Saturday, October 1, 2016

Dueling Galaxies at Cape Hatteras National Seashore

“Dueling Galaxies”, Cape Hatteras National Seashore, North Carolina, August 11th, 2016. Rokinon 16mm f/2.0 lens at f/2.8, 78 minute exposure (52 x 90 sec) at ISO1600, Vixen Polarie StarTracker.
On the night of the Perseid meteor shower peak, I drove three hours to Cape Hatteras National Seashore to enjoy the view and hopefully capture some meteors on camera. Indeed, I saw an amazing show that night! Fireballs blazed in all directions and I could see even several faint meteors continuously through until dawn, owing to the very dark skies (blue zone and a light pollution map). Despite my efforts, I did not capture any of the brilliant meteors I saw, but I am not disappointed because I spent much of my time just enjoying the show. With that said, here is what I did capture. “Dueling Galaxies” spans a region between the Milky Way and Andromeda Galaxy, not far from the meteor shower radiant. Being so close to the radiant, the meteors I caught were short and they fell along the path of the Milky Way which made them difficult to stand out in the photograph. The image is a composite of the images with meteors on the integrated, 78 minute exposure.

Processing Workflow
1. Initial crop (DynamicCrop).
2. Reduce gradient (DynamicBackgroundExtraction, subtract).
3. Neutralize background (BackgroundNeutralization).
4. Set white balance (ColorCalibration).
5. Reduce background noise (TGVDenoise with inverted luminance mask).
6. Mild non-linear stretch (HistogramTransformation, lower midtone slide by a modest amount).
7. Save as 16-bit tif.
8. Repeat the steps above with the five inividual images with meteors, adjusting thresholds as necessary. I also added chrominance noise reduction (MultiscaleMedianTransform to Chrominance) prior to the non-linear stretch. I ensured the median value of the individual meteor images matched that of the stacked master image.

9. Add individual meteors to main image by using masks that select only each meteor and setting their layer blend mode to Lighten with the background layer being the stacked image.
10. Apply contrast curve to each layer containing a meteor to brighten the meteor and darken the residual background that was not masked out (Curves adjustment layer).
11. Save flattened image as 16-bit tif. Open in new PSD file for following steps - I probably could have used a Smart Object rather than creating a whole new PSD file, but this seemed cleaner.
12. Non-linear stretch using screen-mask-invert (SMI) technique (Lodriguss technique modified by Scott Rosen, described on the Astro Imaging Channel).
12a. Duplicate background layer, blur using Dust and Scratches filter, radius 6.
12b. Select original background layer and paste as layer mask on blurred layer, invert.
12c. Set blurred layer blend mode to Screen.
12d. Reduce background brightness to that of the original image with a Levels adjustment layer.
13. Save as 16-bit tif.

14. Set luminance coefficients to 0.333333 for RGB channels (RGBWorkingSpace).
15. Reduce green cast (SCNR to green, 0.60 w/inverted luminance mask).
16. Increase color saturation (CurvesTransformation to S w/luminance mask).
17. Increase galaxy brightness (ExponentialTransformation, Power of Inverted Pixels order 0.8 w/luminance mask)
18. Sharpen (MultiscaleMedianTransform to lightness, +0.01, +0.02 to layers 3 and 4)
19. Increase color saturation (ColorSaturation to all colors except bluish-purple which was a color cast left over from so-so DBE, w/luminance mask)
20. Set blackpoint (HistogramTransformation, raise black point slider)

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