IC342 - Hidden Galaxy
Special thanks to M63 and Buras on the /r/astrophotography discord server for help on this image!
Equipment:
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Orion 8in F4.9 1000mm Newtonian Reflector
[li]Flocked / Primary mirror replaced due to turned-down-edge[/li]
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Skywatcher F4 Aplanatic Coma Corrector
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Astrodon I Series L, R, G, B broadband filters
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ASI183mm Pro cooled to -15C
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Celestron CGEM Mount
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Self tuned / hacks to get guiding stable include:
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Intentional offset polar alignment so dec always pulses in one direction
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Balance "west" heavy (rather than the recommended east) so that the ota "falls" onto the gear teeth rather than get "lifted"
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Factor Reset hand-controller daily (to prevent cgem from being possessed and forgetting where the meridian is on subsequent night)
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Dither in RA only
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Acquisition Details:
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Images captured using N.I.N.A
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Red: 32x2min
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Green: 31x2min
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Blue: 31x2min
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Lum: 62x2min
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All data was taken on a single night on 2019-11-24 with good seeing, but horrible guiding as I forgot to adequately balance the OTA west heavy. RMS bounced between 0.9"/px and 1.2"/px for most of the session.
The resulting image is a combination of the following steps:
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Inspected all 158 subs for bad images with Blink, discarding 2 (keeping 156)
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Calibrated all subs with their corresponding master flat and master dark
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Used subframe selector to weight all subs together using the following formula:
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(30*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin))
+ 20*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))
+ 15*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)
+ 20*(Stars-StarsMin)/(StarsMax-StarsMin))
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Selected the best sub from subframe and blink to use as a reference frame in stacking
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Created a super luminance by integrating all 156 frames together
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Integrated all Red frames together, Blue frames together and Green frames together to create masters for each color
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Cropped the stacking edges of the integrated masters
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Combined the Red, Green and Blue masters to create a color RGB image
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Superluminance Processing:
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Automatic Background Extractor
[li]Function degree 1 with normalization[/li]
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Independently produce a noise reduced image and a sharpened image
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Noise Reduction was done using TGV Denoise with a low contrast mask and an autostretched local support
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Deconvolution was done on a separate copy of the luminance with
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No deringing
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wavelet regularization with 5 layers and strong but reducing amounts/thresholds
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A starmask was created from the Noise Reduction copy to replace the stars with the origional superluminance, eliminating the ringing artifacts from deconvolution as similarly documented by /u/OkeWoke
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The noise reduced copy and the sharpened copy were combined using a luminance-based mask where the high-signal areas were filled in from the deconvolution copy and the low-signal areas were filled in from the noise reduction copy:
Decon*CombineMask+NR*~CombineMask
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Automatic Background Extraction with Function Degree 1 to remove gradient
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An additional round of MultiscaleMedianTransform was performed for additional noise reduction using a highly protective luminance mask
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A Histogram Stretch followed by Masked Stretch was used with no clipping and a background reference created from 5 preview windows and the Preview Aggregator script.
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The overall impact of the stars were reduced and star cores were shaped with two rounds of Morphological Transformation
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Morphological Selection
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Selection
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NumberOfIterations = 7
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Amount = 0.30
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SelectionPoint = 0.40
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A contours based Star Mask was used by
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Used Starnet++ to create a star mask
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Stretch, clip and convolve the stars only image
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Create a second copy of the stars only image and use morphological Dilation(maximum) to "grow" the size of the stars
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Subtract the image with the larger stars from the image with the normal-sized stars to create an image with "star donuts"
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RGB Processing:
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Automatic Background Extractor
[li]Function degree 1 with normalization[/li]
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Background Neutralization using 5 preview windows and the Preview Aggregator script as the background reference
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Color Calibration using Photometric Color Calibration using the Average Spiral Galaxy as the white reference
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Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support targetting luminance and chrominance
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Noise Reduction using MMT with a very protective luminance mask targetting luminance and chrominance
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Repair the saturated star cores with the HSV Repaired Separation script
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Arcsinh Stretch and Histogram Stretch to bring to non-linear
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SCNR Green on the background with a luminance mask
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Additional curves transformation to increase overall color saturation
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The super luminance and the RGB image were then combined using the Channel Combination tool in CIE L*A*B mode to apply the Super Luminance to the RGB image
Additional post processing steps:
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Curves Transformation to increase contrast
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HDR Multiscale Transformation using a (non-inverted) luminance mask
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4 layers
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B3 Spline(5)
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Targeting Lightness with Lightness Mask checked
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ACDNR to minimize remaining noise targetting luminance and chrominance
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Morphological Erosion (minimimum) with the larger star-star mask created previously to reduce overall star impact
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Additional stretch with Curves transformation tool
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Local Histogram Equalization to enhance fainter regions of the galaxy
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Inverted luminance mask applied
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Radius 128
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Contrast Limit 2.0
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Amount 0.300
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8-bit resolution
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Additional stretch with inverted luminance and Power of Inverted Pixels
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Order: 1.0
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Smoothing: 1.0
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Lightness Mask: Checked
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Additional HDR Multiscale Transformation using an inverted luminance mask
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Additional Local Histogram Equalization with previous settings
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Additional HDR Multiscale Transformation using an inverted luminance mask
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Final round of noise reduction with Multiscale Median Transformation and highly protective mask
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Final round of Curves with luminance mask
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Reduce reds
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Reduce green (slight)
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Lift blues (slight to match opposing green)
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Lift lightness (to match opposing reds)
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