Astro Color Mixer: Targeted Colour Control

The workflow at a glance

Stage 1: Set up

1. Open the stretched image, launch the script. Script > CosgrovesCosmos > Astro Color Mixer.
2. Confirm the target image. It loads prominently; everything else refers to it.
3. Set the image mode. Starless unlocks mask softening. Say so explicitly.
4. Standard or Advanced. Advanced buys amplitude, Range Mask and passes.

Stage 2: Shape the band

5. Click the band on the wheel. Select Band is the default context panel.
6. Preview: Current Mask. Look before you touch a slider, every time.
7. Tune radius, feather, soften. Width, edge roll off, then blur (starless only).

Per band. Each band keeps its own radius and feather, so red can be narrow and hard while blue stays wide and soft.

Stage 3: Constrain by brightness

8. Enable the Range Mask. Everything before this was global. Now it is not.
9. Answer the pass prompt. Limit the current pass, or start a new one.
10. Probe the image for low and high. Click a pixel, read the cyan line on the histogram.
11. Set low, high and feather, then verify. Preview: Range Mask. Reopen the low end if it is thin.

Stage 4: Adjust

12. Hue, saturation, luminance. Only the pixels inside both masks respond.
13. Click and hold to compare. Before and after, judged on the image not the swatch.

Stage 5: Layer and commit

14. New pass, or save out. Next region gets its own pass. Masks export to PI.

Passes cost time. Each one adds another full resolution traverse when the result is committed back to PixInsight.

Two masks multiply, they do not compete

The band mask answers which hues are eligible. The Range Mask answers which brightnesses are eligible. A change lands only where both say yes, which is why the same red can be lifted in the faint outer dust and left alone in the core.

Fixed

• PixInsight 1.9.4 or newer, in the build that matches your processor.
• Nonlinear, stretched, already colour calibrated. This is polish, not calibration.
• Inspect the mask in Preview before moving any slider.
• Range Mask and passes belong to Advanced mode.
• Mask softening is offered in starless mode only. Blurring a mask with stars present hurts them.

Mine to judge

• Radius and feather per band. Narrow and hard, or wide and smooth.
• Whether Advanced amplitude is warranted, or whether it is just easier to overcook.
• Range Mask by preset or by probe. Probe wins on real data.
• How many passes before the slowdown outweighs the control.
• Whether a mask I built here is worth exporting for other PixInsight processes.