Processing result of M 81 & M 82 LRGB data from the Big Amateur Telescope (B.A.T.).

LRGB data contributed to this image by the following B.A.T. Discord members ...

Jarinn (Bortle class 2 sky):
RGB: 4.5 h per channel
L: 5.5 h

MrCrazyPhysicist (myself, Bortle class 4 sky, Schwentinental, Germany):
C 14 Edge HD + Hyperstar V2 + ZWO ASI 1600 MM Pro
L: 11.5 h

The Big Amateur Telescope (B.A.T.), initiated by Astrobiscuit, is a collaboration of amateur astronomers, who share their data in order to create deep, high-resolution images of Deep Sky objects and time-lapse animations of variable nebulae.

If you want to contribute data for this or other targets to the B.A.T. or help processing data, follow this link:

discord.gg/WK8qmrqcpq

After reading this comment https://www.astrobin.com/fqsrb1/B/#c890725  by @John Hayes , I replaced the photometric color calibration in my workflow by the proposed color calibration approach, which delivers more reasonable colors for M 81 & M 82.

Remaining issues: The color calibration is still not correct, a lot of purple and the spiral arms of the galaxies have a more cyan than dark blue tint. Purple colors seem to occur in areas with almost no color information. Color now only relies on the 4.5h/channel contributions by Jarinn, my 1h RGB C14 Hyperstar data was too noisy. Will try to capture more color data ...

Parts of the new workflow are based on the PixInsight Fundamental Videos for NGC 3486 (2021 version) by Adam Block.

Post-Processing:

PixInsight

RGB:
star alignment, NSG script, dynamic crop, dynamic background extraction, linear fit of red and green channels wrt blue channel, RGB channel combination, background neutralization, color calibration, masked stretch, increase color saturation using curves transformations, SCNR

L:
star alignment, NSG script, dynamic crop, dynamic background extraction, arithmetic average of the two L contributions using PixelMath, masked stretch to get a low contrast image of the IFN and galaxies,  manual stretch to get a hight contrast image of the spiral arms, arithmetic average of both stretches using PixelMath, luminance mask, HDRMT (number of layers: 6)

LRGB combination:
LRGB combination with chrominance noise reduction

LRGB processing:
luminance mask, color saturation enhancement, MMT, Softlight, range mask to protect the galaxies, enhancement of the IFN by curves transformations, desaturation of the sky background

Sharpening of L:
enhanced luminance sharpening using this video by VisibleDark based on this tutorial on chaoticnebula.com

Starless processing:
Star removal with StarNet2

Topaz Denoise AI:
Remove noise from starless image:
Low Light Mode On
Sharpen: 0
Remove Noise: 30

Finally, add stars to starless image using Pixelmath, SCNR, final contrast/color saturation enhancements with curves transformations

Adobe Lightroom:
Final contrast, histogram and color saturation tweaks