So I originally shot this back in 2020 from my in-law’s house in a Bortle 4 area. Only got a handful of LRGB subs because my guide cam did not wanna talk to my laptop for most of the session back then. Recently I decided to shoot some Ha from my B9 apartment and give it a reprocess in HaLRGB. Overall I’m very pleased with this improvement after 6 years! Captured captured in February 2020 and December 2025 from bortle 4 and 9, respectively.

Places where I host my other images:

Flickr | Pixelfed

Equipment:

• TPO 6" F/4 Imaging Newtonian

• Orion Sirius EQ-G

• ZWO ASI1600MM-Pro

• Skywatcher Quattro Coma Corrector

• ZWO EFW 8x1.25"/31mm

• Astronomik LRGB+CLS Filters- 31mm

• Astrodon 31mm Ha 5nm, Oiii 3nm, Sii 5nm

• Agena 50mm Deluxe Straight-Through Guide Scope

• ZWO ASI-290mc for guiding

• Moonlite Autofocuser

Acquisition: 9 hours 55 minutes (Camera at unity gain, -15°C)

• Ha - 48x600"

• L - 12x300"

• R - 4x300"

• G - 4x300"

• B - 3x300"

• Darks- 30

• Flats- 30 per filter

Capture Software:

• Captured using N.I.N.A. and PHD2 for guiding and dithering.

PixInsight Preprocessing:

• BatchPreProcessing

• StarAlignment

• Blink

• ImageIntegration per channel

• DrizzleIntegration (2x, Var β=1.5)

• Dynamic Crop

• DynamicBackgroundExtraction

duplicated each image and removed stars via StarXterminator. Ran DBE with a shitload of points to generate background model. model subtracted from original pic using the following PixelMath (math courtesy of /u/jimmythechicken1)

$T * med(model) / model

Luminance linear:

• BlurXterminator

• StarXterminator to completely remove stars (extracted stars processed separately)

• STF applied via HistogramTransformation to stretch nonlinear

Ha Processing:

• StarX to remove stars

• Subtracted red continuum to create a ‘clean’ Ha image using pixelmath

• Pixelmath to combine the clean Ha image into the RGB image

largely following this advanced narrowband combination guide, also made by jimmy

RGB Linear:

• Channelcombination to make color image from RGB stacks

• SpectrophotometricColorCalibration

• StarX to remove stars (to be used for star addition later)

• PixelMath per the advanced narrowband guide to add Ha into the red and blue channels

• ArcsinhStretch + HistogramTransformation to stretch nonlinear

• Slight curves saturation boost and histogram adjustments

Stars only image:

• BlurXterminator for discortion correction and some mild star reduction

• HSV repair

• ArcsinhStretch + HistogramTransformation to stretch nonlinear (less aggressive stretch)

• Slight curve adjustments

Nonlinear Processing

• LRGBCombination to combine stretched RGB and L images

• DeepSNR Noise reduction

• Shitloads of curve transformations to adjust luminance, contrast, saturation, etc

• More curves

• LocalHistogramTransformation

• Pixelmath to add in the stretched stars only image from earlier

  This basically re-linearizes the two images, adds them together, and then stretches them back to before. More info on it here

  mtf(.005,

  mtf(.995,Stars)+

  mtf(.995,Starless))

• NoiseXTerminator for some small scale chrominance noise reduction

• Resample to 70%

• DynamicCrop in on just the galaxy (not a whole lot going on in the background)

• Annotation

Great image and thanks for sharing all the details too.

I’m always curious about how does one decide the number of images of the various filters. They’re never 1:1:1…