Integrating a luminance channel can help brighten and enhance an astrophoto. A luminance channel is either obtained using a luminance filter on the imaging rig or by extracting the luminance channel from an image after integrating RGB or Narrowband channels together, called a synthetic luminance.

This workflow demonstrates how to process luminance to improve your color images.

Pre-Requisites

To start the luminance processing, we need to have an integrated luminance image. If you are using a synthetic luminance, the image should be the extracted luminance channel immediately after integrating your color or narrowband channels.

If you used a luminance filter and captured a true luminance image, the aligned and preprocessed image should have gone through the following linear image processing steps

  1. Dynamic Cropped
  2. Background Extraction
  3. Noise Reduction with TGV Denoise
  4. Noise Reduction with Multiscale Linear Transform

Linear Image Processing

Linear image processing contains processes we do before permanently stretching the image (which becomes non-linear).

  • Deconvolution: Deconvolution improves the clarity in high-signal areas of the image.
  • Star Removal: The enhancements we make to bring out subtle detail in the luminance can negatively impact our stars. By removing stars, we can focus our attention on the signal. For star removal, I’m finding the best results with StarNet.

Non-Linear Image Processing

Most of the work on the luminance image happens in the non-linear (stretched) stage. This is where we can enhance details, improve contrast, and brighten faint regions.