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Pacman Nebula - collaboration in HaOiiiSiiRGB


gorann

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I have been struck how different the Pacman looks in RGB compared to NB. To me it looks like a red dust ball in RGB while it looks like an opening into another brighter world in NB (at least in Hubble palette). So here I explored how it may look like in a mix of RGB and NB data.

This is 15 hours of HaOiiiSii data collected by Steve and Lis Milne (aka Gnomus) merged with 3 hours of RGB data collected by me. After a lot fumbling with trying to mix different filters to different channels I ended up making a Hubble image of the NB data and mixed this 50:50 with the RGB image and then tweaked the colours so it resembles the RGB palette. Probably because there is so much data from different sources there was not much noise to deal with. There was more work in dealing with the stars since as usual these were considerably larger in RGB. My processing was done in PS.

Many thanks to the Milnes for allowing me to mess with their data.

The original versions with acquisition data are found here (both are with 5" apo refractors):
NB: http://www.astrobin.com/320125/B/
RGB: http://www.astrobin.com/274031/F/

 

Comments most welcome. Is it too bright, too red, wrong red, should there be more dust around (there is a bit more to bring out but I found it slightly distracting, or maybe not...)?

Cheers

Göran

IMG2370-98PS18 APF-RPS13rotatedPS2+HaSO PS22Sign.jpg

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5 hours ago, Petergoodhew said:

That looks pretty spectacular. Combining hubble with RGB is a bit uncoventional so I've no idea how it should look - Olly will probably throw a fit!

 

5 hours ago, sloz1664 said:

Superb images. The Pacman is a particular favourite of mine, I'm currently building a portfolio of nb / rgb images  and dare to hope they resemble your masterpieces :icon_biggrin:

Steve

Thank you both! Not sure Olly @ollypenrice has seen it or maybe it upset him so much he decided to look elsewhere. In any case, I think the colours are relatively close to RGB (i.e. rather natural). When I processed the Milne NB data, I initially put them together using the Hubble palette, and I then moved the colours towards my RGB image using a few rounds of "selective colour" in PS, before I merged the two images 50:50 and stared working on it. Here is the NB image I came up with (at this stage I had not worried about star coulour so disregard that) and my RGB image. The great contribution from the NB data is the details it brought to the comparatively featureless RGB image. NB is great at bringing in details and in this case it was data of particularly high quality - 15 hours of it. I only brought in 3 hours of data with my RGB image - so 83% of the credits should go to the Milnes! I also add the final composite image for comparison.

Gnomus Pacman HaSiiOii HubbleGN.jpg

IMG2370-98PS18 APF-RPS13sign-CR.jpg

IMG2370-98PS18 APF-RPS13rotatedPS2+HaSO PS26(star fix)Sign.jpg

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I have collated 13.3 hours of HaOiiiSii and 14.5 hours of RGB. Unfortunately my skies aren't as clean as yours. Also, my processing skills are, to say, dubious at present.

On the plus side. The subs can be stored until the day I can seriously understand the complex world of Pixinsight :icon_biggrin:

Steve

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I haven't commented simply because I haven't seen it till just now. No other reason.

I take a dim view of one person telling another what is, or is not, astrophotography and you won't find me doing that. I'm always happy to say what I do and don't do, and how and why. Would I do this? Well... honestly no, because I find the process incoherent. Colours have been falsely mapped (fine by me) and then given a graphics treatment to re-map them back to a subjective impression of natural colour and then merged with natural colour. By this time I'm lost - but I'm no genius so I've been lost many times before!

I may have misunderstood the process (and I have a lousy chest infection which isn't helping my mental clarity!!) but, in a nutshell, I don't get it. That's not your problem, it's mine.

For what it's worth I've imaged this object a couple of times at varying focal lengths and never felt I've done a good job.

Olly

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2 minutes ago, ollypenrice said:

I haven't commented simply because I haven't seen it till just now. No other reason.

I take a dim view of one person telling another what is, or is not, astrophotography and you won't find me doing that. I'm always happy to say what I do and don't do, and how and why. Would I do this? Well... honestly no, because I find the process incoherent. Colours have been falsely mapped (fine by me) and then given a graphics treatment to re-map them back to a subjective impression of natural colour and then merged with natural colour. By this time I'm lost - but I'm no genius so I've been lost many times before!

I may have misunderstood the process (and I have a lousy chest infection which isn't helping my mental clarity!!) but, in a nutshell, I don't get it. That's not your problem, it's mine.

For what it's worth I've imaged this object a couple of times at varying focal lengths and never felt I've done a good job.

Olly

I largely agree Olly. Merging so many colours and filters will likely make you drift off from what the object really looks like, but then NB imaging is extremely artificial when it comes to the colour presentation, where red is often made into green. So, then I thought it could be ok to do an exercise like this one, using the NB data to bring out more details and strive to keep the colours as close to the RGB data as possible, as you can see I have done if you compare the RGB image and final merged image. They are not that different in colours and there are at least no green stars there. Adding Ha to an RGB image will also take you away from a true representation of what the image would look like to our human eye color receptors.

