A revisit of my old Eon heart - this time, an iOptron mount and a Swanwick, rather than Harrison reference

Processing details:

1 stack of 86 120s images, Canon 800D at ISO 800, Canon 50mmf1.8 lens at f4, iOptron Skyguider Pro tracker. 50 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 = 8)

* Approval: SNRWeight > 5.4 & FWHM < 2 & Eccentricity < 0.6

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

+ 15*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))

+ 30*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)

+ 40

img 0469 ref

* ESD integration

* drizzle integration, gaussian kernel

*****Linear processing

*** Initial

* Crop

* DBE tolerance 3, avoiding the milky way

*** Color calibration

* PCC centered on Sadr, 50mm FL 2um pixel, background neutralization on lower left dustcloud, upper limit 0.005

* Fix CA: autostretch luminance, create starless version (starnet + clonestamp), substract from luminance to get the star_mask, bump RGB/K with curves, 1 dilation w/ morphological transformation, 1 convolution - sncf_star_mask

* Invert original image, apply mask to uncover only star cores, SNCR 0.9 green w/ preserve luminance

*** Deconvolution

* Background mask: EZDecon generated off the starless version

* PSF: EZDecon generated

* star mask: take sncf_star_mask, boost, dilate 1x, boost again - decon_star_mask

* 25 iterations

*** Denoise

* EZDenoise implementation of Jon Rista's method, TGV edge protection 8e-6, regular MMT

***** Nonlinear procesing

*** Initial stretch

* MaskedStretch, default settings

* Luminance: using itself as mask, curves

* Chrominance: ACDNR stdev 2 3 iterations structure size 5, lightness mask

* LRGBCombine with saturation 0.35, chrominance noise reduction

*** Starless/stars separation

* Chroma starless separation ends up producing far more artefacts, so let's see if this can be fixed

* extract luminance and create starless version. Clonestamp the very few problems - starless_L

* create starless version of colored version, clonestamp the largest stars - starless. Extract luminance.

* 0.5 - (starless_L - starless_L1) = diff (to be used later)

* split starless into cielab. Throw away luminance since we'll use the one off the monochrome

* Tone down blue halos (what's left of my CA) clone blue, stretch shadows 0.45 highs 0.67 mids 0.36 - starless_b_stretched. Rannge mask lower limit 0.52 fuzziness 0.05.Blur 3 layers of a trous. Histogram transform highs 0.75 mids 0.75. blur 3 layers of a trous again. save as blue_halos. Apply on starless_b. Curve fix away the blue halos - we'll handle them in the star image

**** Starless processing:

***MLT stretch

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

**Initial (fine details)

* created a new multiscale linear transform, kept 4 layers using linear interpolation

* diffed from original image to create a "blurred" version of original image

* extracted luminance from original, histo stretch high 0.5 mids 0.3 used as mask on blurred version

* used curves to pump up luminance, saturation

* colorsat pump up reds/pinks and teal blue, desat yellows and greens (wtf, my white balance...)

* pixelmath sum the 3, rescaled, back to original image

**Second (nebula colors)

* new multiscale linear transform, keep 5 layers

* diff from original

* extract luminance from blurred image, to use as a mask

* masked blurred image with its own luminance (stretched once high 0.5 mids 0.4, second highs 0.9 mids 0.3) gave it big bost in RGB, slight dip in green, big boost in saturation.

* pixelmath sum the 3, rescaled, back to original image

*** Starless finishers

* slightly downcurve green

* LHE kernel 512 contrast limit 1.5 mix 0.33 * lhe + 0.67 * starless

* LHE kernel 256 contrast limit 1.5 mix 0.25 * lhe + 0.75 * starless

*** Stars:

* desaturate blues slightly

* extract luminance to use as star mask later

* sum back up with starless

*** Finishers

* Star reduction using the previous star mask, erase the big stars with clone stamp, and apply ez star reduce on morphological reduction, 8 iterations

* MMT 6 layers, biases 0.05 0.05 0.025 0.025 0.012 0.005