M20 Trifid Nebula - LHaRGB with synthetic Lum

[Amaranthus]

A fairly long integration of the reflection (blue) and emission (red) nebula of M20, the fabulous 'Trifid Nebula'. This is a large HII region in Sagittarius, located about 5,200 light years away.

Full capture details and a high resolution version can be viewed here: http://www.astrobin.com/134243/

M20_Trifid_ED80TCF_SSG3_LHaRGB.jpg (193.77 KiB) Viewed 5927 times

The image was captured a few months ago from my Adelaide surburban backyard, using an Orion ED80T CT apo astrograph (at f/4.8), mounted on an AZ-EQ6. The CCD camera was an Orion StarShoot G3 mono, guided with PHD2 using a think OAG and an ASI120MM-S guide camera. It's taken me a while to dedicate the time required to do the processing!

The image is composed of the following:
Lum = 56 x 5 min
Ha = 18 x 10 min
R, G & B = 56 x 5 min for each channel
Total integration time of 21.7 hours.

I used the Ha data to really make the central emission region stand out above the background. I developed a synthetic luminance channel by blending an exposure-based weighting of the L, Ha, R, G and B luminances. All subs were unbinned.

Captured from late Aug to early Sept 2014, as weather permitted. Pre-processed with flats (light box), bad pixel map (based on 70 darks) and bias in Nebulosity. Aligned and Drizzled in DSS.

Post-processed in StarTools -- geez I love this software, it makes things so easy and 'natural'.

[admin]

That Ha adds a lot of punch for sure!
How did you process and combine color and luminance if I may ask?

[Amaranthus]

For chrominance, I first opened each channel separately, did a 'blind' wipe (but used temporary autodev to check result), then denoised (blind again), then saved the still linear data.

For luminance, I opened each channel (Lum, Ha, R, G, B) monochrome images separately, stretched/processed each until I was happy, and saved each file. Then I used Layers to build a synthetic L composite, blended according to exposure weighting (and downweighting the R, G & B so that they summed to the L).

I opened it all using LRGB, capped green and fired up the Colour module. The initial colours looked pretty good, but although I theoretically prefer Scientific, I ended up using Artistic Detailed because the former was just looking too garish. I used 50:50/CIEL, leaving Red/Blue as is, and downbiased Green to 1.12 - matching on the basis of a reference image I admired from a recently S&T Magazine, and tweaking the saturation until I was happy (about 170%). I then did a colour only Wipe, and fired up "Life" and used this to enhance the image further (including bringing out a little more of the blue of the intense part of the reflection nebula, and toning down the glare of the emission neb).

I'm happy to send some Logs if you're interested Ivo.

[admin]

I opened it all using LRGB, capped green and fired up the Colour module. The initial colours looked pretty good, but although I theoretically prefer Scientific, I ended up using Artistic Detailed because the former was just looking too garish. I used 50:50/CIEL, leaving Red/Blue as is, and downbiased Green to 1.12 - matching on the basis of a reference image I admired from a recently S&T Magazine, and tweaking the saturation until I was happy (about 170%). I then did a colour only Wipe, and fired up "Life" and used this to enhance the image further (including bringing out a little more of the blue of the intense part of the reflection nebula, and toning down the glare of the emission neb).

Thanks! I find it interesting to hear how people color calibrate in particular.