Load and manipulate wide-field RGB in Compose

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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SBRToolMichigan
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Load and manipulate wide-field RGB in Compose

Post by SBRToolMichigan »

Greetings all!

I've had some good results so far in loading narrowband frames into Compose and processing away. I was wondering now if there is a way to load, manipulate and process separate multiple RGB files that have already been aligned and combined elsewhere into Compose?

For example, say I have three RGB files that represent stacks of a regular OSC session, a mono Ha session, and a multiband OSC session with a L-eXtreme filter. Depending on the mix, one RGB file may be dominant over the others and needs to be attenuated. To accomplish that, I tried several different ways to assign the files to the Red Green and Blue channels so I could hopefully use the Total Exposure sliders to emphasize say, one file over the others. Didn't seem to work for me...the respective channel color always tinted the result.

I've searched most of the tutorials that I've found but didn't come across anything that was encouraging so far. Is what I want to do just wishful thinking? Thanks for any suggestions!

Craig
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Re: Load and manipulate wide-field RGB in Compose

Post by admin »

Hi Craig,

I'm having a little trouble understanding what you are trying to do or why you (appear to?) be combining/mixing all sorts of parts of the spectrum?

The Exposure sliders are explicitly not for the purpose of coloring; they are for the purpose of creating a synthetic luminance master. Of course, such a master cannot be created in a meaningful way by mixing datasets that cover wildly different parts of the spectrum... It's like mixing a separate single violin, a separate string section, with a noisy recording of the full orchestra. It's not going to make the full recording's fidelity any better - at most you will be able to render a louder violin or string section with a (comparatively) attenuated, still noisy orchestra. This of course defeats the purpose of recording the full orchestra in the first place. However you can divide up your full orchestra/"spectrum" into 3 sections bass, strings, percussion (RGB), record those separately and then add them together; they will perfectly complement each other and cover the full orchestra. Now you can add that to recordings of the full orchestra, as they essentially recorded the same thing. That's what synthetic luminance frame generation does (R+G+B becomes synthetic L, which can be either processed as is, or added to "real" L). Narrowband of any sort does not work that way.

The compose module serves two purposes; 1. create a luminance (detail) signal master 2. create an entirely separate chrominance (color) master. This is so that - unlike other software - detail and color processing do not cross-contaminate each other.

If I am completely off the mark, would you be able to explain what you are trying to do in more detail?
Ivo Jager
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SBRToolMichigan
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Re: Load and manipulate wide-field RGB in Compose

Post by SBRToolMichigan »

Thanks Ivo!

I appreciate your orchestral illustration of what I'm trying to accomplish. I see it as akin to mixing, say, three different recordings of concerts by the Boston Pops performing "Rhapsody In Blue". Each performance may have attractive attributes that came out better than in the other recordings and therefore encourage an emphasis. Applying that concept to AP, I've recently been trying to balance a OSC stack of M81/82 taken with a new L-eXtreme multiband filter that has nice Ha (violin if you will) detail with a broadband OSC stack that has the dominant galaxies (brass sections) So far, I can only emphasize one or the other but not balance both files to my satisfaction.

Does that better explain what I'm trying to accomplish? It does sound though that this effort is beyond the scope and purpose of the wonderful compose module. I'm sure there's another way to do this but I just haven't come across it yet.

Thanks so much for your time and best wishes,
Craig
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Re: Load and manipulate wide-field RGB in Compose

Post by admin »

Thanks Craig,
SBRToolMichigan wrote: Mon Jan 11, 2021 3:04 pm I see it as akin to mixing, say, three different recordings of concerts by the Boston Pops performing "Rhapsody In Blue". Each performance may have attractive attributes that came out better than in the other recordings and therefore encourage an emphasis.
My point was to illustrate that this too is impossible in audio signal processing by simple mixing; the existing violin of the full-orchestra recording is still there and is impossible to isolate and remove to substitute your new violin. Sure, you can mix in your new violin where it will double-up with the old violin from the full-orchestra. The silence in the violin-only recording will attenuate the rest of the orchestra by a factor of 2, though adding any noise in the violin-only signal to the final recording. This is presumably not what you are after (and this is the reason why what you're trying to do does not typically make sense).

The compose module is indeed meant for compositing the cleanest possible signal and not (really) for arbitrary, unrelated, signal blending. It can, however be (ab)used as such, though any notion of specific signal contribution (from a physics point of view) goes out of the window.

You can, if you really want, create mono stacks out of the signals you want to mix (for example, import each as Luminance File only, then saving them), and then, once again in the Compose module import them as R, G and B, while setting 'Luminance, Color" to "L + Synthetic L From RGB, Mono". You can then use the red, green and blue Exposure sliders as a way to 'mix' them and create a synthetic luminance signal. Save that, and then, re-launching the Compose module, use that signal for your luminance file, importing regular red, green and blue for Red, Green and Blue files, while setting 'Luminance, Color' to 'L, RGB'.

There is a reason why there are no tutorials for what you are trying to do (not for ST, not for other software), as what you are proposing to do does not make sense in most situations. The closest would maybe be the practice of using Ha to accentuate an LRGB stack, but here too there are many ways of doing that (and none should involve simply adding Ha to luminance!).
Ivo Jager
StarTools creator and astronomy enthusiast
SBRToolMichigan
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Joined: Mon Oct 26, 2020 1:11 am

Re: Load and manipulate wide-field RGB in Compose

Post by SBRToolMichigan »

Thanks Ivo...I always appreciate your insight and suggestions!

Craig
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