Crest of the Horse's wave. The Flame fading from emission to reflexion to dust. Vanishing stars, and Alniram's blue light sculpting dust pillars; an echo of the Witch's head. And the deep is never black in Orion.

1 stack of 110 30s images, Canon 800D at ISO 800, Canon 400mm f5.6 lens wide open, iOptron Skyguider Pro tracker. 100 darks, 350 biases. Processed in PixInsight as below

***** Integration

lightvortexastronomy tutorial (https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html)

* CC defect list + master dark (sigma = 8)

15*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin))

+ 35*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))

+ 20*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)

+ 30

* img 6098 ref

* generalized ESD integration, low range cutoffs of 0.02

* drizzle integration, gaussian kernel

*****Linear processing

*** Initial

* Crop

* DBE tolerance 3, division mode

*** Color calibration

* Color calibration using background reference a portion below Alnitak

* Photometric CC for finetune

*** Denoise

* EzDenoise, TGV edge protection 2e-5, MMT by default

***** Nonlinear processing

**** Luminance

*** Initial stretch

* Extract luminance

* EZSoftStretch median 0.3 expand lower 0.05

*** Starnet processing:

* separate in starless vs stars

* clonestamp the two dust spots in starless image

** Starmask creation for later chroma processing

* range mask 0.95-1, blur with 4 layers of a trous - range_mask

* create chroma_star_mask to use later - stars + range_mask

*** Secondary stretch

* EZHDR

* Histo stretch shadows 0.15 mids 0.4

*** EZDenoise TGV edge 3e-2, MMT default

*** Contrast adjustations

* Histo stretch shadows 0.9 mids 0.2, twice

**** Chroma

*** Initial stretch:

* arcsinh stretch factor 1000 black point 0.000463

* SNCR green 1

* arcsinh stretch some more - stretch factor 3 black point 0.05

*** pink star fix

* split into channels

* on green channel,with chroma_star_mask_on, pixelmath max(belt_G, (belt_B + belt_R)/2)

* clone stamp some artefacts on brighter stars

* recombine

*** small fixes:

* denoise ACDNR on chroma only, lightness mask, SD 4 6 iterations

****Recombine

* LRGB on luma and RGB channels of chroma, saturation 0.3

**** Starnet processing

* split into starless and stars, start working on starless

*** Color fixes

* split starless in RGB channels,

* desaturate blue star halos: blue_mask = starless_B - starless_R with Flame clonestamped out. With this on, desaturate w/curves strongly - top sat at 40%, log-like curve

* saturate Horsehead: red_mask = starless_R - starless_G with everything but Horsehead clonestamped out. Histo stretch shadows 0.019 highs 0.5 mids 0.4. With it on, raise saturation a lot, and lightness slightly - poor man's Halpha mod

* desaturate background: extract luminance, histo stretch shadows 0.12 highs 0.25 mids 0.2, blur 4 layers w/ A Trous - nebula_mask. Apply inverted, desaturate with curves (50% max sat, log-like curve)

***MLT stretch

http://www.stelleelettroniche.it/en/2014/09/astrophoto/m42-ngc1975-multilayer-processing-first-part/

** Initial (fine details)

* MLT, keep first 8 layers (because large halos), erase Horsehead&Flame with clonestamp. Diff.

* Extract luminance from starless, shadows 0.08 highs 0.6 mids 0.25

* S-shaped luminance curve, add some saturation to diff, with luminance mask

* sum back together original + mlt + diff, rescaled

** Secondary (large details)

* MLT, keep first 8 layers, don't erase anything, diff

* Extract red channel from diff, initial stretch shadows 0.05 mids 0.65, secondary shadows 0.02 high 0.5 mids 0.3

* with red channel mask on diff, use curves to boost sat and RGB

* sum back together original + mlt + diff, rescaled

*** Add the stars back together

**** Single-image processing

***EZStarReduction, Adam Block, 2x

***final color fixes

* create starless version

* blue mask = starless_B - starless_R with flame and some other nebulae clonestamped out. Desaturate blue to 0.33 with curves. Desaturate again to .75

*** Denoising

*EZDenoise, TGV edge 0.1e-2, MMT default

* ACDNR chrominance-only, lightness mask, stdev 4, 6 iterations

*** Finishers

* Dark structure enhance, 8 layers, scaling function 5x5 b3 spline, 0.4 amount

* Dark structure enhance, 8 layers, scaling function 3x3 linear interpolation, 0.2 amount

* MMT sharpen, 6 layers biases 0.05 0.05 0.25 0.025 0.12 0.005

* Integer downsample 2x