M20 has been on my bucket list since before I started imaging. Before I moved I had no access to the southern sky and the time never quite seemed right on the Texas and SRO scopes. But, when an SRO teammate suggested M20 as a target I figured it was time to give it a try and, wow, am I ever glad we did! I had no idea how much detail was lurking around that nebula!

We decided to use all seven filters even though none of us had any idea how we were going to use them. Each filter turned out to be interesting with the OIII being perhaps the least interesting but the SII was a happy surprise. None of us had any idea just how much sulfur detail was hiding in there. But, I knew I wanted to present this in the natural RGB palette. The Triffid just wouldn't be the Triffid to me if it were in a psueocolor palette.That left the decision of how to make use of the narrowband data.Ultimately I decided to stretch the L and the three narrowband filters and then try some pixel math combinations to capture the important aspects of each. First I tried equal weighting all four filters but that gave up too much of the wispy reflection nebula details in the Lum. After a few iterations I settled on L + 0.75H + 0.5O + 0.5S (rescaling the result). This happened after each was stretched so that influenced how the weights interacted. Overall it worked pretty well. The Lum had all the bright reflection details but the H and S had a lot of faint details not so readily visible in the L.

Here are the details:

L:
blurXterminator
starXterminator (extracting unscreened stars)
GHS (GH, linear, GH)

H:
blurXterminator
starXterminator (extracting unscreened stars)
GHS (GH, linear, GH)
noiseXterminator

O:
blurXterminator
starXterminator
GHS (GH, linear, GH)
noiseXterminator
Histogram Transform (using GAME generated mask to bring down corner amp glow - needed because this was stretched harder)

S:
blurXterminator
starXterminator
GHS (GH, linear, GH)
noiseXterminator

combo L:
pixel math (L + 0.75H + 0.5O + ).5S - rescaled)
LHE
Curves (boos the low end to emphasize more wispiness)
MLT (mild sharpening)

rgb:
channel combination (RGB)
SPCC
blurXterminator
starXterminator (extracting unscreened stars)
GHS (GH, linear, GH)
noiseXterminator
LRGBCombination (adding combo L)
Histogram transformation (using GAME generated mask to de-emphasize star halo)
Dark Structure Enhance
pixel math in stars (screen)

stars (rgb)
GHS (GH)
pixel math in H stars (screen)
unsharp mask (very mild sharpening)

h stars:
GHS (GH)