Saturday, October 1, 2016

Light in the East, from Cape Hatteras National Seashore

“Light in the East”, Cape Hatteras National Seashore, North Carolina, August 11th, 2016. Rokinon 16mm f/2.0 lens @ f/2.8, 6 x 90 sec at ISO1600 tracked with Vixen Polarie Star Tracker (sky) 2 x 180 sec at ISO1600 untracked (foreground).
Here is the second image from my trip to Cape Hatteras National Seashore for the Perseid meteor shower peak in August. I wanted to capture the glow I noticed in the sky facing east around 4:30 a.m. which was a good 45 minutes before astronomical twilight. At first I thought it was the zodiacal light, but I do not believe it is since the color is not whitish-blue and it is not quite diamond shaped. There is a faint whitish linear feature extending diagonally from the horizon toward the upper right that I suspect is the zodiacal light, but I’m not sure what to make of the light in the center. I wonder if this is just the glow of city lights along the eastern seaboard backscattering in the humid marine boundary layer. It was so humid at this location that I could see car lights driving down the highway a good five minutes before they passed by. In any case, I am pleased that I captured green and red airglow for the first time, attesting to the darkness of the Seashore. It is also cool how red the Orion Nebula looks on the horizon due to atmospheric extinction.

My goal for this photo was to capture un-trailed stars and a low-noise foreground (longer exposure) in a six panel panorama. Getting the foreground panorama and sky panorama to line up turned out to be a frustrating affair and masking to make a smooth transition along the horizon was very difficult due to the exposure differences. I was altogether unsuccessful. After more than five attempts, I decided to live with what I have here despite my dissatisfaction. Perhaps I will revisit this image once I gain more experience with processing these types of composites. For now though, I have a pile of other images waiting to be processed and this one has been holding up the lunch line. Time to move on!

Processing Workflow
(LR) Lightroom, (ICE) Microsoft Image Composite Editor, (PS) Photoshop CC
1. Raw conversion: enable lens profile corrections, remove chromatic aberration
2. Brighten shadows (Blacks +25)
3. Noise reduction (Luminance 15, Color 44)
4. Sharpening (Amount 43).
5. Export individual panels as sRGB 16-bit .tiffs

Image Composite Editor:
6. Stitch panels (ICE, stereographic projection)

7. Open sky and foregrounds panos as separate layers (sky on bottom, foreground on top).
8. Create layer mask to select only foreground on foreground layer.
9. Align sky and foreground using warp tool (was a total pain and the result is imperfect).
10. Increase contrast of sky (Brightness/Contrast +21)
11. Increase contrast of sky (Curves)
12. Increase contrast of foreground (Curves)
13. Increase foreground brightness (Exposure +0.32)
14. Save flattened image as .tif
15. Rotate flattened image to level horizon.
16. Save as .tif

17. Noise reduction in foreground using adjustment brush (Noise +71, Sharpness +33)
18. Increase midtone contrast in foreground using adjustment brush (Clarity +20)
19. Increase contrast and darken sky using adjustment brush (Contrast +40, Blacks -20)
20. Final crop to 8 x 10 aspect ratio
21. Resample to 2400 pixels

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)