StarTools

...the journey may not be complete - more fiddling is always possible.

So this target came up and initially it seemed a good candidate for SHO, as there are quite a few beautiful tricolor images of it out there.

Alas, I kind of think all that is a little misleading.

This object and surrounds is a faint emissions region in Cygnus. The Ha itself is quite faint, though with 5 hours integration captured over a couple nights, it stretches out quite nicely. OIII was another story. Again I took two nights to capture about 5 hours, and while there's a little something there when stretched, the handful of OIII puffs are completely matched by dominant Ha. I tried an HOO, even one attempt dismissing any use of OIII for the Synth L, but the results were not appealing after the heavy throttling required to see even the faintest of blue (or ST being ST - teal).

This little blinky shows not only the disparity between Ha and OIII, but how any oxygen there is gets overlaid by strong Ha.


From discussions, I got the sense that SII was similarly sparse, so instead I acquired 2.5h of LRGB my next night out.

Here's a look at just the visual spectrum, giving a clue of just how faint even the "dominant" Ha is!


With the broadband as the base image, I tried both an LRGBHa and LRGBOIII using NB Accent. These worked reasonably well for what they were, and the stars looked pretty good (SVD worked fine), at least in versions not so heavily downsampled. I did use a pink reversal on the Ha version but not the OIII. Here's the LRGBOIII.

So, what to do with this? Was the two nights of OIII just a waste of time?

It struck me that the SHO versions of this floating around the internet may be a bit doctored, to more or less extent. At minimum, I think some renditions have different non-linear stretching applied to each emissions filter before compositing them together. I'm not super disturbed by that, we do our own independent weighting of an emissions band when adding to broadband via NB Accent. It's just that you would lose the relative emissions concentrations that ST typically maintains in those compositions. A lot of edits though seemed to be using OIII-based masks to reduce Ha where the OIII is, basically cutting a hole for the blue to show through. Or, pixel math of "dynamic" narrowband, which is a fancier and maybe smoother way of cutting the same hole. Meh. So all that I think can fool one into believing the target can make a legitimate SHO.

I did see one edit in HOO where the OIII was just whitening up those regions of combined emissions, and I liked that, so looked to find a way to include all 6 filters during some testing.

First, I took my Ha and OIII and composited that manually as a bicolor with Ha as R and OIII into G and B, but as RGB, RGB, and then saved out the linear file, in essence trying to create a duoband file. That then became my NB Accent data and I chose duo Ha/OIII for final compositing.

One problem I ran into was that the NB Accent, probably mostly the OIII component, was bloating and fading out the star colors with excessive teal. - Note that teal and cyan are the only OIII choices in NB Accent, which is very 1950's pastel I guess. In any event, this was difficult if not impossible to to a masked layer reversal of, even with fuzz, due to the nebulosity. And overall it also kind of wrecked any nice pinpointing done by SVD on the broadband synth L.

Ultimately what I did was to very lightly process the LRGB, meaning basically no enhancements, but in Color I boosted the saturation to 500%, with the intent to overwhelm the teal that would be imparted in the NB Accent step. It seemed to help. I balanced the Ha-OIII to like 55/45% and kept that, after which (even though this is backwards workflow) I tried out some sharpening and SVD. Now, SVD did not work so great and I imagine that is to be expected, with the stars' PSF's just a jumbled colored mess, but it did help a little bit. I think if there was a way to get enhancements, like deconvolution, into the separate NB Accent data before combining that all this could be smoothed over and things would match and look better.

After that I just ran a denoise. No SS or shrink, as the busy star field here seemed a feature to me rather than a bug.

Next I took a previously-processed LRGBHa (the one where reversal worked okay but included a good SVD) and layer blended that in at about 25%, which gave the Ha a needed boost of red features and fainter outer color. Finally, I just made a mask of the super tiny stars that had some ringing and used dering with no iterations and no color taming in the shrink module.

I think the end result is a somewhat reasonable LRGBHaOIII that fairly represents what is there in this faint, but star and Ha busy, region.

Anyone have any ideas on reworking the oddball workflow here for things to be better?

Oh and with the busy image, downsampling to anywhere near 500kb was pretty much impossible. So, here's a link through to a (still downsized) file in the CN gallery, and the astrobin staging area which has the full file. I think the full file might look better.


https://astrob.in/y21ilt/0/

Wow, great image, Mike! I like those busy, (true) colorful star fields with the hydrogen clouds.

