This is a 2-panel mosaic of Andromeda which I took from 3 different locations in two states and it is one of my most extensive projects to date. I started this from a local Bortle 2 Star Party which was hastily organized at the end of August where I captured Luminance, captured the RGB and Ha (7nm) from my Bortle 4 home, and finally ended the project with another night of Luminance at the OkieTex Star Party in late September. My primary motivation in shooting this as a mosaic was avoidance of yet another generic diagonal M31 image - I think giving the galaxy some framing on all sides just looks better.

Challenges associated with this project can be found by following the attached link to my website Astronewton.com, but I will say here that, as with every other new imaging project, I learned a lot. Unfortunately my experimentation in new techniques led to an extensive delay between image capture and releasing this final image.

Pre-Processing:
- Darks & Flats Calibration, Cosmic Correction
- Subframe Selection & Local Normalization
- Star Align of all channels to the best Ha frame of each panel
- 2x Drizzle Integration

Housekeeping:
- Common Crop per panel
- Combined into Mosaic per Light Vortex Tutorials page
- Second crop
- DBE for each channel
- RGB Combine
- Photometric Color Calibration
- HDR combine of 240s, 120s into Master Light channel (also used Ha image for finer core detail)



Ha+R & L:
- Copied Ha image, ran STF stretch
- Starnet to remove stars, creation of Star Mask
- Erosion and removal of stars on Linear Ha image
- Isolation of Ha from Red Continuum, addition to Red channel using PixelMath
- Background Neutralization of HaRGB
- Same process for adding isolated Hydrogen to Luminance master

Main Processing:
- HSV Repair on HaRGB
- TGVD, MMT noise reduction (Jon Rista method) on HaRGB, L
- SCNR for removing excessive green

Non-Linear:
- ArcSinH for L, HaRGB
- Histogram Transformation to match Histogram peaks
- LRGB Combine
Fine Tuning, or quite literally about 100 varying Curves, HDRMT, Histogram changes to correct:
- Addition of HDR detail into the brighter core using dust lane mask to preserve core luminosity)
- Masked brightening of larger pixel scale dust (per Inside PixInsight book)
- Color correction to "cool" Blue tones, turn pinkish Ha highlights more Red, and careful increase of color
- Finally, MT for star reduction



Notes for 2022 Reprocess:
 - Hα blended to both Red and Blue in a 1.0:0.3 ratio reflecting Balmer series emission lines