The Core PixInsight Workflow (OSC)

Rig context: ASI585MC Air or Seestar data on the FRA400 or 107PHQ, captured through ASIAIR, stacked in WBPP or Siril. PixInsight 1.9.x with the RC Astro suite (BlurXTerminator, StarXTerminator, NoiseXTerminator). MultiscaleAdaptiveStretch ships with PixInsight; ImageBlend is a free add-on.

The workflow at a glance

Stage 0: Open and solve

1. Open the cropped master, auto STF. Ctrl/Cmd+A. Close any crop mask that opens beside it. Ugly colour is normal.
2. Plate solve if not already solved. Script > Image Analysis > ImageSolver. SPCC will not run without it.

Stage 1: Flatten and calibrate

3. DynamicBackgroundExtraction. Samples on empty sky, Tolerance 1 to 2, Subtraction for light pollution. MGC for frame-filling nebulae.
4. SpectrophotometricColorCalibration. Pick the real filter per channel. Dual-band: Photon Flux white reference. Unsure: defaults.

Stage 2: Correct, sharpen, separate

5. BlurXTerminator, Correct Only. Rounds stars, fixes colour offsets, no sharpening. Run on everything.
6. BlurXTerminator, nonstellar only. Sharpen Stars 0, Halos 0, Sharpen Nonstellar 0.50 to 0.90 by target.
7. StarXTerminator, generate star image. Unscreen off (linear). Rename windows stars and nebula immediately.

Stage 3: Denoise

8. Over-stretch the screen to see the noise. STF: zoom the histogram, black point right, midpoint left. Preview only, nothing is changed.
9. NoiseXTerminator. Iterations 5. Both separation modes on, sliders from zero: HF Colour, HF Intensity, LF Colour, LF Intensity.

Stage 4: Stretch

10. Stars: STF into HistogramTransformation. Drag the STF triangle to the bottom bar of HT, apply to stars, reset both.
11. Starless: MultiscaleAdaptiveStretch. Screen stretch OFF first. DRC 0, tune Aggressiveness and Target Background, Colour Amount low.
12. CurvesTransformation, light touch. Optional. RGB/K contrast, per-channel balance. Finishing only.

Stage 5: Recombine and save

13. ImageBlend, Screen mode. Base = starless, Blend = stars. Midtones below 0.5 bigger stars, above 0.5 smaller.
14. File > Save Project. Tidy the desktop, keep every window open, save beside the master as Target v1.
15. Export. 16-bit TIFF master, then JPEG at quality 100 into the JPEG folder.

Optional: the TIFF from step 15 is the hand-off to Photoshop or Affinity for colour, contrast and texture work. Do that on the starless layer, bring it back, and recombine the stars in ImageBlend as in step 13.

Two habits that make everything else work. The blue tick on each tool must be on and the image you want to edit must be the last one clicked. And use the undo and redo arrows after every step: if you cannot see the improvement, question the step.

The logic in one line

Gradients out before colour is fitted, deconvolution before any noise reduction, stars out before the hard stretch, and nothing permanent happens to the pixels until step 10.

Non-negotiable

• Astrometric solution in the header before SPCC.
• Gradient removal before SPCC, not after.
• BlurXTerminator before NoiseXTerminator. Never sharpen smoothed noise.
• BXT, StarX and NXT all run on linear data.
• Screen stretch off before MultiscaleAdaptiveStretch.
• Reset STF and HT after the star stretch or the next preview will blow out.
• Save Project before closing any window.

Your call

• DBE versus MultiscaleGradientCorrection. DBE when there is clean sky to sample; MGC when the nebula fills the frame.
• Subtraction or Division in DBE. Decided by the residual, not the site.
• Sharpen Nonstellar amount. 0.90 on soft dust, 0.50 to 0.60 on hard filaments.
• The NXT single-slider route versus the four-slider manual route.
• MAS Aggressiveness, Target Background and how much saturation to leave for later.
• Star weight in ImageBlend.