A streamlined narrowband processing workflow

Open a non-linked screen transfer function and auto stretch the integrated master. This is a look only step that reveals what the data is hiding. On this set the auto stretch exposes a strong gradient running bright at the bottom right and fading toward the top left.

Run spectrophotometric flux calibration before touching the gradient. This puts the channels on a sound photometric footing. Read the residual figures it reports, smaller numbers mean better quality data.

Apply multiscale gradient correction. It compares the image across several scales, separates real signal from the gradient, and removes the gradient cleanly. Expect a small loss of saturation in the nebulosity, which you recover later.

Run BlurXTerminator in correct only mode. This is the recommended first pass. It corrects the stars to round without yet sharpening or shrinking anything, which sets a clean base for colour work.

Use the SETI Astro find background script to place a background sample, then run colour calibration with background neutralisation. Pull a background region from a preview and apply it to the image. Configure the red, green and blue inputs for your sensor and filter.

The image will look alarming straight after calibration. That is expected behaviour from spectrophotometric colour correction. Re-run the screen transfer function, this time linked, and accurate colour appears. Discard the background sample once done.

Run BlurXTerminator again in its default mode. This tightens and slightly shrinks the stars and gently sharpens the non stellar detail. The change in the stars is the obvious win on this target.

Run NoiseXTerminator while still linear. Back the strength off from the default. A lighter touch handles the colour noise more gracefully and leaves fewer artefacts behind, and you can always add more later.

Stretch with multiscale adaptive stretch. It handles a wide range of targets well from the defaults with little tweaking. Dim the background slightly and lift the aggressiveness a touch to make the nebula stand out, but keep a light hand.

Run SCNR to suppress the green cast. The effect is quiet but real. Stars that carried a greenish tint shift back toward a natural blue.

Remove the stars with StarXTerminator to produce a starless image and a separate star image. Processing the two independently is the core of the finish, since the halos and the structure want different treatment.

With the stars gone, filter and glass halos are easy to target on the starless image. Use the SETI Astro blemish blaster script, shift and click to ring each problem area, then execute. Three small circles process quickly, larger ones take longer.

Use generalised hyperbolic stretch on the starless nebula in two to four small passes, working different parts of the histogram each time. Set the symmetry point near the base of the curve where it begins to flatten, so everything above it lifts. Finish with one gentle contrast pass that brightens only the brightest regions.

Apply local histogram equalisation for texture and local contrast in the nebulosity. It brightens some regions and darkens others, giving the structure more depth.

Unsharp mask is optional and target dependent. On smooth data it can over contrast the dark lanes and it always adds noise. If you use it, keep it light, and judge it zoomed in rather than at full frame.

Run NoiseXTerminator once more to clear the noise reintroduced by the stretches and any sharpening. Set a preview on the brightest part of the nebula and compare before and after to find the right level.

Recombine with the rescreen stars script. Drag and drop, set the starless view as the nebula and the star view as the stars, and create a new image. There is nothing else to set. Use the matching star reduction script first if the stars need taming.

A light curves transformation to finish. Lift the saturation a touch and add a small chrominance boost to deepen the blues and reds. Chrominance is powerful, so a tiny amount goes a long way.