Image processing for astrophotography

The data and the Siril script can be found in this google drive folder: https://drive.google.com/drive/folders/1vW2kqUQbHBEYf9KfGACMadruxLblsAUO

• Go to: https://siril.org/download/
• Download the installer for your operating system.
• Install:
  • Windows → run the .exe
  • macOS → open .dmg and move Siril to Applications
  • Linux → use AppImage or package manager

• Download StarNet++ from the provided link.
• Extract the folder to a known location (example: C:/Siril/Starnet2/).

• Download the provided script.
• Place it in your Siril scripts directory:
  • Windows → C:\Users\<user>\AppData\Local\Siril\scripts\
  • macOS → ~/Library/Application Support/siril/scripts/
  • Linux → ~/.config/siril/scripts/

• Download the dataset from the provided Drive link.
• Extract everything into a working directory.

The data is already calibrated. Only light frames are provided.

Create the following folders:

• L/
• R/
• G/
• B/
• HA/

Move each filter’s images into its respective folder.

• Open Siril.
• Click the Home (house) icon → top-left corner.
• Navigate to the parent directory that contains the subfolders: L, R, G, B, HA.
• Select that directory.

• Go to Scripts tab.
• Select the installed script.
• Siril begins checking and preparing images.
• Preview window appears.

To change preview mode:

• Bottom bar → switch Linear ⇄ AutoStretch.

• Go to Process → Background Extraction.
• Place sample points on dark, empty background areas.
• Ensure no stars, nebula, or bright zones under the points.
• Click Apply (Extract Background).

• Go to Analysis → Astrometry → Plate Solver.
• Enter:
  • Focal length
  • Pixel size
  • Camera sensor information
• These values are visible under Image Information.
• Click Solve.

• Go to Color → Photometric Color Calibration.
• If Gaia server is down → download Gaia catalog locally from Siril’s database manager.
• Run SPCC.

Stretch *before* star removal for best results.

• Go to Image Processing → Histogram Transformation.
• Use AutoStretch or adjust:
  • Black point
  • Mid-level
  • White point
• Apply the stretch.

• Go to Process → Star Removal → StarNet++.
• Set the StarNet++ executable path if prompted.
• Enable:
  • “Create starless image”
  • “Create star mask”
• Run StarNet++.

Output:

• One starless image
• One stars-only image

• Go to Color → Saturation.
• Increase moderately.

• Go to Image Processing → Curves.
• Adjust luminance/RGB to preference.

• Go to Image Processing → Star Processing → star recomposition.
• Combine:

``starless + stars``

• Apply to produce the final image.

• Go to File → Save As.
• Export as TIFF, PNG, or FITS.