I tried searching the forum for "H-II" but gave up looking after the first 30 hits, or so. So, if this topic has already been covered, please point me to the appropriate thread.
With the popularity of OSC cameras has come the advent of dual narrowband filters to make good use of their RGB capabilities for emission nebulae. The H-I+O-III filter would suit generating HOO palette images, and adding a S-II+H-II filter allows one to include SHO palette processing. However, this latter processing would use just the S-II data in the red channel, and completely ignore the very nice imaging resulting from the H-II regions in the G & B channels. So, I am asking: how should/could I use the H-II emission data?, as it would be a waste not to use it, and there is scientific interest in H-II emission regions.
An obvious answer would be to combine the H-II and H-I data into just the red channel. However, it occurs to me (perhaps wrongly) that while H-II emissions are probably generated in the same areas as H-I emissions, the reverse is probably not true. That is, the H-I emission regions are not all energized sufficiently to produce H-II emission, so that the H-II emissions are from specific regions within the H-I emissions, and to my mind, are worth accentuating in some way. What say you, and how should I do this as all 3 channels are already assigned? Would a light red for H-I and a dark red for H-II achieve an acceptable result, and how might I do this?
Paul.
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Pixel math is your friend  . Create your own G and B channels by combining the O3 and H2 data. Maybe something for green like O3*0.9 + H2*0.1 and blue something like O3*0.8 + H2*0.2. Fiddle around with the math until you get a result you like. Note, I've never used an H2 filter, so the pixel math formulae I provided are just examples, not any kind of definitive statement of ratios to use in your combination.
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When it comes to false color it doesn't matter, you can combine it in whatever way pleases you. For true color you would want Hα as Red and Hß as Blue. With just an Hα filter you could potentially blend the Hα into Red and then a little into the Blue channel using a Luminance mask to affect only the bright areas under the assumption that brighter = higher energy = more probable presence of energies required to generate the Hß line. It still comes down to guesswork.
As you mentioned only OSC and not Mono I assume this is what you use, and in that case you could probably make use of the Radian Triad Quadband filter. Its sold by OPT (or was, more accurately), so I am unsure how easy one would be to obtain. But if you find one, it passes Hα, Hß, OIII, and SII all at once with a pretty reasonable 4-5nm, which would enable a OSC camera to capture all of those bands in their natural colors. The only downside would be isolating Hα from SII would be impossible, and OIII from Hß would have similar problems - but this is only a problem for false color, for true color its an advantage.
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Thank you, Jonny and Brent, for your interesting inputs. As I implied, I am using OSC cameras with the two filters I mentioned (Antlia ALP-T) which now puts me in a richer data set than the usual H-I, S-II, O-III using mono cameras. Something like the Radian Triad Quadband filter you suggest, Brent, would be a step back from this because, as you say, it would be next to impossible to separate out the contributions from the 4 emissions. It would probably make life simpler for OSC imaging, though, but since I've got the data, I would like to use it to advantage.
I guess it's a matter of taste how a 4th emission is incorporated into a false-colour image palette like SHO. I think I will be fiddling with a tool like NB Color Mapper, which takes the pain out of PixelMath. I suppose I was wondering whether there is some agreement on a 4-emission line palette, but I guess it will be a matter of a lot of trialing by us photographers to work out what works well, with the option of changing to suit the subject/taste. There may be a case here for using a colour/colours that most seem to shy away from: green & magenta to name two. There's also the degree of overlap to consider. If I wanted the H-II to make its presence obvious, it might mean dialling back the H-I signal. Ah! Lot's of fiddling to try out!
I'd like to hear what anyone has done wrt a 4-emission line palette. What has worked, and what hasn't?
Paul.
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From what I read, H-I and H-II refer to atomic hydrogen and ionized hydrogen.
Emission lines and filters are Ha (656) and Hb (486), which are red and blue (more blue than O-III).
That's how you'd mix them into an image.
I'm no physicist, but H-II has no electrons so you're camera wouldn't see it.
I suppose.
Emits in radio and infrared, apparently.
Ha and Hb would both come from H-I.
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Thank you, Mijo. It's the H+ emission at 486.1nm that I am recording through my Antlia ALP-T S-II+H-II filter. Apart from the S-II line at 672.4nm, all other visible and near UV & IR light are blocked. The H+ ion may well emit radiation at other, non-visible wavelengths, but these are not of interest to us ordinary astrophotographers.
What I get with this filter are images relating to the S-II emissions in the red channel, and H-II emissions in both the green and blue channels. It's what I should do with the G & B channel data that I'm enquiring about and interested in what others are doing as this is a 4th emission line to work with (together with H-I, O-III & S-II). As dual Sb+Hb filters are relatively new for OSC cameras, this is probably early days for this topic. It's likely to be interesting to see how others tackle this issue.
Paul.
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H+ it's for chemistry identification, we should use the HI (or H-I) terminology as it customary in astronomy for ionized hydrogen. The HI ion does not emit anything as it is a free proton (at least in its base state). So stop referring to it. The Balmer sequence of emission lines in the visible spectrum for H-II is the following:
name : H-alpha H-beta H-gamma H-delta
wavelength: 656.279 486.135 434.0472 410.1734
What you do with it is to read it from the B channel of an OSC sensor and stick it to the same B channel extracted for an OSC sensor when recording OIII dual line emission and use it in an RGB image. Depending on the sensor you might want to subtract H-alpha response into the same channel and/or continuum response, if you feel like nit-picking.
