Painting with Light You Can't See
A series of imaging workflow documents from my Bortle 9 location
Just beyond my doorstep - LED streetlights, LED floodlights from O’Hare airport, and the orange glow of a city that never fully goes dark. For a long time, I assumed that ruled out serious deep-sky work.
It doesn't.
The right filter changes everything. A 7-nanometer dual-band narrowband filter passes only the specific wavelengths emitted by hydrogen and oxygen gas inside nebulae — and blocks almost everything else, including most artificial light. What remains is signal. Clean, usable, beautiful signal, even from the middle of a suburb.
These Field Notes document what I've learned: the targets, the workflows, the scripts, and the honest results. Everything here was captured from Bortle 9. All the processing software is free.
Getting Started
Painting with Light You Can't See — An Introduction to Narrowband Astrophotography
What narrowband imaging is, why it works under light pollution, what equipment you need, and how to plan your first session. Written for complete beginners — no prior astrophotography experience assumed.
7 pages | Free download
The Notes
Field Note #1 — NGC 2237 Rosette Nebula & NGC 2244 Satellite Cluster
HOO Palette Workflow | Dual-Band OSC | Bortle 9 | February 11, 2026
16 minutes of integration. A Bortle 9 suburban backyard. A 7nm dual-band filter and a one-shot color camera. This Field Note covers the complete workflow from stacked master to finished HOO palette image — including the automated Siril processing script that brings the entire pipeline down to around 15 minutes of processing time.
Covers: HOO palette theory, OIII formula derivation, star separation architecture, GraXpert background extraction, Siril scripting, GIMP finishing, and target suitability guidance for light-polluted skies.
7 pages | Free download
Field Note #2 — NGC 2237 Rosette Nebula: Palette Comparison
Ha · HOO · SHO — Three palettes from the same 16-minute dataset
The same master.fits file, processed three ways. This note covers the physics behind each palette choice, the SII boost coefficient for synthetic SHO from dual-band data, and GIMP finishing tips specific to each palette.
9 pages | Free download
HOO & SHO Palette Workflow — Siril GUI Script v2.0.0
The Python script used in Field Note #1 and #2. Download to your computer and load via Script > Load Script in Siril. It presents a GUI dialog for all tunable parameters, and runs the complete HOO and SHO pipeline automatically — channel splitting, OIII derivation, StarNet star separation, independent stretching, palette composition, and output saving.
Requires: Siril 1.4.0-beta2 or later · sirilpy ≥ 0.6.37 · PyQt6 · StarNet
Python script | Free download
I hope you find these Notes useful. Processing the original Rosette Nebula image with HOO and SHO palettes was a game changer for me — understanding how much data was in the original image, and how much more beauty and wonder can be found.
Clear skies,
Pete