A long look at the catseye. Extreme dynamic range composition

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

A long look at the catseye. Extreme dynamic range composition

#1

Post by timh »

I have been trying to image - and just as challenging - to also process images of this object for about a year now. Starting from 'lucky imaging' and deconvolution to improve resolution of the catseye core - the project evolved into an attempt to capture the whole thing including the faint background nebulosity into a single image.

The image below is a compilation of 1) a simple RGB image of the stars 2) a 'lucky imaged' 1 and 10s exposure, deconvolved sharp image of the catseye core and 3) a narrow band OOH image of the background nebula. The processing trick was really to find a way to combine all three. 1) and 2) were easy but the hard part was finding a way to neatly and smoothly fade out the bright centre and diffraction spikes in the NB image so that it could be replaced with the high definition image of just the core -- accurately, without losing too much detail and making for a seamless transition. One of the great thing about PIxInsight is the PixMath tool which allows for flexible bespoke programming.

Imaging from 030822 to 110322 at Bortle 6 after moonset (or with the moon nearly set) except in the case of HA imaging for which it matters less (and anyway the moon was low in the south and the catseye in the north).

VX12 Orion Optics (UK) Newtonian (f = 1200mm, F4.0), SW parracor type coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm.

ZWO 2 inch R, G, B, L and UV/IR cut off filters, Optolong 7 nm HA filter, Astronomik 6 nm OIII filter

Imaging with ZWO AS1294 MM PRO mono camera at either 2.315um pixel (0.4 arcsec/ pixel) or 4.63 um (0.8 arcsec/ pixel) at -5 C.

Capture in live stacking in Sharpcap with FWHM and brightness filters applied. Master flats and darks in Sharpcap. Subframe selection and preprocessing in PI. Guiding (usually < 0.4 arcsec RMS) in PHD2.

1) The RGB image comprised, 194 x 10s green, 173 x 10s red and 166 x10s blue all at gain 124 and at 0.4 arcsec/ pixel. Processed as usual in PI using DBE background removal, MLT smoothing and histogram stretching.

2) The high resolution (FWHM ~ 1.3) catseye core image was 366 x 1s and 171 x 10s L frames combined in a high dynamic range composition, stretched using a masked stretch and then with this luminance applied to the RGB image so as to produce a colour RGB image.

3) The nebula NB HOO image comprised 71 x 3min HA and 71 x OIII exposures at 0.8 arcsec/ pixel and gain 151. These were linear fitted and combined in PI using pixmath as HOO at 100%, 0% and 10% HA into the R, G and B channels respectively.

The three images were then combined and manipulated using starmask, rangemask, morphology, curves and pixmath.

The catseye is such a fascinating object that it deserves some comment. I think ? the first nebula to which spectroscopy was applied (William Huggins) and in which he spotted the hitherto unknown OIII forbidden emissions -- at the time declaring it to be a new element 'nebularium' -- we now know of course to be from an excited spin state of O2+ ion. NGC6543 is thought to pulse out emissions of star stuff every 1500 years or so which form the bright ionized bubbles-like structures - the much fainter outer nebula comprises material that was released much earlier as the star left the main sequence. At the core is an extremely hot WR type white dwarf ionizing and energising N+ and O2+ to excited spin states and emitting red and blue-green from forbidden transitions. Hard X ray emissions providing evidence for a hidden binary companion star with a high energy acretion disc . It is likely therefore that the WR star is precessing as it orbit - which might partly account for the peculiar shape of the core nebula and the apparent multiple positions of the brownish unionized 'cap' material - possibly marking the axis of a former shell from an earlier pulse.


Tim
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CAT_Final image_affinity16_PX_big.jpg
CAT_Final image_affinity16_PX_big.jpg (221.83 KiB) Viewed 920 times
CAT_Final image_affinity16_PX.jpg
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Menno555
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Re: A long look at the catseye. Extreme dynamic range composition

#2

Post by Menno555 »

What to say Tim? This is just excellent. Great combination of the inner and outer parts and like usual, great writing!
Stellar job!! :D

Menno
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: A long look at the catseye. Extreme dynamic range composition

#3

Post by timh »

Thanks Menno! It was definitely a long haul project but rewarding and enjoyable because it provided a lot of learning along the way.

Will probably not image for a while now as I have decided to risk taking the mirror cell apart to see if I can fix some slight slippage within the clips as it flips --maybe unwise ..I hope not.

