Astrophotography Post-Processing: From RAW to Stunning

Here's what nobody tells beginners: every stunning astrophotography image you've seen has been heavily processed. This isn't cheating—it's revealing data that's actually in your image but invisible to the eye.

Camera sensors capture far more than monitors can display. A single RAW file contains 12-14 stops of dynamic range, but your screen usually only shows 8 bits (256 levels) of brightness. "Stretching" is the process of pulling the faint details of a nebula out of the dark background.

RAW straight-out-of-camera looks underwhelming. It's usually dark, lacks color, and has significant noise. That's perfectly normal. The post-processing phase is where the "art" of astrophotography happens.

The single biggest secret to clean images is Signal-to-Noise Ratio (SNR). Every time you take a photo, the camera sensor records real light (signal) and random electronic heat (noise).

By taking 10, 20, or 100 identical shots and "stacking" them in software, the random noise cancels itself out while the real light from the stars stays in the same place.

Free Stacking Software:

• Sequator (Windows) — Excellent and fast for Milky Way and landscape astro.
• DeepSkyStacker (Windows) — The classic for galaxies and nebulae.
• Siril (Windows/Mac/Linux) — Professional-grade tools for advanced users.

While every image is unique, here is the "Standard Operating Procedure" for processing a deep sky or Milky Way image:

1. Calibration & Stacking — Load your lights, darks, and flats into your stacking software to create a clean 'Master' file.

2. Background Extraction — City light pollution often creates a gradient (one side of the image is brighter than the other). Remove this first.

3. Color Calibration — Use a 'Photometric' tool or a manual white balance to ensure stars have their natural colors (blue, white, yellow, and red).

4. The 'Stretch' — This is the most critical step. Slowly pull the histogram sliders to brighten the nebula without blowing out the star cores.

5. Enhancement & Polish — Apply noise reduction, sharpen the fine details, and boost saturation in the nebulosity.

Eventually, you'll outgrow general-purpose photo editors.

PixInsight is built by astronomers, for astronomers. It treats your image as a data array. Tools like 'BlurXTerminator' and 'StarNet++' (which removes stars so you can edit the nebula separately) have revolutionized the hobby.

Photoshop is better for final 'artistic' touches—selective color grading, adding glows, and blending a dark-sky Milky Way over a sharp landscape foreground.