Astro Color Mixer
A browser-based beta tool for refining hue, saturation, and luminance in stretched RGB astrophotography images.
Viewing note
This builder is usable on smaller screens, but the full layout is easiest to view and work with on a desktop or laptop display.
Astro Color Mixer
Astro Color Mixer is a nonlinear RGB color refinement tool I built for astrophotography. The goal is not to replace PixInsight, Photoshop, or the normal processing workflow, but to give astrophotographers a more focused way to make controlled color and luminance adjustments after an image has been stretched.
I have always been frustrated by the tools currently available in PixInsight for color manipulation and late-stage image polishing. I often use the Photoshop Camera Raw Color Mixer and its real-time hue, saturation, and luminance controls, but I have also been frustrated by its limitations for astrophotography. This tool is inspired by that capability, but adds elements that make it more astro-friendly.
The tool works around practical astrophotography color regions: H-alpha reds, OIII/cyan regions, blue reflection nebulosity, warm dust, galaxy cores, neutral background areas, and common cleanup zones such as magenta halos or green casts. It also includes Range Masking, refinement passes, a histogram, polar color plot, and probe tools so adjustments can be made with visual feedback rather than guesswork.
This is still a beta tool, but it reflects the kind of color work I often find myself wanting to do late in processing: broad adjustments first, then more targeted refinements without losing track of what is being affected.
This web app began as a prototype for my first PixInsight tool. I decided to share it here in this form for those interested in trying the workflow directly in the browser.
What to know before using the tool
Astro Color Mixer includes built-in FAQ and Technical Appendix buttons in the upper-right corner of the app. Those provide more detailed guidance on the workflow, Range Mask behavior, image modes, diagnostics, and the underlying processing model.
Start with a nonlinear RGB image
This tool is meant for images that have already been calibrated, integrated, color-balanced, and stretched. It is not intended for raw linear masters, calibration work, background extraction, or initial color calibration. This prototype accepts TIFF or PNG files as input.
Think late-stage refinement
Astro Color Mixer is best used after the image already has a reasonable global look. It is for controlled color and luminance shaping: strengthening faint color, taming halos, adjusting dust or galaxy tones, working on neutral background areas, and making targeted refinements.
Choose the right image mode
Use Stars Present if the image still contains normal stars. Use Starless / Star-Reduced if the stars have been removed or strongly reduced. The setting does not remove stars; it changes how conservatively the tool protects bright stellar structures.
Use small moves first
The sliders can make strong changes quickly. Start with modest adjustments, inspect the preview, and use the mask views, histogram, polar plot, and probe to understand what is being affected.
Standard vs Advanced
Standard mode is for broad color work. Use Advanced mode when you want refinement passes, Range Mask targeting, and more surgical changes.
Range Mask needs care
Range Mask limits changes by brightness. It is useful for backgrounds, faint nebulosity, highlights, galaxy cores, or halos, but it depends heavily on the image’s existing stretch. Always inspect the histogram and mask behavior before making strong changes.
The preview is guidance
The app uses preview-resolution data for speed. Saved output is rendered at full resolution, so the final result should match the intent, but the preview is still an approximation.
Nothing leaves your browser
For the web version, image work is handled client-side in the browser. Large TIFF files may still be demanding, depending on image size and available memory.
Saving your result
When adjustments are complete, use the Save Image button to export the final result. The saved image is rendered at full resolution and can be saved as a TIFF or PNG.
in the upper-right corner, which provide more detailed guidance on the workflow, Range Mask behavior, image modes, diagnostics, and the underlying processing model.
Pixinsight Version
This PixInsight versio of this tool is under develpment. Stay tuned for more info when available.
