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  #1  
Old 19-03-2017, 08:31 AM
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MLParkinson (Murray)
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Four-panel mosaic of the Lagoon Nebula region

This is a four-panel mosaic of the Lagoon Nebula region imaged using 12-nm filters centered on the spectral lines of Hydrogen alpha, Sulfur II and Oxygen III. All the data were recorded in the outer suburbs of Sydney, Australia. It took me 1 million years to merge all of the panels because of light pollution gradients.

https://flic.kr/p/SR6n4a

https://flic.kr/p/RKTRv5

https://flic.kr/p/Ssynqf

Technical details:

Televue Nagler Petzval 127is at f/4.2, Astronomik 12-nm SII, Ha and OIII filters, QSI683wsg camera cooled to -20 Celsius. All sub-frames at 2x2 binning.

I would recommend using 1x1 binning whenever possible. However, I used 2x2 binning to record about 350 sub-frames at 10 minutes each to create a four-panel mosaic. 2x2 binning helped to reduce the total integration time.
Attached Thumbnails
Click for full-size image (2016_07_04_M8_M20_HaHaGOIII.jpg)
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Click for full-size image (2016_07_04_M8_M20_HaHaSIIOIII.jpg)
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Click for full-size image (2016_07_04_M8_M20_HaSIIGOIII.jpg)
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  #2  
Old 19-03-2017, 08:43 AM
Placidus (Mike and Trish)
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Hi, Murray,

The composition, depth, sharpness, and contrast are great.

Don't suppose we could talk you into a straight Hubble R=SII, G=Ha, B=OIII rendition? Not for aesthetic reasons, but because it is familiar and helps me think about what I'm looking at.

Best,
Mike
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  #3  
Old 19-03-2017, 02:29 PM
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Very dramatic, Murray! I like the first colour scheme best.
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  #4  
Old 20-03-2017, 05:48 AM
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Nice work Murray. I also like the first colour version the best. You have mastered that golden colour scheme with some blues and its quite aesthetic.

Greg.
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  #5  
Old 20-03-2017, 06:53 PM
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Quote:
Originally Posted by Placidus View Post

Don't suppose we could talk you into a straight Hubble R=SII, G=Ha, B=OIII rendition?

Best, Mike
Thank you for your positive feedback Mike.

You would like to see a “straight” Hubble rendition? Is there any such thing?

To me, the Hubble palette is a challenging exercise in colour manipulation. In the process, much of the useful H alpha depth and contrast is suppressed in favour of the low depth and contrast of the sulphur channel. Andy01 has a knack for building exceptional Hubble palette images. Not me. Perhaps it is easy when you have the right tools, and you know how! I’ve still got a lot to learn!

The H alpha channel has tremendous bit depth, and the sulphur channel little, even when I expose on the sulphur channel for 40 minutes. If I construct a straight Hubble palette image the result will be garish green because the H alpha green channel dominates the palette, with the sulphur red channel far too weak to prevail in the image.

Perhaps one of the leading photographers in this forum might write and post an easy to understand tutorial on how to achieve a pleasing Hubble palette result using PI.

Best wishes, Murray
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  #6  
Old 20-03-2017, 07:00 PM
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Thanks Greg and Rick. Several other members of this forum have expressed a preference for the first colour palette. I can recall one member implied he thought it was an Australian palette, like our sun burnt country. I should take good advice and concentrate on the sun burnt country palette. If people like it, they like it, and I should respect that. Best wishes, Murray
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  #7  
Old 21-03-2017, 07:58 AM
Placidus (Mike and Trish)
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Quote:
Originally Posted by MLParkinson View Post
Thank you for your positive feedback Mike.

You would like to see a “straight” Hubble rendition? Is there any such thing?

To me, the Hubble palette is a challenging exercise in colour manipulation. In the process, much of the useful H alpha depth and contrast is suppressed in favour of the low depth and contrast of the sulphur channel. Andy01 has a knack for building exceptional Hubble palette images. Not me. Perhaps it is easy when you have the right tools, and you know how! I’ve still got a lot to learn!

The H alpha channel has tremendous bit depth, and the sulphur channel little, even when I expose on the sulphur channel for 40 minutes. If I construct a straight Hubble palette image the result will be garish green because the H alpha green channel dominates the palette, with the sulphur red channel far too weak to prevail in the image.

