Author Topic: Arp 78 (NGC 772)_Galaxy in Aries  (Read 14663 times)

Offline sleshin

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Arp 78 (NGC 772)_Galaxy in Aries
« on: 2011 January 24 01:18:06 »
Hi All,

Haven't posted a new image in a while and thought this one was particularly interesting not only because it's an interesting galaxy with unusual structure but also because the processing was done almost entirely(95+%) in PI. Just some minor tweaks in PS which I find I use less and less. ;D

First the image which is an interesting unbarred spiral galaxy which is thought to be distorted from it's interaction with NGC 770, the largest of the three small galaxies to the upper right of Arp 78. The spiral arm in the outer region appears disturbed and probably represents a tidally driven structure. What appears to be a faint ? tidal stream is extending upwards towards the brightest of the three small galaxies(PGC 212884). I had 600 mins of Luminance data(some not used in the LRGB image because of higher FWHM values) and I wildly stretched and inverted this image to better show this feature.  Here is the LRGB image:

http://sleshin.startlogic.com/stargazergallery/main.php?g2_itemId=439&g2_imageViewsIndex=1

And here is the inverted Luminance:

http://sleshin.startlogic.com/stargazergallery/main.php?g2_itemId=451&g2_imageViewsIndex=1

In case there is anyone interested and to encourage feedback on the image and the work-flow, here is brief description of the work-flow I used:

1. Bias, Flat, and Dark Masters were created and then light frames were calibrated and registered. L,R,G,and B masters were made using the Linear Fit Rejection algorithm.
2. Created RGB Master with Channel Combine Module.
3. Dynamic Crop RGB and L Masters.
4. Prepared RGB master with DBE, Color Cal, non linear stretch with Histogram and Curves, Increased color sat with lum mask in place, and SCNR.
5. Prepared Lum master with DBE, Deconvolution with mask protecting everything except the galaxy, non linear stretch with Histogram to try to approximate the brightness of the CIE L* component of the RGB. Then ran the Linear Fit Tool to more precisely match the Lum master with the extracted CIE L* component as recently described by Juan.
6. Used these processed L and RGB masters to create the LRGB master using the LRGB combine tool.

The LRGB image was then further processed with:
1. ACDNR
2. Atrous Wavelets to first smooth the background and then very slightly sharpen the small structures in the galaxy. Appropriate masks were used here.
3. HDR.
4. Black point adjustments with Histogram Transform.

Those are the main steps. Feedback and comments always welcome.

Steve
Steve Leshin

Stargazer Observatory
Sedona, Arizona

Offline Emanuele

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #1 on: 2011 January 24 10:25:38 »
Who needs the Hubble when we have Steve....
 :surprised:

Offline sleshin

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #2 on: 2011 January 24 23:04:24 »
Thanks Emanuele, I think. ;D

Steve
Steve Leshin

Stargazer Observatory
Sedona, Arizona

Offline Silvercup

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #3 on: 2011 January 25 14:37:20 »
Excellent image. I agree with Emanuele, who needs HST.

Thanks for the workflow, it seems that Linear Fit Tool does a great job on LRGB conbination.

Best, Silvercup

Offline Harry page

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #4 on: 2011 January 25 19:14:44 »
Hi

Most excellent work  :D

I tried to find something to critasise , but I gave up  O:)

Thanks for letting us look  ;D

harry
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Offline sleshin

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #5 on: 2011 January 25 21:53:43 »
Thanks Silvercup and Harry. Your ind comments are sincerely appreciated.

Steve
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Stargazer Observatory
Sedona, Arizona

Offline JGMoreau

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #6 on: 2011 January 26 22:59:16 »
Another wonderful image Steve, i really like the way you process them.
Can you describe in more detail how you smooth the background ?
Thanks in advance,

Jean Guy
Quebec

Offline Nigel Ball

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #7 on: 2011 January 27 09:05:22 »
Stunning, absolutley stunning Steve  8)

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Offline sleshin

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #8 on: 2011 January 27 23:26:28 »
Thanks Nigel and Jean.

Jean, to "smooth" the background I use tools that work on controlling image noise which mostly resides in the low signal to noise background. The first tool that helps a lot is the LRGB combine module. After preparing the Luminance and RGB masters that will next be combined into the LRGB image, I generally find that there is a fair amount of noise particularly in the background and especially chrominance noise in the RGB image. The Chrominance Noise Reduction section of the LRGB combine tool does a very nice job of eliminating color noise especially in the background. I generally use the default values of 4/2 but on the Arp 78 image I used 2/1.

Next on the Arp image, I used ACDNR. The lightness mask was used to protect the galaxy and stars. I generally adjust the midtone and shadow sliders to optimize the mask. I then use trial and error to find good StdDev settings. For Arp 78 I used 1 for Lightness and 2 for Chrominance. This will do a good job smoothing the background but I usually find that there is a ring of noise around the stars because of the mask protection so I rerun ACDNR this time with the Lightness Mask off and an inverted star mask in place. Again, trial and error for the SD and other settings.

At this point if it appears that there is still a little noise I will sometimes use Atrous Wavelets for more smoothing. I did this for Arp 78. I removed("x") the 1st layer and enabled Noise reduction on layer 2 using default settings. This was applied with a mask that protected the galaxy only.

This generally results in a nice noise free background but sometimes there will still be a little scattered blotchy color in the background that doesn't belong there. If so I will remove it using the Color Saturation tool with a Luminance mask in place so only the background is effected.

That's a brief summary of my general approach. I am by no means an expert with PI and my work flow and process settings are changing and evolving as I get more experience and especially when one of the Jedi post tutorial like help. ;D I use lots of previews and the Real Time Preview window to try various settings before settling on which settings to use. I also like to step away for a while and come back later/tomorrow and see if I still like the result.

Hope that helps. Hopefully others will chime in with suggestions and/or their methods.

Steve
Steve Leshin

Stargazer Observatory
Sedona, Arizona

Offline JGMoreau

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #9 on: 2011 January 28 02:49:06 »
Thank you very much Steve.
Hope to do as well as you some day, your images are an inspiration.

Jean G Moreau

Offline Nocturnal

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #10 on: 2011 January 30 04:04:42 »
Awesome!
Best,

    Sander
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Offline sleshin

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Re: Arp 78 (NGC 772)_Galaxy in Aries
« Reply #11 on: 2011 January 31 21:12:26 »
Thanks, Sander.

Steve
Steve Leshin

Stargazer Observatory
Sedona, Arizona