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Technical card

Imaging telescope or lens: Canon 50mm f/1.8

Imaging camera: Canon 550D

Mount: Vixen Polarie

Software: O'Telescope BackyardEOS

Accessory: DewBuster Dew Controller

Resolution: 4464x2976

Dates: June 8, 2016

Frames: 117x100" ISO1600

Integration: 3.2 hours

Darks: ~20

Flats: ~20

Bias: ~50

Avg. Moon age: 3.16 days

Avg. Moon phase: 10.86%

Astrometry.net job: 1136266

RA center: 249.584 degrees

DEC center: -22.397 degrees

Pixel scale: 17.193 arcsec/pixel

Orientation: 164.178 degrees

Field radius: 12.808 degrees

Locations: Cobb Branch, Drewryville, VA, United States

Description

Please check out my blog entry about this image where I describe the performance of my new Canon 50mm f/1.8 lens and Vixen Polarie mount, weighting methodology to maintain contrast with moonlight contamination, lessons learned during dynamic background extraction & color calibration and the processes I found most effective to emphasize dust in the Antares region!

https://jasontackett-astrophotography.blogspot.com/2016/07/antares-region-with-saturn-first-night.html

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Pre-Processing Workflow (PixInsight)
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1. Calibrate with flats, darks, bias. Debayer, register.
2. Weight subframes by inverse of median ADU value since the moon was present during the first hour. Weights ranged from 40-100% with the subframe having the highest median value given 40% weight. Formula taken from David Aults weighting spreadsheet (SubframeSelector).
3. Integrate using weights (ImageIntegration, Windsorized Sigma Clipping rejection).

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Processing Workflow (PixInsight)
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1. Initial crop to remove low SNR stacking artifacts along edges (Dynamic crop).
2. Remove gradients (DynamicBackgroundExtraction, subtract).
3. Neutralize background (BackgroundNeutralization using preview in upper right).
4. Set white balance (ColorCalibration, use entire image as reference w/structure detection enabled).
5. Set luminance coefficients to 0.333333 for RGB channels (RGBWorkingSpace).
6. Non-linear noise reduction (TGVDenoise with inverted luminance mask à la David Ault’s recipe, reference below)
7. Repair overexposed star cores for brightest star
7a. Execute Repaired HSV Separation script
7b. Combine H, S and V images through mask selecting only the brightest star cores (ChannelCombination)
8. Non-linear stretch, lower midtones slider (HistogramTransformation)
9. Reduce color saturation of reddish/magenta lens flare on bright stars.
9a. Generate mask selecting lens flare by extracting X and R channels (ChannelExtraction) then multiplying the two together with PixelMath, CloneStamp to remove the rest and ATrousWaveletTransform to remove tiny stars (deselect first two wavelet layers), curves transformation to increase mask aggressiveness.
9b. Reduce color saturation of red/magenta (ColorSaturation through flare mask X 2)
10. Increase color saturation (CurvesTransformation to S channel with luminance mask selecting foreground).
11. Brighten dust and image in general with Jerry Lodriguss’ SMI technique [Kantelberg reference below]
11a. Extract luminance, clip shadows & highlights (HistogramTransformation)
11b. Duplicate image and blur using ATrousWaveletTransform, deselecting first layer of 5 layers
11c. Combine duplicate with original image through inverted luminance mask using PixelMath expression: ~(~$T*~blurredDuplicate)
12. Reduce background brightness (GammaStretch R/K = 1.15 with inverted luminance mask)
13. Reduce color saturation of red/magenta lens flare (ColorSaturation through flare mask X 2)
14. Increase color saturation (CurvesTransformation to S channel through luminance mask)
15. Reduce red rims around small stars caused perhaps by lens refraction (?)
15a. Generate mask selecting small stars by subtracting R channel from G channel, ATrousWaveletTransform, deselecting residual detail to remove everything else.
15b. Reduce S channel with CurvesTransformation using small star mask.
16. Increase color saturation (CurvesTransformation to S channel through inverted luminance mask)
17. Reduce color saturation of red/magenta lens flare (ColorSaturation through flare mask X 2)
18. Reduce green cast (SCNR to green, amount 0.88 with inverted luminance mask)
19. Enhance dark dust lanes (DarkStructureEnhance script)
20. Increase contrast (LocalHistogramEqualization, kernal radius 150, contrast 2.0 amount 0.6 12-bit resolution with inverted luminance mask)
21. Increase color saturation (ColorSaturation through inverted luminance mask)
22. Reduce red rims around small stars (step 15 above X2)
23. Reduce purple lens flare around bright stars
23a. Create mask selecting purple lens flare with ColorMask, hue 300-350 degrees, CloneStamp out everything but larges lens flare.
23b. Reduce color saturation of purple lens flare (CurvesTransformation to S using mask above).
23c. Decrease brightness of purple lens flare since the last step made them whiter and brighter (CurvesTranformation to RGB/K using mask above). Repeat last two steps twice.
24. Balance background blackpoint using a small preview in upper right corner and adjusting blackpoints of R, G and B channels until median value of preview is the same.
25. Reduce sizes of small stars (MorphologicalTransformation, morphological selection, size 3, iterations 2, amount 0.55, selection 0.25; mask selecting small stars generated with RangeSelection and cloning out larger stars).
26. Increase contrast in dark lanes of Milky Way (“S” curve in CurvesTransformation to RGB/k using inverted extracted green channel as luminance mask)
27. Reduce chrominance noise (ACDNR to chrominance with built-in luminance mask).
28. Increase contrast in dark lanes of Milky Way (“S” curve in CurvesTransformation to RGB/k using inverted extracted green channel as luminance mask)
29. Sharpen (UnsharpMask, stdDev 2.0, amount 0.56 with luminance mask).
30. Final crop (DynamicCrop)

References:

“M42 PixInsight Tutorial” by David Ault for linear noise reduction
http://trappedphotons.com/blog/?p=642

“Exponential Transformations”, Rob Kantelberg
http://www.astro-imaging.com/Tutorial/PixInsight/EXP/en.htm#0201

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Antares region with Saturn, Jason Tackett

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