Perhaps one of the leading photographers in this forum might write and post an easy to understand tutorial on how to achieve a pleasing Hubble palette result using PI.

Best wishes, Murray

Hi, Murray,

We wouldn't call ourselves narrowband experts, but we think we're on our green P-plates. Our approach: Take enough SII so that after background subtraction you have roughly equal total photon counts in all channels. Then the problem completely goes away, and the choice of palette is decoupled from the relative intensities.

The universal problem as you elegantly point out is that sulphur emission for most objects is typically say five, ten or twenty times weaker than the H-alpha emission. That means that if one only collects enough data to get the H-alpha channel looking good, then one hasn't really done a three channel image. It's only a 2.2, 2.1 or 2.05 channel image. You can't get round that shortage of information by any choice of colour, only by getting more information!

We tend to throw a complete night - say 6 or 8 hours - just at the sulphur channel, sometimes a couple nights say 14 hours - in order to get an adequate amount of information for a true three-channel image. Another approach, if you are normally over-sampled, is to use 2x2 binning (with dithering) on the sulphur channel, in which case you get four times as many photons per pixel in the SII channel, and you can get enough info in the SII channel in a couple hours or so.

So once you have enough SII data - either by throwing hours at it or by 2x2 binning, the next step in our mind, regardless of what mapping you have chosen, is to carefully set the zero point for each channel to the foothill of the histogram, so that black is black, but there is no information loss. The final step is to set the white point so that the average value for each channel is the same. No channel outweighs the other. For example, if (after subtracting moonlight and sky glow) there is twenty times as much H-alpha up there as SII, you make the SII channel twenty times brighter, and now they are balanced. If there is 5 times as much H-alpha up there as OIII, you make the OIII channel 5 times brighter, and it now balances both the other two. All three channels will have the same average brightness.

It is very important to notice that if you are using 32 bit processing (which you should) you have lost no information in the H-alpha channel by making the SII channel brighter. A corollary is that no harm comes from having even more information than you need in the H-alpha channel. You can never have too much.

The approach I've outlined means the image isn't ghastly green (like our early stuff used to be), but it doesn't have to be riotous red, or billious blue, or magenta or cyan either, but shows the differences between regions. There is even some advantage to using a modified version of this 'colour agnostic' approach on straight RGB galaxies, because it means you can up the saturation quite strongly, to show the differences between regions - core and spiral arms for example - without the galaxy as a whole becoming all the one colour.

Confession: For the Lagoon end of Bigfoot, the approach I've outlined works really well. For the Big Toe end, there is so little SII that we gave up and did a two channel image.

Very best,
Mike

Last edited by Placidus; 21-03-2017 at 08:13 AM.
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  #8  
Old 21-03-2017, 06:45 PM
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Mike, your post is a pleasure to read. I am printing a hard copy for future reference. I will definitely attempt to master your suggested workflow. I think that I understand everything you say. Hopefully all I needed was an expert like you to shift my thinking. It might take me a long time before I find a suitable day to try your workflow, but I will post the result when I do. Thanks again for so much clarity.
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  #9  
Old 23-03-2017, 05:07 PM
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Hi Murray, Nice work on the image - well composed and a good result from your LP location.

Leaving colour palette aside for a moment, there's something weird going on the core of your M8 - it looks overly smoothed and lacks detail and contrast.
This is odd because you have spectacular detail in all the dark whispy areas between the trio, which is awesome. May be worth revisiting processing with a mask or two over the core area.

As to colour palatte issues, Mike (Placidus) has posted a very good insight into the inherent problems with NB imaging and the lack of signal in certain wavelengths.

There are many ways around this, but as Mike says, the best result is to gather bucketloads more S2 data in this case as the Ha can easily overpower the others.
Some targets eg: NGC 6357 aka "The Lobster" are very weak in O3.

Quote:
Originally Posted by MLParkinson View Post
Andy01 has a knack for building exceptional Hubble palette images. Not me. Perhaps it is easy when you have the right tools, and you know how! I’ve still got a lot to learn!
Thanks for the nice feedback - for what it's worth, I use a variation of this method in PS https://astrodonimaging.com/tutorials/ (Tutorial 9)
Followed by selective colour to taste - http://bf-astro.com/hubblep.htm.
I'm not a fan of "true Hubble" green dominated images, and will happily push established boundaries in pursuit of aesthetics - but each to their own.
And as we're all still learning, keep going and keep 'em coming :
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  #10  
Old 24-03-2017, 10:42 PM
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Great fov in this image Murray. Yes the first image is my favourite too, but yes far more colour range should be possible.

