I had a go with my data - ah the joy of posting small images on IIS is that the really egg-shaped stars are almost invisible! This is my un-modded EOS 60D, and 8 x 5 minutes at ISO800, with moderate light pollution and a setting 65% Moon. I thought I'd share roughly my processing to show how I didn't end up with a very blue Lagoon.
I initially automatically adjusted the histogram in PixInsight, which, rather interestingly
did overlap the red, green and blue curves (more fool me
), and it modified their intensity so that all the curves were as near as possible in both height and shape. But that gave an image with too much blue all over, so I adjusted the combined curves, reduced the blue and green curves separately just a bit, then as a last point I did a nonlinear stretch of curves on the red, concentrating on the highlights. [I blended in an HDR transform version to pick out some of the nebula details, but that's largely irrelevant here.]
It taught me a lot about the colours of this region, and my dumb eyes have probably stuffed it up and it'll appear green on everyone else's monitor
. My aim was to have something of a golden colour on the area around the globular to the lower left, to have the little banner of reflection nebulosity at the top left quite blue, and have the fringes of the main nebula as quite red (I think these come out as deeper red in most images, either due to more dust or less OIII). But boy is it subjective when you can't colour calibrate straightforwardly. There's certainly some blue in the middle, and I couldn't honestly say how much I feel should be there (more than I first thought?). And weird colours appear so easily when you fiddle with it.
I've attached 3 images - the first is the 'final' image, though the star shapes probably stop me from publishing it much bigger. The second is the basic stacked image with all channels stretched equally, showing a lovely orange light-polluted cast. The last image is the basic stack with channels stretched and matched by PixInsight so that red, green and blue overlap each other at the same intensity (it's a histogram gamma stretch and clips only).
Sometimes I wonder if black-and-white is the way to go...
