Astro image processing demo : A beginner-friendly workflow with Siril, GraXpert & Affinity.

Following our Astro Image Collection Challenge held in November, here's our image processing demo. The image we’re going to build comes from a dataset kindly provided by Vaonis community member Frédéric Courteix. He captured the Elephant’s Trunk Nebula (IC 1396) with a Vespera 2 smart telescope over several nights, then exported a pre-stacked 16-bit TIFF from the Singularity.

In this guide, we’ll walk through a complete processing workflow based on that dataset:

Siril – clean the background and calibrate colors

GraXpert – refine background and reduce noise

Affinity – stretching, color, contrast, and final polish

StarXTerminator (plugin) – separate stars from the nebula

The explanations are aimed at beginners and intermediate users. You don’t need to be an expert to follow along; just some basic familiarity with opening files and working with layers is enough.

Here's the video and transcript.

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1Dataset & tools 2First contact in Siril 3Background in Siril 4Astrometry & colors 5Export linear FITS 6Stretch & star separation 7Curves on the nebula 8GraXpert background & noise 9Final polish in Affinity 10The background isn’t black 11Export & recap

1. The Dataset & the Tools

The data:

Object: Elephant’s Trunk Nebula (IC 1396)

Telescope: Vaonis Vespera smart telescope

Integration: ~21 hours over 8 nights

Mode: Mosaic to frame the whole nebula

Environment: Suburban sky, sometimes with the Moon up

File: Pre-stacked 16-bit TIFF exported from the Vaonis app

Why start from the TIFF and not a JPEG? Because the TIFF is:

Linear (no edit applied yet)

16-bit, preserving faint details and subtle nuances

Much better for serious processing than an 8-bit compressed JPEG

Software we’ll use:

Siril – free, cross-platform astro processing tool

GraXpert – free tool specialized in background extraction and noise reduction

Affinity Photo – paid but affordable; powerful layer-based editor

StarXTerminator – paid plugin for star removal (optional but very useful)

2. First Contact with the Image in Siril

2.1. Open the linear stack

Launch Siril.

Open the 16-bit TIFF from Vespera.

At first it will look almost completely black. That’s normal:

The data is linear, meaning it hasn’t been brightened yet.

All the nebula signal is stuck in the darkest part of the histogram.

2.2. Use the visual stretch (for your eyes only)

At the bottom of the Siril window:

Choose a display transformation (AutoStretch).

Important: this doesn’t…