Do you use the SHO-AIP script in PI? I find it crucial and intuitive to balance out the different filters. Tweak the percentage sliders over and over again until you go mad, well until the result is balanced at least, it achieves similar results to the Astrodome tutes that Andy posted. Happy to video an example if you want. Also, use Linear Fit to ensure each NB image is equalised.

Even after all the pi work, you still need to rework the balances in PS, using selective colour and any other colour balancing tools. Haha, then I usually Goto Lightroom after that, it has very impressive and easy to use colour balancing sliders.

Have fun experimenting and achieving new looks.
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Old 24-03-2017, 10:57 PM
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Dble post!
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  #12  
Old 24-03-2017, 11:30 PM
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# 1 looks the goods for colour to me.
But: it's over binned.
I doubt you'll sort the core out in software.
M8's right there over head and bright.
Bin 2x2 SII for double the exposure time on dim SII objects.
But Brilliant effort joining it up. My attempts at that are pathetic.
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  #13  
Old 25-03-2017, 10:26 AM
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Quote:
Originally Posted by Andy01 View Post
Thanks for the nice feedback - for what it's worth, I use a variation of this method in PS https://astrodonimaging.com/tutorials/ (Tutorial 9)
Followed by selective colour to taste - http://bf-astro.com/hubblep.htm. :
Quote:
Originally Posted by SimmoW View Post
Do you use the SHO-AIP script in PI? I find it crucial and intuitive to balance out the different filters. Tweak the percentage sliders over and over again until you go mad, well until the result is balanced at least, it achieves similar results to the Astrodome tutes that Andy posted. Happy to video an example if you want. Also, use Linear Fit to ensure each NB image is equalised.
Thank you very much Andy, Simon and Robin. I am now overwhelmed with new workflow suggestions. I am very grateful. It is important to break bad habits, and shift one’s thinking, to produce better images.

Now all I need is a gigantic East Coast Low to dump mountains of rain, making it impossible for me to leave my house. Then I will be forced into drinking gallons of coffee re-processing the raw data all weekend long.
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  #14  
Old 03-06-2017, 01:40 PM
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Four-panel mosaic of the Lagoon Nebula region: Remixed

Well, it is long time since my last post, as it usually is. A number of people provided constructive suggestions on how I might improve my work flow for the Lagoon Nebula mosaic. I want to assure you that I spent a lot of time thinking about what you said, and I have tried my best to achieve a more pleasing result. Here are the results of my latest attempt. I have attached thumbnails of the new and old [H alpha, Green, OIII] images for comparison. I like to think that the new one is an improvement, though perhaps it is only different. I am still struggling with the Hubble palette, but I like to think that I am making progress, learning how to manipulate the colours using more sophisticated tools.

The new full resolution images are here:

https://flic.kr/p/VaU7tw

Thank you for your good advice.
Attached Thumbnails
Click for full-size image (2016_07_04_M8_M20_HaHaGOIII.jpg)
197.4 KB24 views
Click for full-size image (2016_07_04_M8_M20_HaSIIHaOIII.jpg)
199.0 KB25 views
Click for full-size image (2016_07_04_M8_M20_Mosaic_Ha.jpg)
194.5 KB17 views
Click for full-size image (2016_07_04_M8_M20_HaHaGOIII_Old.jpg)
199.7 KB20 views
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Old 04-06-2017, 08:35 AM
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Even more dramatic, Murray!
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Old 07-06-2017, 07:58 PM
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The Rick S ColorMask script

Thanks Rick. I downloaded and installed the ColorMask script developed by Rick S. It is very easy to use and I think it has enormous potential for enhancing the colours in astronomical images. My hunch is that I will end up using it for RGB and LRGB images, as well as narrow band images.

Most of the elites on this forum have probably already scrolled down to “Free Download: Extra material”. I am catching up, slowly.

http://www.springer.com/gp/book/9783319256801

Best wishes, Murray
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  #17  
Old 08-06-2017, 10:07 AM
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Hi Murray,

Glad you like the script. I used to do some final colour tweaks in PS but now I can do it all in PI. As you say, it's good for RGB colour as well as narrowband.

Cheers,
Rick.
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