Starguide - A Practical Guide to Astro-Photography

PixInsight

Linear Image Processing

updated: 2025-10-14

Description and Purpose

Enhance the quality of the image:

• select relevant section
• correct any gradients or instrument 

There are different paths for post processing. For example you should first crop the image to discard unwanted sections of the picture and thereby reduce the size of the image files before further improving the image. But cropping the image first will also have the side effect that the geometry, picture area, pixel scale (arc seconds per pixel) settings etc. will no longer work correctly during the next steps. I therefore usually don't crop images at all.

Also instead of applying the Background Improvement steps the SPCC or PCC photometric color corrections can be used as they too handle background noise reduction. But which process is better suited for an image totally depends on the image itself, whether the sky conditions were good, enough light was collected etc.

Sub Chapters

• Step 1: Image Transformation
• Step 2: Gradient Correction
• Step 3: Deconvolution
• Step 4: Color Calibration
• Step 5: Noise Reduction
• Step 6: Optional Linear Processing Steps
• Step 6: Separating Stars and DSO Objects
• Step 7: Enhancing the DSO (Cloud) Image
• Step 8: Enhancing the Stars Image
• Step 9: Combining the DSO and Stars Image
• Step 10 (optional):  Hubble Palette Processing on Color Images

Input

The integrated linear Master Light frame from the Image Alignment and  Integration 

Output

An enhanced linear (unstretched), but not yet final image

Previous Step

Image Pre-Processing

Next Steps

De-Linearize the Image

Resource(s)

Linear Images on YouTube

Linear Image Processing Workflow

Final Stretch Workflow

file: Astro Image Processing Overview

Original image from image integration

Linear but not final image after quality enhancements