My first impression was that it might look a bit cooler if the Ha wasn't so overwhelming but if the there was just dark space in the regions of faint Ha. That might add a bit of punch and give more emphasis on the beautiful star field. But that's an artistic decision of course. It might even take a bit of the depth...

How are your thoughts about balancing Ha and OIII in NBAccent? I am sometimes struggling. If I am fine with one gas and would just like to increase the intensity of the other, I have to adjust the strength slider but throttle back the contribution of the gas I originally liked with the balance slider. Sometimes I wish there was a separate slider for every single gas.

Regards
Stefan

Thanks Stefan, and good eye!

Normally at the very end I'll take a finished image into FilmDev to inspect the histogram shape and whatnot, and make usually small adjustments via gamma and DAF if something doesn't "look" right. Here though I didn't, possibly a bit reticent due to having already utilized a gamma drop in the NB Accent. But yes, too much overall red fog, likely a result of that final blend.

I made a slight alteration which only used a DAF of 3.0, no gamma, and that seemed enough to darken the background and up contrast a bit. I didn't want to vanish too much red nebula.

Yeah, our little see-saw narrowband slider in NB Accent follows the ST convention of single stretch and relative emissions.

Is it limiting? Perhaps, and a bit dependent on philosophy. As I did here, you can of course cheat a little if you have a separately processed but crop/bin matched version using only one of the gas filters. There are pitfalls possible, like my red fog, or bloating up stars and messing up a nice SVD on them.

Astrobin was updated:

https://astrob.in/y21ilt/0/

And link-through to the tweaked final.

Hi Mike,

looks good! Cleverly done with DAF...

Mike in Rancho wrote: ↑Tue Aug 01, 2023 5:26 am Yeah, our little see-saw narrowband slider in NB Accent follows the ST convention of single stretch and relative emissions.

Yes, I know. Just not sure if that makes too much sense with narrowband. I get it with broadband data to retain natural colors and ratios. But NB is somewhat different. Ratios depend on QE of the camera for the different bandpasses which are different for different cameras. So there isn't a *real* or *natural* ratio to maintain anyway, is it?

With the see-saw slider and the strength slider it's just more troublesome to get where you want it.

Mike in Rancho wrote: ↑Tue Aug 01, 2023 5:26 am There are pitfalls possible, like my red fog, or bloating up stars and messing up a nice SVD on them.

Mixing NB and broadband messes up the PSF anyway, right? Doesn't depend on cheating!?

Regards
Stefan

Hey Stefan,

Well, when the workflow goes in the normal direction ( ) and SVD is performed at the synth L stage well before any blending from NB Accent, the PSF's should be just fine. Assuming I have my ST time travel logic down right. Always tricky, that!

But I have been trying to think about the other kinds of stuff with compositing and just what NB is.

Possible imperfections in band QE don't bother me too much and I don't know if they would greatly affect the ratios. And if they did, they should be helping out weak OIII vs strong Ha, right? But there are other abstractions too, as discussed in prior threads, such that you still may require some extraneous information (filter exposure times, percentage of band throttling applied) to get any quantification of the relative emissions.

But I'm more musing about whether it should be mandatory that always treat our NB files in this relative-only manner. Are they tied at the hip somehow, like visual RGB must be, or can we ever deem them independent?

So while NB emissions balanced globally and relatively does provide documentary information, can we also get useful documentary information, perhaps focusing more in the spatial structure domain, while not being constrained by relativity of emissions?

NASA does that sort of thing often enough. JWST blends all sorts of wide, medium, and narrow IR bands, and I'm not sure they are holding things relative to each other. And many objects, famously Centaurus A for one, have been shown blended in three or even four types of data (visual, x-ray, IR, radio), all of which I figure have been independently stretched and false colors applied for both aesthetics and to show spatial locations along with possible interactions. I doubt any thought goes into the relative strengths of radio and x-ray, or that you'd necessarily have to fade one off in order to reveal the other.

But, can our usual compositing of Ha OIII, or SII Ha OIII, be thought of as fully independent structures that same way (as an alternative to relative), or must they be thought of only as a group? I dunno.

Of course independent processing and colorizing followed by layer operations may get to that point, albeit more messily and with extra work, and who knows how it would turn out.

Hi Mike!

Mike in Rancho wrote: ↑Thu Aug 03, 2023 7:24 am Well, when the workflow goes in the normal direction ( ) and SVD is performed at the synth L stage well before any blending from NB Accent, the PSF's should be just fine.