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Thanks, Andrea, for your input. Yes, I'm aware of the distinction between the Chemical and Spectral fields, but being a research chemist in another life it's easy for me to gravitate to the chemical side. But, you are right, we are in the Spectral field here, and should use its nomenclature. It should save confusion. So, my apologies.
Am I wrong in my understanding that the reasoning behind the false-colour "Hubble Palette" is to bring out the details of each of the H-I, S-II, and O-III emissions from a nebula, especially where there is little colour distinction between H-I and S-II? What I was asking with this post is whether anyone has given consideration to accommodating a 4th emission, in particular H-II emissions. (My filter is a 5nm band pass, so the H-gamma and H-delta would not be passed.) At this point, I'm not all that interested in "true" colour rendition but in giving some distinction between the 4 emissions. I hope this makes some sense, and clears away any confusion.
Paul.
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Unless you are a very very very very very rare female human being your color vision is restricted to trichromacy hence you can't use the 4 independent color channels that Hbeta, OIII, Halpha and NII observation could provide. And neither your monitor could. It is however possible to use false-color techniques to map intensities (possibly normalized ones) to as many color channels as practical.
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Yes, Andrea. That's the sort of question I'm trying to find an answer for: if anyone is doing it, what colour mapping are they using to accommodate 4 data sets in a 3-channel colour space, without submerging one of the data sets? I suspect that I will try fiddling with my own combinations, but I would appreciate a "heads-up" on this as a way to be a bit more efficient - e.g. try someone's suggested palette, then try tweaking one/a few of the colours to see what I can achieve. I'm not trying to be scientific about this, I'm just trying to find a way to present 4 sets of data and end up with a pleasing result. If it can't be done, then I'll just shrug my shoulders and move on to the next challenge.
Paul.
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Hi Paul. I have been playing around recently with using dual band Ha/Oiii (L-Ultimate) and Sii/H-beta (Alp_T) filters with an OSC camera. I worked out contributions from each emission band based off my camera's QE curves/sensitivity at the specific emission lines for each filter. I use this to generate 4 channels: Ha, Oiii, Sii, and H-beta. I then have to evaluate whether to combine the H-beta with the Oiii or the Ha to get a result I like. Typically, it seems best with Oiii resulting in a lighter blue, but not always. It's a matter of personal taste here. I split the RGB channels for the L-Ultimate Ha/Oiii filter and the Alp-T Sii/Hbeta filter and use these equations to combine them. Equations are camera and filter specific so they would need some adjustments for other gear. Once your final channels are generated just process any way you like as a 3-channel NB image. Ha = 0.843*Ult_R + 0.115*Ult_G + 0.042*Ult_B Oiii = 0.035*Ult_R + 0.536*Ult_G + 0.429*Ult_B Sii = 0.789*ALP_R + 0.157*ALP_G + 0.054*ALP_B Hb = 0.032*ALP_R + 0.377*ALP_G + 0.591*ALP_B I average together Oiii and Hbeta to use as the Oiii channel, or Ha and Hbeta to use as the Ha channel. Again this is personal taste as each nebula seems to respond a bit differently in the result you get each way. Antlia has a much more simple method they posted in a video last year here: https://www.youtube.com/watch?v=q9h-Ag7E-iY . I personally like my method a little better for more contrast in the final image, but theirs is much easier and gives a decent result. None of the methods will give the clean separation of data you get with NB filters and a mono camera obviously. I was mainly just playing around trying to help find a way to do this for some members of a local astro club. My Rosette processed this way as an example: https://www.astrobin.com/425oc5/My apologies if this is not the question you were actually asking. I was having a difficult time following along with the conversation. There are a couple other images on my page using this technique so you can see the result I obtained. CS, Jeff Added Note: I believe I saw a post here recently from someone developing a Pixinsight script to do exactly this method. It is much newer than my work but I haven't found it to give you a link
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Jeff,
At last!, and many thanks, indeed. You are spot on! You are answering my initial query precisely: what are others doing to incorporate a 4th data set so that it doesn't immediately get lost (merged with the Ha, for example)?
I need to go through your processing regime carefully. I don't know what not taking account of the QEs will do - I have totally ignored them up to now. I'll look at Antlia's video, and give their method a trial to see what I get. It could be a good place for me to start. I have M8 data to work with, and am getting NGC2070 (Tarantula Nebula) over the next night or two.
Paul.
Added note reply: If that script materializes, Jeff, that would be an excellent and helpful starting point, and take some of the pain out of the manual processing. BTW: I forgot to commend you on your Rosette Nebula image - nice, and I'm a little jealous! Still, what's this game for but to try to equal, or better, what someone else has done?
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Thanks Paul. I will try and find the post about the script for you. This was all just a guess for me about how to do this when I started. I bet you can improve on it. Happy to help sharing more details about what I did if it is needed at any time.
CS,
Jeff
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Thanks a million, Jeff. I suspect I will take my time over this as there's a lot to get my ageing mind around. I'll post my attempt on this thread for anyone to comment on.
And CS for you, too.
Paul.
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Hi Paul, I can't find the script in this forum but here is a link to where it is talked about in the Pixinsight Forum. https://pixinsight.com/forum/index.php?threads/new-script-dbxtract.23344/ I'm sure it is the same one I thought I saw here a few months ago. And I just found a link to it here as well: https://www.astrobin.com/forum/c/equipment-forums/pleiades-astrophoto-pixinsight/new-script-dbxtract/It is quite a bit newer than the work I did but exactly the same principle. I don't think it accounts for H-beta filters like I use and you were talking about now that I look at it. I do see great explanations so you will see how I used the QE and Filter curves to get my H-Beta channel. Jeff
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