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Sh2-185/The Ghost of Cassiopeia - Your friendly Ghost :-)


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Well I hope you have your sunglasses on, well it is nearly Christmas, here's my version of Sh2-185 - The Ghost of Cassiopeia created in a HOS Pallet with RGB Stars.

So if you are a Vivian Westwood lover then this might appeal :-)

What a very strange object to process, when I first combined in SHO, i has a green nebula and no matter how much I tried it was proving very difficult to remove and let thing look natural. I tried in a number of alternative combinations and finally settled on this.

I found it wouldn't accept MLTNR noise reduction but would accept TVGNR, the RGB for the stars was fairly easy, thankfully.

10.3hours in total

GSO/Altair RC10"/F7.9, iOptron 120EC, Moravian G2-8300 MkII, Pegasus UPB, 2" Chroma Filters, Ultrastar Guide Camera, QHY OAG
More Info here: - https://www.astrobin.com/kmjr6y/

Here's the Bumf for those interested: -

IC63 (the bright, pointed object) and IC59 (the weaker object) are commonly called Sharpless 2-185 (Sh 2-185). Both are illuminated by the B0 IV star Gamma Cas. Both nebulae are near this ionizing star, but have very different visual appearances. IC63 can be described as a "comet cloud", refers to gamma cas and is narrower and sharper defined than IC59. Spectral measurements indicate that IC59 at 590K is slightly cooler and less dense than IC63 at 630K. Both are not separate nebulae, but part of a much larger nebulous region surrounding Gamma Cas. Both nebulae have spectroscopic mid-infrared detections of molecular hydrogen and polycyclic aromatic hydrocarbons (PAHs).

Experts are discussing whether the H-a signal we capture in our images is actually an emission from the nebula, or reflection of the H-alpha light emitted by Gamma Cas, which is scattered by the dust in IC59 and IC63. This light scattering and reflection is called ERE (extended red emission). Gamma Cas is the prototype of a B0 IV star that emits significant H-alpha light. As it is slightly cooler than a BO V star, it can only slightly ionize molecular hydrogen in its environment. Thus it is possible that the H-alpha we capture in our images is a mixture of both processes: direct H-a emission from ionization and ERE.


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Posted by: @Dmack1

I really like that John. The hazy nebulosity around the ghosts head gives it an otherworldly feel.

The green version does not really do it for me I'm  afraid- a bit like when they dye The Chicago River green for St Patrick's Day. Not a great look ? ? 

Totally agree David, that was just the combo version with no other processing and trying to remove the green and replace with gold is proving a problem, but I had a look earlier and I maybe able to desaturate and build the colour from, will see how it goes.


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Posted by: @Gina
Posted by: @Jkulin

This was it with a standard combination of SHO: -


That looks like green only to me John.  Seems you need to "up" the red and blue.

Thanks Gina, yes that is what I was playing with my it really is a mare, it is the first object that I have imaged where the Lum mask inverted make no difference at all. Very confusing.


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Posted by: @Hallingskies

I imaged this recently and found zip in Olll, though it is OK in Ha. It took lengthy binned exposures in RGB to catch the reflection nebula component, and even then it took some stretching which brought out the noise. Your version is quite smooth in that respect.

Thanks, did you experience similar problems?

There was some OIII but it was insignificant compared against the Ha and SII.


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Posted by: @Jkulin

Thanks you do well with that, what software did you use?

Thanks John. I used Pixinsight. Started off by applying Dynamic crop, followed by DBE. After that I applied Linear Fit, and tried to reduce the noise with MultiScaleLinearTransform, but that didn't work, so I colour calibrated, then stretched the image using a mixture of HistrogramTransformation, followed by MaskedStretch. Once stretched, I used MultiScaleMedianTransform on the noise, and that seemed to do the trick. There was a touch of magenta in the background that I removed by inverting the image, and applying SCNR. I reinverted the image and applied SCNR again. After that it was basically using color mask to play around with the colours. HDRMUltiscaleTransform was used to bring out a bit more detail, and LoacalHistogramEqualization. Finished with MorphologicalTransformation to reduce the stars a little.


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@AstronomyUkraine Thanks Brian, You did a couple of things that I have never done, colour mask and Morphological transformation.

My workflow is: -

WBPP or Manually combine, depending on which needs more attention if spanned over multiple night.
Dynamic Crop
I have used deconvolution, but most times it doesn't help much.
DBE on each Channel
Channel Combination
Colour Calibration or Photometric Colour Calibration or Autocolour
BGN if I am having issues but avoid as much as I can
Histogram Stretch, or Masked Stretch, but lately been using EZ Soft Stretch as that is kinder to the image.
BGN to tweak
Exponential Transformation
Curves and Histogram adjustments to correct and balance the colour
Sometimes UnsharpMask

I do similar with the RGB channel for the stars and then use convolution on the stars and then Pixel Maths to apply

All the way through I am using a variety of Masks and gentle use of SCNR.

Occasionally I will use other tools like Starnet, but that is generally my workflow.

This one has been my most difficult yet.

Looking at your workflow, I do wonder if the colour mask was what the trick that helped removed the green, I'll have a look at that and see if it works better.

Thanks once again.

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Spot the deliberate mistake????

I didn't stretch the Lum Mask, now reprocessing and hopefully will resolve...argh why does the most obvious thing evade you when you are tired.

It took a very helpful person on the PI forum to show me the errors of my ways ? ? ? 

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Posted by: @Jkulin

Looking at your workflow, I do wonder if the colour mask was what the trick that helped removed the green, I'll have a look at that and see if it works better.

Maybe the colour mask was the difference. I had another bash at it this afternoon, I think I lost a bit of detail in the first one. This latest version, I followed the exact same workflow, except, instead of a straight up SHO, I used a different formula in PixelMath.

Red Channel .6*SII+ .4*Ha

Green Channel .7*Ha + .3*OIII

Blue Channel OIII

I stretched it using STF, and dragging the icon onto HistogramTransformation. The image came out slightly yellow, but using ColourMask and adding a touch of red and green in curves, I ended up with this more hubble-like colour. I think I managed to extract a touch more detail too.



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Thanks Brian, I feel such a fool making a mistake like that, generally I don't start on any major colour changes until I have stretched, don't know why I did think of this, your has come out nice now, so at least I can work on mine, many Thanks.

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Thanks Brian, I've learnt a lot from Shawn at https://www.youtube.com/channel/UCIwWoJv_vi1US5zjyjRs_lg

He has a nice relaxed way to processing and lightvortex has been a blessing as well.

I thought over the last year I was starting to get grips with PI until I make a foolish schoolboy error.

I really appreciate your help.

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