Comet Jacques (C/2014 E2), Aug 28th 2014

Contains: Comet

Technical card

Resolution: 3122x2230

Dates: Aug. 28, 2014

Frames: CLS-CCD: 39x45" ISO3200

Integration: 0.5 hours

Darks: ~12

Flats: ~12

Flat darks: ~12

Bias: ~50

Avg. Moon age: 2.17 days

Avg. Moon phase: 5.22%

Locations: Backyard, Hampton, VA, Hampton, VA, United States

Description

Comet Jacques (C/2014 E2) is a bright, long-period comet which I captured as it traveled rapidly among the stars of Cepheus on the morning of 2014-Aug-28. The total exposure length is nearly 30 minutes in duration using 45 second subframes taken between 5:04 - 6:36 UTC. Based on the comet's movement across the subframes, it was moving at approximately 9”/min, necessitating the short exposure length and high ISO to prevent streaking (though it still streaked).
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Processing Workflow (PixInsight)
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Pre-processing
1. Calibrate light frames using bias, darks, flats.
2. Make on integration where subframes registered to comet using a very small sigma high rejection value to remove the stars (CometAlignment).
3. Make another integration where subframes registered to stars using same rejection values as comet-aligned image to keep the background colors similar between the two images (StarAlignment).

Post-processing
1. Crop both images identically (DynamicCrop)
2. The comet-aligned image is brighter than the star-aligned image, so scale the comet-aligned channels linearly to match the star-aligned channel by dividing each channel by the ratio, computed for each channel: (PixelMath; cometAligned/starAligned).
3. Create star mask to transfer stars from star-aligned image (RangeSelection).
4. Transfer stars to comet-aligned image (PixelMath; using star mask)
5. Reduce background gradients (DynamicBackgroundExtraction).
6. Neutralize background (BackgroundNeutralization).
7. White balance (ColorCalibration).
8. Non-linear stretch (MaskedStretch; target background 0.2).
9. Set luminance coefficients to 0.33333 for RGB channels (RGBWorkingSpace).
10. Contrast curve (CurvesTransformation).
11. Comet color saturation (InterChannelCurves - reference channel: green, target channel: HSI saturation; star mask protecting stars).
12. Star color saturation (CurvesTransformation; star mask selecting stars).
13. Another contrast curve (CurvesTransformation).
14. Luminance and chrominance noise reduction (ACDNR w/ luminance mask).
15. Remove dark pixels (RemoveDarkPixel PixelMath process [Schwarz]).
16. Re-neutralize background by adjusting black point of each channel until median value of all channels in a small preview line up (HistogramTransformation).
17. Another contrast curve (CurvesTransformation).
18. More star color saturation (ColorSaturation; star mask selecting stars).
19. Brighten mid tones and lower black point to near 0.1 (HistogramTransformation).
20. Add color to star centers using method by Jerry Lodriguss (reference below).
20a. Clone image.
20b. Blur the clone (Convolution).
20c. Increase saturation (ColorSaturation).
20d. Blend 40% of blurred clone with 60% of original through star mask (PixelMath; w/ star mask).
21. Final crop to 5x7 aspect ratio (DynamicCrop).
22. ICCProfileTransformation to sRGB

References:
Manfred Schwarz galaxy tutorial:
http://www.astrophoto.at/PixInsight/
Recording and Enhancing Star Colors
http://www.astropix.com/HTML/J_DIGIT/STARCOLR.HTM

Comments

Author

Jason Tackett
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 Comet Jacques (C/2014 E2), Aug 28th 2014, Jason Tackett

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