As we veer into autumn, Lagoon's only above the horizon for an hour or so after astronomical dark. Two nights of exposures led to this.

1 stack of 90 images, Canon 800D at ISO 800, Pentax 135mm f2.5 lens at f4, 30s exposures, tracked with Omegon minitrack lx2. a couple dozen darks, 120 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 = 10)

* weighing: (15*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin)) + 35*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin)) + 20*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin))+30

* img 2762 ref

* generalized student ESD rejection, remove range_low 0.2

* drizzle integration

***** Linear processing

*** LinearFit on channels, then combined

*** Rotate to vertical

*** color calibration

*** Denoised - EZDenoise, TGV decrease exponent by -1

***** Nonlinear processing

*** Initial stretch

* EZStretch

* SNCR 0.8

*** Fix halos

* Channel extract, lagoon_B - (lagoon_G + lagoon_R)/2 = blue_mask

* stretch blue mask shadows 0.04 mids 0.08

* with masks on, SNCR blue, SNCR green

** MLT processing

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

*** First iteration (detail)

* extract 3 MLT layers, diff, mask diff with original luminance, stretched shadows 0.05 mids 0.35

* lagoon mask: iif (

inellipse(2798, 8022, 200,200) ||

inellipse(2175, 9654, 400, 300),

lagoon_L,

0

), blur 6 MLT layers, stretch shadows and mids 0.15, blur again, save

* with lagoon mask on, dark structure enhance on diff, 7 layers, 3x3 (left * (1 - nebula_mask) + left_clone * nebula_mask since DSS doesn't like existing masks)

* with luminance mask on, curves modify diff (slight s-shaped curve in luminance with small deep dip in lows and low slow boost in mids and highs, saturation boost)

* pixelmath back together, normalized

** Second iteration (largescale nebula)

* extract 4 MLT layers, diff, mask diff with own luminance, stretched mids 0.15

* curve boost luminance, saturation, with mask on

* mask out, DSS 7 layers 3x3 0.5 amount

* color saturation lower sat in oranges, rise in blues and reds

* pixelmath back together, normalized

** Third iteration (major milky way)

* extract 8 MLT layers, diff, mask with own luminance stretched mids 0.25

* curve boost luminance, saturation

* pixelmath back together, normalized

*** Finishers

* LHE 512, contrast 1.5, meld lagoon_L * lagoon + (1 - lagoon_L) * (lagoon + lhe) / 2

* LHE 256, contrast 1.5, meld lagoon_L * lagoon + (1 - lagoon_L) * (lagoon * 2 + lhe) / 3

* background neutralize ROI left 1500 top 1800 widht 1500 height 1200

** split into stars and starless with Starnet, process stars as follows

* invert, SNCR green, invert again - fixes CA halos

* morphological transformation, erosion, 6x0.2

* curves boost saturation

* add starless back again

* on full image, MMT sharpen - 6 layers, biases 0.05 0.05 0.025 0.025 0.012 0.005