Yes, right. I was thinking if you do SVD AFTER NBAccent. Not recommended but feasible. Actually I do that pretty frequently.

Mike in Rancho wrote: ↑Thu Aug 03, 2023 7:24 am Possible imperfections in band QE don't bother me too much and I don't know if they would greatly affect the ratios.

Might not be an issue if using a 2600MC with QE being about 80% more or less for all visible wavelengths, but coming from a stock DSLR things might be different. QE might approach 80% in OIII region but about 25% in Ha. If you consider your camera a device for counting photons this might well change the photon count ratio by a factor of 2 or 3. Don't know how that translates in terms of stretching but assuming for our hypothetical 2600MC and the stock DSLR the QE for OIII being the same while having less signal for Ha with the DSLR...you probably need to stretch the Ha of the DSLR harder to get a similar result compared to the 2600MC. Or put differently, when you stretch the OIII of 2600MC and DSLR identically you get pretty much the same result. But translating that stretch to the two Ha datasets will lead to two different results since both had very different photon counts.

So of course both ratios are real (i.e. measured) but this ratio not necessarily has something to do with reality in space (i.e. ratio of photons emitted or amount of gas/number of gas molecules/atoms) UNLESS you take QE into account. So I doubt that the ratio thing is so important with NB data to keep your image documentary.

Mike in Rancho wrote: ↑Thu Aug 03, 2023 7:24 am And many objects, famously Centaurus A for one, have been shown blended in three or even four types of data (visual, x-ray, IR, radio), all of which I figure have been independently stretched and false colors applied for both aesthetics and to show spatial locations along with possible interactions.

Ha! While thinking about the issue EXACTLY this and especially Centaurus A came to my mind And I think it's a great example questioning the ratio requirement for NB images.

Mike in Rancho wrote: ↑Thu Aug 03, 2023 7:24 am But, can our usual compositing of Ha OIII, or SII Ha OIII, be thought of as fully independent structures that same way (as an alternative to relative), or must they be thought of only as a group? I dunno.

Yeah, good question. I am not sure either. But the x-ray and radio and Ha signals are basically all electromagnetic radiation. Only thing is that OIII and Ha are part of the visual spectrum. I don't know if this justifies treating them so differently.

Mike in Rancho wrote: ↑Thu Aug 03, 2023 7:24 am Of course independent processing and colorizing followed by layer operations may get to that point, albeit more messily and with extra work, and who knows how it would turn out.

Agreed. I'd like to skip all the messing with layering and extra work and instead apply independent processing of NB channels Again I feel it's unnecessarily limiting. But that said, I am not sure about the whole thing...

Regards
Stefan

Right Stefan, worthy of consideration anyway. And not so much that relative emissions has potential flaws, but just as another optional method of displaying factual information, albeit more spatial than relative. As a side effect I think it may also present fairly more appealing imagery, particularly in bicolor. Of course truly weak emissions will still be dominated, no getting around that without unwanted trickery.

Practical matters may also cause some headache, though.

Right now coding is probably more efficient and dovetails with visual Color also being linearly relative. So we are probably talking major revamp of how things work (ST 2.0?).

What sounds good in theory may be pretty ragged in application. Some of the similar stuff we see may be reliant on things like star removal, a road we really don't want to go down, as a way of avoiding star and continuum effects. We already experience this somewhat when utilizing NB Accent.

While it wouldn't directly help full NB images like bicolor and tricolor, it could be nice just to add independent NB Accent for more than one band - rather than the single relative slider in the step 2 window. So, maybe by way of some dropdown menu or one of our usual multi-toggle buttons, you would do the step 1 stretch differently for say Ha and then OIII, and then likewise as to step 2, hit keep when happy.

I don't want to think what that would do to tracking though.

And there's still the issue of the NB Accent files skipping out on most enhancement, as well as the color choice limitations. That in itself as a global upgrade across modules (1.10?) I think would be useful - true fully variable false color mapping.

Or we could just let Ivo take a well deserved vacation.

Mike in Rancho wrote: ↑Mon Jul 31, 2023 4:53 pm I did use a pink reversal on the Ha version

Maybe I once knew what is this "pink reversal" - but I've already forgotten most of what I ever learned... Could you explain for the denser amongst us?

Hi Mike,

oh yeah, I have no idea what this modification would mean for the app in terms of algorithms or programming

Regards
Stefan