
Second Edition (version 2.0)
22nd July 2025: This guide is currently unavailable. It is being revised to reflect the changes in the newly released version 1.4.
Installation
The links below help you install the software you need:
Siril: https://siril.org/download/
Starnet: https://www.starnetastro.com/download/
Graxpert: Latest versions including pre-release https://github.com/Steffenhir/GraXpert/releases
GIMP: https://www.gimp.org/downloads/
The Guide
The book offers clear, step-by-step instructions to help you transform RAW and FITS images of astronomical objects into stunning final images. With a focus on clarity and accessibility, it breaks down the core processes to ensure that even beginners can follow along with ease.
In addition to traditional One-Shot Colour (OSC) cameras, including both dedicated astrophotography cameras and DSLRs, the guide also covers the use of smart telescopes like the ZWO Seestar, making it an essential resource for a wide range of astrophotography enthusiasts.
Support Free Software Development
If you use this software and would like to support it’s continuing development please donate here, I do.
https://siril.org/donate/
https://www.gimp.org/donating/
GraXpert does not currently have a donation page.
Downloads
The guide uses images of M31, the Andromeda Galaxy, as a worked example. Here’s how to get the files so you can follow along. Click the link below to download the zip file:
containing the following two items :
1) The Folder M31And, which contains samples of the original image files:
A small sample of the original image files that have been “binned” to reduce their size. The original LIGHTS, DARKS and FLATS amount to over 30GBs. This is a subset consisting of:
- 10 Lights
- 5 Flats
- 5 Dark Flats (in the biases subfolder)
- 5 Darks
You can use this to practise using the Siril “Stacking” Script, “Osc_Preprocessing” All these files are in their correct subfolders. Just make “M31And” the Home folder and run the script. The stacked image you produce will be based on just 10 Lights of lower quality than the stacked version used in the examples, which is based on 292 Lights. DO NOT use the image you get in the subsequent processes; instead, use:
2) The full stacked image “M31.fit”
The full stacked image, waiting to be processed. Unstretched, so you will need to turn on the “View Only Stretch” to see it.
M31Final.Jpeg : As the name suggests, this is the version after all processing stages, as described in the guide. This file is shown below so you can see what can be achieved using these free software systems. (Right Click to Download)
