Comet C/2012 K1 (PanSTARRS), May 17th, 2014

Contains: Comet

Technical card

Resolution: 3448x2462

Dates: May 17, 2014

Frames: Baader Planetarium UV/IR Cut 2": 9x90" ISO1600

Integration: 0.2 hours

Darks: ~60

Flats: ~30

Bias: ~30

Avg. Moon age: 17.16 days

Avg. Moon phase: 93.64%

Locations: NASA Skywatchers dark site, New Kent, VA, United States

Description

Here is a belated image of Comet C/2012 K1 PanSTARRS taken on May 17th, 2014 as the comet was passing through Ursa Major. The bright orange star is Chi Ursae Majoris and the galaxy NGC 3877 is also visible in the upper left.

Initial processing of this image followed Harry Page’s comet alignment tutorial (reference below). Since the comet moved over the course of the exposures, I integrated two versions of the image - one aligned with the motion of the comet and one fixed on the stars. The stars were then pasted onto the comet-aligned image. I would like to sincerely thank Tomáš on the PixInsight forum for showing me how to match the backgrounds of these two images and combine them. I was quite stumped until he stepped in!

Revision B darkens the red channel slightly to balance the background in all the color channels. The difference is subtle.

-------------------------------------------------------------------------------------------
Processing Workflow (PixInsight)
-------------------------------------------------------------------------------------------

Pre-processing
1. Calibrate light frames using darks, bias, flats
2. Register star-aligned images (StarAlignment)
3. Register comet-aligned images (CometAlignment)
3. Integrate each set of images using Percentile rejection method since I only had 9 frames. (ImageIntegration)

Post-processing

Star-aligned image
1. Crop image to remove dithering borders (DynamicCrop)
2. Remove gradients (DynamicBackgroundExtraction; division)
3. Balance colors and stretch by setting midtones of R, G and B channels to median linear values of respective channels (Statistics, HistogramTransformation)
4. Stretch by setting midtone of RGB/K channel to 0.75 (HistogramTransformation)

Comet-aligned image
1. Crop image to remove dithering borders (DynamicCrop)
2. Match backgrounds between two images (LinearFit, star image as reference)
3. Remove gradients (DynamicBackgroundExtraction; division)
4. Balance colors and stretch by setting midtones of R, G and B channels to median linear values of respective channels (Statistics, HistogramTransformation)
5. Stretch by setting midtone of RGB/K channel to 0.75 (HistogramTransformation)
6. Clone background to remove remaining trailed stars (CloneStamp)

Combined star-aligned, comet-aligned image
1. Create mask selecting objects from the star-aligned image which will be pasted onto the comet-aligned image (RangeSelection; CloneStamp to remove comet;ATrousWavelets to smooth)
2. Paste objects from star-aligned image onto comet-aligned image (PixelMath; w/previously generated range mask applied to comet-aligned image)
3. Neutralize background (BackgroundNeutralization)
4. Darken background (CurvesTransformation)
5. Set luminance coefficients to 1.0 for RGB channels (RGBWorkingSpace)
6. Reduce green from background carefully (SCNR; luminance mask targeting background)
7. Increase color saturation (ColorSaturation; luminance mask targeting strong signal areas)
8. Reduce blue halos around stars (ColorSaturation; w/star mask)
9. Even background illumination (PixelMath [Wechselberger equation]; protect stars)
10. Increase contrast and darken background (CurvesTransformation with luminance mask protecting bright objects)
11. Reduce luminance noise (ACDNR)
12. Reduce chrominance noise (ACDNR)
13. Darken background to target median value of around 0.1 (CurvesTransformation)
14. Darken red channel to balance three color channels to 0.1 (HistogramTransformation)

References:
Harry Page’s comet alignment tutorial
http://www.harrysastroshed.com
Gerald Wechselberger’s PixInsight tutorials:
http://www.werbeagentur.org/oldwexi/PixInsight/PixInsight.html

Comments

Author

Jason Tackett
Like

Histogram

Comet C/2012 K1 (PanSTARRS), May 17th, 2014, Jason Tackett

Made possible by

O'Telescope BackyardEOS