IC342 Spiral Galaxy

IC342

Click image for full size version

January 18, 2014, published in SkyNews, July/August 2015 p. 36

SkyNews July/Aug 2015 p. 36This is IC342, a face-on spiral galaxy in Camelopardalis, in the far northern sky.  It is large in the sky, at about 2/3 the width of the moon.  But it is very faint.  I haven’t looked for it visually yet, but after seeing it in images I plan on hunting it down with my 20″ reflector.  It is a challenge both to observe and to image because it lies almost the plane of the galaxy, and is obscured by a lot of dust from the arms of our own Milky Way galaxy.  It lies about 11 million light years from us.  This image shows off many pinkish H-alpha regions dominated by glowing hydrogen gas, as well as lots of dark, dusty lanes in the arms of the galaxy.

Tekkies:
SBIG STL-11000M camera, Baader RGB filters, 10″ f/6.8 ASA astrograph, Paramount MX.  Guided with STL-11000’s external guider and 80 mm f/6 Stellar-Vue refractor.  Acquistion and guiding done using Maxim-DL.  Focusing with FocusMax.  Automation with CCDCommander.  Calibration, registration, integration and all processing in PixInsight.  Shot from my SkyShed in Guelph, Ontario. No moon, no clouds, average to good transparency and poor seeing.

20x10m R, G and B unbinned frames (total=10 hr).

RGB:
Creation and cleanup: R, G and B masters were cropped and combined to make an RGB image which was processed with DBE and ColourCalibration.

Deconvolution:  A star mask was made to use as a local deringing support. A copy of the image was stretched to use as a range mask. Deconvolution was applied (75 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 40 stars).

Stretching: HistogramTransformation was applied using autostretch settings from ScreenTransformation tool.

Synthetic Luminance:
Creation and cleanup: The cropped R,G and B masters were combined using the ImageIntegration tool (average, additive with scaling, noise evaluation, iterative K-sigma / biweight midvariance, no pixel rejection). DBE was applied to neutralize the background.

Deconvolution:  A star mask was made to use as a local deringing support. A copy of the image was stretched to use as a range mask. Deconvolution was applied (100 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 40 stars).

Stretching: HistogramTransformation was applied using autostretch settings from ScreenTransformation tool.

Combining SynthL with RGB:
The luminance channel of the RGB was extracted, processed and then added back into the RGB image as follows:
1. Extract luminance from the RGB image.
2. Apply LinearFit using the SynthL channel as a reference.
3. Use ChannelCombination in the Lab mode to replace the luminance of the RGB with the fitted luminance from step 2.
4. LRGBCombine was then used to make a SynthLRGB image.

Final Processing
Dynamic Range Adjustment and Stretching: HDRMultiscaleTransform was applied at 6 and 5 pixel scales, protecting bright stars with a mask. TGVDenoise was applied in RGB/K mode with default settings, followed by HistogramStretch.  A range mask was made that protected stars and background, and LocalHistogramEqualization was applied to the galaxy.  

Multiscale Processing:  A copy of the image was made and LinearMultiscaleTransform was applied to extract the first 4 wavelet layers (no residual).  This image (“SMALL”) was subtracted from the original image using PixelMath, to make an image containing only large scale structures (“LARGE”).  ColourSaturation was boosted on SMALL.  Curves was used on LARGE to increase contrast and colour saturation.  LARGE and SMALL were added together using PixelMath, with rescaling checked.

Final Steps: Morphological transformation (3×3, 6 iterations, strength 0.16) was applied using a star mask to protect background and galaxy.  Background colour saturation was reduced slightly.  ACDNR was applied using a mask to protect the galaxy and stars.

Image scale is about 1.1 arcsec per pixel for this camera / telescope combination.

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By | 2015-05-27T12:57:30+00:00 January 18th, 2015|Galaxies|2 Comments

About the Author:

An avid astrophotographer who has been hunting deep sky treasures with his camera and telescope for many years now. He enjoys sharing the amazing cosmos with others.

2 Comments

  1. Knox M. Henry January 19, 2015 at 7:52 am - Reply

    Wow! Spectacular! Thanks for a great astrophoto and informative write-up.

  2. Clark January 23, 2015 at 11:31 am - Reply

    Terrific shot Ron. Definitely worth a visual hunt!
    Thanks.

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