Tim
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: A long look at the catseye. Extreme dynamic range composition

#4

Post by timh »

It always seems to be that it is only a couple of weeks after posting an image that you clearly see everything that was wrong with it ! ? ! :-)

In the original image I had made processing errors in 1) colorizing the catseye luminance, 2) cleanly removing and adding RGB stars back into the overall NB image and 3) the catseye itself was not as sharp as it could have been in the way it was imaged and processed

So herewith improved versiions of the original image where the main improvement was to derive the catseye luminance from 737 x 2s exposures. 2s seemed a more optimal time to get good overall detail and sufficient SNR to apply deconvolution - then to stretch the image via histogram transformation and 12 bit core 16 local histogram equalisation in PI. As far as can tell by comparison with HST images deconvolution (400 interactions at 0.005 ringing protection) has not created obvious artifacts.

The other thing that I discovered was that it worked far better to use the LRGB function directly on the linear (rather than pre-stretched) RGB colour image to transfer the catseye luminance to get a more detailed colour image.

Anyway -- think that this now really is as far as I am ever going to get in getting fine detail into the catseye - with my particular equipment and location.

Tim
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CAT_finalPROJ3_RGBstars+pluscore_plusNB_curves_mlt_16bit_biggest.jpg
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CAT_finalPROJ3_RGBstars+pluscore_plusNB_curves_mlt_16bit_big.jpg
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Menno555
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Re: A long look at the catseye. Extreme dynamic range composition

#5

Post by Menno555 »

Hi Tim

The outer parts indeed are improved a lot.
The core though is too sharp, over-processed? It's not in "balance" now in the overall look. No criticism, just my personal view/taste :)
But overall a great showing of what is possible :D

Menno
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turfpit
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Re: A long look at the catseye. Extreme dynamic range composition

#6

Post by turfpit »

Good job Tim. I think you have squeezed every photon out of that. The long march to PixInsight mastery continues.

Dave
calan
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Re: A long look at the catseye. Extreme dynamic range composition

#7

Post by calan »

Wow. Excellent
timh
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Joined: Mon Aug 26, 2019 5:50 pm

Re: A long look at the catseye. Extreme dynamic range composition

#8

Post by timh »

Menno555 wrote: Wed Aug 31, 2022 9:51 am The outer parts indeed are improved a lot.
The core though is too sharp, over-processed? It's not in "balance" now in the overall look.
Hi Menno, Thanks. Yes it is a bit of a Frankenstein composition being 3 quite separate images that have been aligned to coincide. the difference in contrast and sharpness beween the centre and the outer is rather too obvious. It would probably be better to image the outer nebula for longer - 24h rather than 7 perhaps to bring it up to a similar level of SNR as the middle. A project to perfect some time in the future perhaps. Tim
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: A long look at the catseye. Extreme dynamic range composition

#9

Post by timh »

Thanks Dave and Calan,

On the Pixinsight learniing - it does indeed seem to be a never-ending path -- but with plenty of gems along the way -- plus the whole subject of deconvolution and in particular Richardson-Lucy deconvolution of images is quite deep --but also (as far as I can follow it) interesting.

Thinking of eventually trying to compile some learning on lucky imaging followed by deconvolution into a short " how to " tutorial piece along with links to some of the more accessible web commentary on how it works and when to apply it etc.

The best 'small' image I got to of just the catseye itself is probably the attached -- it was interesting to compare the final resolution of this deepsky lucky imaging/ Richardson-Lucy deconvolution with the sort of resolution you get - for example- in you Lunar surface images Dave obtained using lucky imaging and wavelet adjustment. I think that it is about the same. The main bright 'parallelogram' of the catseye is 18 x 21 arcsec - with features resolved at maybe ~ 1 arcsec which I think is about the same as being able to resolve a crater on the moon about a mile or so across? Others have done much better though - there is an amazing picture from a Polish astronomer on Astrobin of the catseye.
Tim
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CAT_Linear_PIXCOMB_3_1_RGBmono_plus_OSC_registered_to913x2s_LIN__LUMfromHDRC_171x10s_plus_913x2_LIN_HDRM_LHE_curves_MLTaffinity16bitPX_big.jpg
CAT_Linear_PIXCOMB_3_1_RGBmono_plus_OSC_registered_to913x2s_LIN__LUMfromHDRC_171x10s_plus_913x2_LIN_HDRM_LHE_curves_MLTaffinity16bitPX_big.jpg (19.42 KiB) Viewed 663 times
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