Spiral Galaxy Messier 100 in Coma Berenices

LRGB Image. The satellite galaxies are magnitudes 14 to 16, but the image contains many faint background galaxies, mostly reddish, down to at least mag 19.


Exposure: Total exposure time about 12.8 hours, Lum 208 x 2 mins, R/G/B 65/51/60 x 2 mins. All bin 1x1. Captured over 13 nights in April-May 2016 and April-May 2017.
Light pollution: Bortle 8 (white zone, NELM about 4.5)
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/pixel (50% reduction)

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: CPC1100
Camera: SXVR-H694
Filter wheel: Atik EFW2 with 7x1.25 carousel
Filters: Astrodon Type IIe LRGB
Rotator: Optec Pyxis 2" (2017 images only), connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB_nStep with driver version 6.0.7
OAG: Celestron OAG
Guide cam: Lodestar (first generation). 1 second exposures
Automation SW: Sequence Generator Pro
Guide SW: PHD2
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 and weight by FWHM and SNR
Image Integration
Mure Denoise (this worked on blue stack only; it had basically no effect on Lum, Green and Red. Not sure why)

3. Luminance Linear Processing
Dynamic Crop
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask support

4. Luminance Stretching
Histo Trans
Curves Trans
Noise Reduction with TGV Denoise and Multiscale Median Transform (following David Ault’s Astro Imaging Channel tutorial).
Local Histogram Equalization to enhance contrast inside galaxy core

5. RGB Linear Processing
RGB Combination to merge RGB channels
Dynamic Crop (using the same icon as with luminance)
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Simple STF stretch applied via Histo Trans
TGV Denoise

7. Color
Merged Lum and RGB in LRGB Combination, boosting saturation
Extensive touchup in Photoshop with Channel Mixer on selected areas to eliminate excessive green patches and blue comatic halos

8. Final
Star shrink, creating a star mask following David Ault’s technique and reducing stars with Morph Trans
Downsize 50% and save as JPG