Westerhout 5 in Cassiopeia

The Soul Nebula is a huge emission region in Cassiopeia, often photographed in a group with the Heart Nebula. It’s sometimes listed as IC1848, but that apparently refers to the embedded star cluster. In addition to the designation Westerhout 5, it’s listed as Sharpless 2-199 and LBN 667. The upside-down turkey head-like region at left is IC1871. This is a tricolor narrowband image.

Exposure: Total exposure time 20 hours, 20:17:23 SII:Ha:OIII. All bin 1x1. Captured from October 2018 to January 2019, and again in August 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: FWHM of subs about 2.4 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.9 arcsecs/pixel

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon 5nm Ha/SII, 3nm OIII, Type IIe LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.0.0.8
Guide SW: PHD2.6.6, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2
Processing Workflow by Workspace in PixInsight 1.85

1. Calibration
BatchPreProcessing with flats, darks and bias, using Cosmetic Correction with master dark

2. Stack and Mure Denoise
Blink to preview and reject a few frames
Subframe Selector to confirm selections
Image Integration
Mure Denoise
Dynamic Crop

3. Linear Processing
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask (on Ha and SII only)

4. Stretching
Histo Trans
Curves Trans
Ha only: Exponential Trans on background, using a mask
Ha and SII only: Local Histogram Equalization on core
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred range mask to protect highlights

5. Color merge
Merged narrowband channels in ChannelCombination, mapping SII:Ha:OIII to R:G:B
Color shifting toward blue-gold:
Color Mask script (magenta mask to remove magenta halos, then green, cyan and yellow)
Curves to shift colors, using each mask
Extract luminance, then apply mild Local Histogram Equalization and HDR Multiscale Transform to enhance contrast

6. Star Reduction
Remove stars with Starnet++ Pixinsight process. I used a mask made in Photoshop to protect some bright transition areas.
Create new version of image with less stretching to control star sizes
With PixelMath max command, add star image to starless image

7. Final
Mild Curves Transformation
Slight Multiscale Linear Transform to sharpen bright transition areas
TGVDenoise to remove remaining noise
sRGB
Downsize 50% and save as JPG