Cheers

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3 minutes ago, gorann said:

I largely agree Olly. Merging so many colours and filters will likely make you drift off from what the object really looks like, but then NB imaging is extremely artificial when it comes to the colour presentation, where red is often made into green. So, then I thought it could be ok to do an exercise like this one, using the NB data to bring out more details and strive to keep the colours as close to the RGB data as possible, as you can see I have done if you compare the RGB image and final merged image. They are not that different in colours and there are at least no green stars there. Adding Ha to an RGB image will also take you away from a true representation of what the image would look like to our human eye color receptors.

Cheers

Of course it's OK! Who makes the rules? What rules? I think the key thing is to declare what you've done (as you did) and then let people look at the picture.

Regarding the addition of Ha to LRGB, my own view is this: I want the Ha-modified image to be as close as possible to the original in terms of colour. In terms of brightness, obviosly not. (Why shoot Ha if you don't want it to modify the image at all?) The whole point is to bring in the faint gasses just beyond our natural vision so that we can see they exist within the context of a largely natural colour image.

This makes for a fairly low, but non-zero, intervention on a natural colour image and, again, the intervention is declared.

Olly

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Here's a question...  On my own 3nm Ha data I can find no trace of the features I've ringed below. They're quite distinctive so, although they appear as red in this rendition, do you know which filter they come from in yours? I only know the Pacman in HaLRGB.

5a02c071d792e_GorannsPacman.thumb.JPG.32396adb718fb115dfda797af26b2c51.JPG

Olly

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Most of that signal is in the blue channel in my RGB image (first image below shows it in the blue channel after a few initial stretches) but I think I also see some of it in Milne's Oiii data (second image below). Even if it is in the blue channel there is so much red signal on top that it turns out as dark red. Of course you got me wondering if it could originate from some dust or condensation in my image train that got exaggerated after high pass filtering. However, after looking at some images on the net, I think I see the same structures also in other Pacman images, like this one by Jeff Signorelli:  http://www.skycrumbles.net/img_info/ngc281/ and in this one: https://news.sponli.com/en/page/14/

IMG2370-98PS9 BlueChannel.jpg

Milne 01_OIII_1200sx15PS3.jpg

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On 11/7/2017 at 20:45, ollypenrice said:

Of course it's OK! Who makes the rules? What rules? I think the key thing is to declare what you've done (as you did) and then let people look at the picture.

Regarding the addition of Ha to LRGB, my own view is this: I want the Ha-modified image to be as close as possible to the original in terms of colour. In terms of brightness, obviosly not. (Why shoot Ha if you don't want it to modify the image at all?) The whole point is to bring in the faint gasses just beyond our natural vision so that we can see they exist within the context of a largely natural colour image.

This makes for a fairly low, but non-zero, intervention on a natural colour image and, again, the intervention is declared.

Olly

Olly, I agree that there is nothing wrong with adding Ha to an RGB image. I guess even plain RGB imaging could by some be regarded artificial as it involves taking long exposures that bring so much more out of an object than our eyes would ever be able to detect.

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For me this is the classic dilemma in astrophotography.  Some are happy to produce 'pretty pictures'. Indeed I guess we all do in one form or another.  When NASA uses the Hubble palette they produce amazing images - but the mapping of filters to visible wavelengths makes no attempt to align them as close as possible to visible wavelengths.

As a qualified physicist my desire is to create images of the universe that are as close to what I imagine is reality, but accepting that we have no choice but to assign colours to non-visible wavelengths which in itself is artificial (what colour ARE X-rays?!)

But as Olly says it's ok to do anything you want but imho if you are posting publicly it's important to be clear and honest as to what you've done and what the image represents.

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2 minutes ago, Petergoodhew said:

For me this is the classic dilemma in astrophotography.  Some are happy to produce 'pretty pictures'. Indeed I guess we all do in one form or another.  When NASA uses the Hubble palette they produce amazing images - but the mapping of filters to visible wavelengths makes no attempt to align them as close as possible to visible wavelengths.

As a qualified physicist my desire is to create images of the universe that are as close to what I imagine is reality, but accepting that we have no choice but to assign colours to non-visible wavelengths which in itself is artificial (what colour ARE X-rays?!)

But as Olly says it's ok to do anything you want but imho if you are posting publicly it's important to be clear and honest as to what you've done and what the image represents.

Peter, I fully agree and I see so many AP images on various net sites that give no information on how they were put together. In this case I have just entertained myself with an experiment while waiting for clear skies and the moon to disappear, being curious to see if I could bridge the striking difference seen in NB and RGB images of the same objects (the RGB version often looking like a sphere while the NB one suggests a hole in the sky).

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