Beginner’s Guide to Post-Editing a Stacked Comet Image in Affinity Photo V2

 Beginner’s Guide to Post-Editing a Stacked Comet Image in Affinity Photo V2

With the free of Affinity Photo 3, I know many astrophotographers are considering the switch across from Photoshop. I have been using Affinity Photo for two years now and this is my workflow for processing a comet image.

Tools Used:

·       Develop Persona (for RAW files)

·       Photo Persona (main editing workspace)

·       Layers, Masks, Curves, Levels, HSL, and Noise Reduction filters

If you want to know how to capture a comet image - these previous posts may help: 

https://undersouthwestskies.blogspot.com/2025/10/a-beginners-guide-to-photographing.html

https://undersouthwestskies.blogspot.com/2025/11/imaging-session-chasing-comet-lemmon.html 

https://undersouthwestskies.blogspot.com/2025/11/beginner-tutorial-how-to-stack-comet.html

 

Workflow

If working from a single RAW file:

Start at Step 1 (Develop Persona).

If importing a stacked FITS/TIFF image:

Open the file directly into Photo Persona, but still follow the adjustments from Step 2 onward.

 

1. Prepare Your Image in the Develop Persona (RAW files only)

These steps set a clean starting point before moving to the main editor.

• Exposure: Pull back highlights if the comet nucleus looks blown out.
• Black point: Increase slightly to deepen the sky background.
• Contrast & Clarity: Keep very low — high values exaggerate noise.
• White Balance: Neutral or slightly cool for a natural comet colour.
• Lens Corrections: Enable chromatic aberration and vignetting corrections.

Click “Develop” to enter the Photo Persona.

 

2. Clean Up the Background & Frame the Image

This stage sets your sky background and composition before isolating the comet.

a. Crop & Rotate

Straighten the frame and position the comet creatively (e.g., rule of thirds or aligning the tail diagonally).

b. Duplicate the Base Layer

Right-click → Duplicate.
Having a backup layer is always useful.

c. Remove Gradients / Light Pollution

Choose one approach:

• Manual tools:
  Use the Inpainting Brush or Clone Tool to smooth bright areas near the horizon.
• Curves + Mask method:
• Add a Curves Adjustment Layer
• Invert its mask
• Paint white on the mask where gradients occur
• Gently darken those regions
• External tool:
  Software like GraXpert often produces excellent gradient removal results, then you re-import the cleaned image into Affinity.

This gives you a clean sky to work with before enhancing the comet.

 

3. Isolate and Enhance the Comet

This step ensures that adjustments to the comet don’t accidentally affect the stars or sky.

a. Select the Comet

Use the Selection Brush Tool or Freehand/Pen Tool to outline the comet and tail.

b. Feather the Selection

About 10–30 px, depending on image resolution.

c. Create a Masked Layer

Right-click → New Layer with Mask.
Now you have a specific “Comet Layer” for targeted editing.

d. Enhance the Comet

• Curves: Lift midtones and highlights slightly to brighten the tail and nucleus.
• HSL:
• Slight saturation boost (5–10%)
• Subtle hue shifts if you want to emphasise green/blue tones in the coma
• Detail Enhancement:
  Use Unsharp Mask or the Clarity filter, gently:
• Radius: 1–2 px
• Amount: ≤ 30%

This should bring out tail structure without creating halos.

 

Comet Lemmon october 2025

Images snatched between cloud breaks 

4. Control Stars & Background

Comets often benefit from reducing the prominence of surrounding stars.

Option A — Using Plugins

If you have the James Ritson astrophotography macros/plugins for Affinity (or similar tools), apply the star-reduction macro here.

Option B — Manual Star Softening

A simple technique: 

1. Duplicate your background layer.
2. Apply Gaussian Blur (≈ 3–5 px).
3. Change the layer’s Blend Mode to Darken or Soft Light.
4. Mask out the comet so it remains bright.

This subtly reduces star intensity without removing them.

Optional: Boost Star Colour

Use HSL or Selective Colour, applied through a mask targeting only the star field.
Increase saturation very gently for natural, pleasing star colours.

 

5. Final Colour & Contrast Refinements

These global adjustments tie the whole image together.

• Curves: Add a subtle S-curve to improve overall contrast.
• HSL or Selective Colour:
  Adjust the sky tone — aim for a natural, slightly cool deep grey/blue-grey rather than pure black.
• Levels:
  Bring the black point inward carefully. Avoid clipping faint comet tails or dust structures.

 

6. Noise Reduction & Final Polish

Noise typically increases after gradient removal and enhancement steps, so save this for last.

1. Merge a copy of the visible layers (Right-click → Merge Visible).
2. Apply Reduce Noise (Filters → Noise → Reduce Noise):
• Luminance: ~30–50%
• Colour: ~20–40%
• Preserve Details: ON

You can also use a mask to apply noise reduction only to the background, keeping the comet sharp.

 

A second version of my Comet Lemmon image 

7. Exporting Your Final Image

Choose output format based on purpose:

• TIFF (16-bit): Best for scientific, archival, or further processing.
• PNG or JPEG: Ideal for sharing online (JPEG quality ~95%).
• Use sRGB profile for web posting.

 

Optional Advanced Techniques

• Comet/Star Combination:
  Blend a comet-tracked stack with a star-tracked stack using Lighten or Screen blend modes for the best of both worlds.
• Affinity Astrophotography Stack (V2.4+):
  Affinity now supports astrophotography stacking natively, including star alignment and median stacking — useful for producing a cleaner starting point before editing.

 

Final Thoughts

Affinity Photo V2 is a powerful, affordable tool for comet processing, and once you get comfortable with masking and adjustment layers, you’ll find it capable of professional-quality results.
Working slowly, keeping edits subtle, and masking carefully will help your comet images look clean, natural, and visually striking — perfect for sharing or printing.

Of course, as a beginner myself, Affinity Photo is still something I have to master. Masking is my Achilles heel – rather frustratingly!

As always, do you have a different work flow? What do you do differently? What additional tips would you add in here? Drop us your tips, thoughts, observations in the box below. 

Clear skies and take care out there, and as always, have plenty of fun! 

Steve