OSC Optolong l-eNhance colour

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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Re: OSC Optolong l-eNhance colour

Post by admin »

Chunkles wrote: Sun Nov 22, 2020 12:26 am using the L-enhance filter:

use things like the Hubble palette
Hi Scott,

I'm afraid that is not physically possible. A HST-palette image consists of three bands, namely S-II, H-alpha and O-III, mapped to red, green and blue respectively (e.g SHO:RGB).

The L-enhance filter records Ha, no S-II and records H-beta and O-III lumped into one band. E.g. you are short one band, while to O-III band will be mixed with H-beta signal as well.

The best(and most popular thing to do) you can do, is to create a bi-color as suggested in this thread.
A red/cyan rendering HOO rendering is the most popular as it shows where Ha emissions are, and where O-III/H-beta emissions are, while also roughly corresponding to their location in the visual spectrum.

So (in 1.7) load your data like this in the Compose module;
Selection_288.jpg
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Process your image (in mono), then, once you hit the Color module, use the Bi-Color preset and tweak to taste. Note you can use the Matrix option to flip between other popular channel mappings besides HOO (a feature unique to StarTools thanks to Tracking and being able to do color calibration so late in the workflow). Be prepared for a lot of blue stars as stars don't show up well in Ha (but do so in the O-III through Hb part of the spectrum).
StarTools_289.jpg
StarTools_289.jpg (366.57 KiB) Viewed 389 times
Shrink the stars if you want and/or push them back with the Super Structure module.
NewComposite.jpg
NewComposite.jpg (221.83 KiB) Viewed 388 times
Hope this helps!
Ivo Jager
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Re: OSC Optolong l-eNhance colour

Post by mgutierrez »

Hi Ivo,

Please let me do a newbie question.
What's the point of composing an image from a rgb one? I intuitively get it, but when I think it twice I get confused. When shooting with a mono camera with filters, I get it; you have forcibly to compose and mount the image. But when you are dealing with a color image taken with the l-enhance filter, you already have the image composed with a red channel "filled" with Ha data (wavelengths roughly matches), green channel with Hb info, and blue channel with Oiii (last two ones more or less overlaps). Is right this approximation or it's a nonsense? If it makes more or less sense, which is the advantage? Build the Illuminance channel? Which is the logic behind?

Thanks!
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Re: OSC Optolong l-eNhance colour

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mgutierrez wrote: Wed Nov 25, 2020 8:46 pm What's the point of composing an image from a rgb one? I intuitively get it, but when I think it twice I get confused. When shooting with a mono camera with filters, I get it; you have forcibly to compose and mount the image. But when you are dealing with a color image taken with the l-enhance filter, you already have the image composed with a red channel "filled" with Ha data (wavelengths roughly matches), green channel with Hb info, and blue channel with Oiii (last two ones more or less overlaps). Is right this approximation or it's a nonsense?
Indeed, you are correct that the channels already roughly correspond to a red/cyan bi-color. Importing through the Compose module formalises that this is a narrowband dataset (in addition to giving some more flexibility with regards to compositing). With the application knowing that this is a narrowband dataset (and not a visual spectrum dataset), it knows - amongst other things - what to show you in the Matrix option in the Color module for example. A visual spectrum dataset from a DSLR will show vendor and model-specific color matrices, while a narrowband dataset will allow for extensive channel remappings (as the color rendition is regarded as false color).

Coloring will also definitely differ between a dataset whose coloring is left as RGB versus a dataset whose coloring is forced to R(G+B)(G+B). The latter will yield a bi-color image where the coloring is comparable predictable and identical, no matter whether you use a duoband filter, tri-band filter or quad-band filter, and no matter what the response of your sensor may be to the different bands (e.g. whether your camera is, for example, Ha modded or not). And as you know, replicability and consistency is a highly sought after attribute in photography and science!

Hope this helps and makes sense!
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Re: OSC Optolong l-eNhance colour

Post by mgutierrez »

Thanks for the explanation, Ivo; it makes sense! One last question. Do I need to double the green exposure compared to red and blue when composing?
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Re: OSC Optolong l-eNhance colour

Post by Chunkles »

Thanks Ivo! That completely makes sense and is very helpful!
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Re: OSC Optolong l-eNhance colour

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mgutierrez wrote: Thu Nov 26, 2020 8:52 am Do I need to double the green exposure compared to red and blue when composing?
In 1.7 you don't, as long as you choose the long-but-descriptive 'L + Synth L From R(2xG)B, R(GB)(GB) (Bi-Color from OSC/DSLR)' option. The 'R(2xG)B' bit before the comma denotes luminance is re-weighted for you to incorporate 2x the green channel. So, just select this option, load the same dataset in each of the slots and you should be good to go. The Compose module does all the dirty work. :thumbsup:
Ivo Jager
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Re: OSC Optolong l-eNhance colour

Post by mgutierrez »

admin wrote: Fri Nov 27, 2020 12:50 am In 1.7 you don't, as long as you choose the long-but-descriptive 'L + Synth L From R(2xG)B, R(GB)(GB) (Bi-Color from OSC/DSLR)' option. The 'R(2xG)B' bit before the comma denotes luminance is re-weighted for you to incorporate 2x the green channel. So, just select this option, load the same dataset in each of the slots and you should be good to go. The Compose module does all the dirty work. :thumbsup:
got it!!! thanks ivo!
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