NGC 6823 is an open cluster in Vulpecula that's embedded in a broad stretch of faint nebulousity (Sh 2-86). The dust structure on the upper side of the cluster is a small reflection nebula NGC 6820.

This image was captured in the second half of the night over four days in May 2020 after spending the first half of the night collecting data for a deep M81/M82 project. Since it's a pain to switch filters on my setup in the middle of the night, I decided to shoot this with just my CLS filter to help tame the light pollution in my Bortle 8 backyard. I'm happy with the fainter regions of nebulousity that I could capture, but I'm not 100% satisfied with my stars.

N.I.N.A. was used for all image acquisition. Stacking and processing was all done in PixInsight.

Processing Details

Overall this was a really fun target to process. The underlying data was high quality so the initial processing went really smoothly. I went through about 15 drafts of different workflows to experiment with ways to enhance the fainter regions. A really great learning opportunity for me!

Initial RGB Processing

1. DynamicCrop

2. DBE

3. Background Neutralization using an aggregate of several small background previews as a reference.

4. PhotometricColorCalibration

5. SCNR (Green / 0.6) to remove lingering green cast.

6. TGVDenoise with a low-contrast mask (Jon Rista method)

7. MMTDenoise with a high-attenuation mask (2x Chrominance & 2x CIE Y - Jon Rista Method)

8. Extracted synthetic L channel for futher processing

Synthetic L Processing

1. MaskedStretch + HistogramTransformation (x2) for stretching & black point

2. StarNet++ to create starless version

3. PixelMath to create a stars only version (L - Starless)

4. LocalHistogramEqualization (R=128 / Contrast=4 / Amount=0.1) to enhance faint regions

5. LocalHistogramEqualization (R=256 / Contrast=8 / Amount=0.03) to further enhance faint regions

6. Two rounds of MultiscaleLinearTransform for sharpening & noise reduction

7. PixelMath to re-add stars (Starless + StarsOnly)

RGB Processing (continued)

1. RepairedHSVSeparation + ChannelCombination to fix saturated star cores

2. MaskedStretch + HistogramTransformation for stretching

3. ChannelCombination to add the enhanced synthetic L channel

4. CurvesTransformation for color and contrast

5. Extract L component + LRGBCombination with Chominance Noise Reduction enabled to reduce lingering chroma noise

6. CurvesTransformation for tweaking blues slightly

7. SCNR (Green / 1.0) to remove final green cast from color tweaks

8. Final CurvesTransformation for tweaks

Big thanks to eigenVector and the r/astrophotography discord for processing advice!