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RGB or LRGB?

LRGB RGB
Light Polluted skies •12 replies•394 views
Rob Johnson avatar
Rob Johnson avatar
I’ve always assumed that LRGB is the way to go to image in colour but recently I seem to be having much more success with RGB.
my thought is that in RGB the background is much lower and easier to manage as I’m filtering to a specific part of the spectrum and gaining a better s/n.

Anyone else find working in RGB better?

Im aware you can combine the RGB channels to make a luminance channel  But I haven’t tried this method yet.
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Jerry Yesavage avatar
Jerry Yesavage avatar
You may want to expose the L less than the RGB (shorter time) but for more frames… your milage may vary…. you may also consider different exposure lengths and use HDR techniques… I think I have some M13 images like that.  Best for objects where core is burned out.

Was M5 the latest:

https://www.astrobin.com/ehah6g/?nc=user
Rob Johnson avatar
Rob Johnson avatar
Nice image Jerryyyyy, yes I guess I could do less exposure on the Luminance or my thinking would be greater exposure on the RGB as the backgrounds are much lower. I'll try and do a comparison and see what the outcome is.

Thanks,
Rob
Ben Koltenbah avatar
Ben Koltenbah avatar
Rob:

Many RGB filters do indeed cut out certain parts of the spectrum that are more dominated by light pollution.  My Astrodon filters, for example, are designed that way.  I recall there's a gap between the green and the red to mask out sodium street lights.  And, of course, a luminance filter does not typically have any gaps through the visual spectrum unless it is specifically designed as a light pollution filter.  With the increased use of a wider variety of lights, however, there is light pollution contribution growing all over the spectrum.

Ben
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Chris Sullivan avatar
Chris Sullivan avatar
I find that my luminance filters are pretty useless, however, replacing the luminance with a broadband light pollution filter (e.g., Optolong L-Pro, Orion SkyGlow Astrophotography Filter, Baader Moon & Skyglow and the Chroma LoGlow) has given me excellent results. Like the RGB filters, they also cut out just where light pollution is the strongest while letting everything else in. I only use them on galaxies though, but I would probably try them on reflection nebulae if I were to image them.
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noon avatar
noon avatar
I have done away with my Lum data and go purely RGB. Personally, the Lum data introduces a lot more gradients than my RGB data and tends to wash out colors in the integrated image. I have been happier with my images since I just spent the extra "Lum" time on more RGB subframes and overall they have been easier to process.
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Derek Spratt avatar
Derek Spratt avatar
I have generally avoided taking Lum data when I have been imaging in my urban B7 skies for the reasons mentioned above - very sensitive to LP, bloating stars and strong gradients. This is not the case in B2 skies though where I can get great results from adding some Lum data for enhanced detail when I have limited time at a dark sky site - it can wash out colours if not added carefully though and I still mainly focus on gathering RGB data with Lum as a 'sweetener'. So count me in as an RGB imager (I actually do a lot of narrowband from my B7 skies with great results). Adding Lum data is a time-saving 'cheat' only - if you have the time to grab lots of RGB data and do it properly you won't gain much of an advantage using Lum data, sorry. You just can't break the laws of physics.
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Tareq Abdulla avatar
Tareq Abdulla avatar
It will be nice to see someone under Bortle 7/8/9 doing LRGB and for a target be it Orion or M45 or even Andromeda then process TGB alone for S-Lum then process again with real Lum filter added in the results and compare to see how much bad added Lum filter is under those heavy LP skies, also many said using UV/IR cut filter with a color camera will help to prevent bloated stars, so how come added Lum or UV/IR cut will introduce bloated stars, big contradiction.
Alexandre Fagundes avatar
Alexandre Fagundes avatar
I think that the L filter can apply a lot of specific details to the nebulae and, it greatly improves the definition of the stars and their spikes (generated by Newtonians).
Tareq Abdulla avatar
Tareq Abdulla avatar
Alexandre Fagundes:
I think that the L filter can apply a lot of specific details to the nebulae and, it greatly improves the definition of the stars and their spikes (generated by Newtonians).

I will use L filter when applicable, i keep thinking about RGB first, should i use OSC or mono, if OSC then L is not included, if mono then i will do L too, but will it be bad if i added L from mono to RGB from OSC?!!!
Alexandre Fagundes avatar
Alexandre Fagundes avatar
Tareq Abdulla:
Alexandre Fagundes:
I think that the L filter can apply a lot of specific details to the nebulae and, it greatly improves the definition of the stars and their spikes (generated by Newtonians).

I will use L filter when applicable, i keep thinking about RGB first, should i use OSC or mono, if OSC then L is not included, if mono then i will do L too, but will it be bad if i added L from mono to RGB from OSC?!!!

I think it's worth trying!
Tareq Abdulla avatar
Tareq Abdulla avatar
Alexandre Fagundes:
Tareq Abdulla:
Alexandre Fagundes:
I think that the L filter can apply a lot of specific details to the nebulae and, it greatly improves the definition of the stars and their spikes (generated by Newtonians).

I will use L filter when applicable, i keep thinking about RGB first, should i use OSC or mono, if OSC then L is not included, if mono then i will do L too, but will it be bad if i added L from mono to RGB from OSC?!!!

I think it's worth trying!

You are right!
Vroobel avatar
Vroobel avatar
Hi, 

Rob, as it was mentioned earlier, also imo the more shorter L subs do the job. I follow the rule of the total integration time L = R+G+B like below, which is easy to do with NINA:

6x 15s L, 1x 30s R, 1x 30s G, 1x 30s B

I repeat it continuously doing a dithering every iteration. Shorter L subs bring less LP while their number increases the SNR. Also, I follow the PixInsight authors' tutorials and do a synthetic luminance. 

There is a significant cost of the high number of L subs: the stacking time in case of the PI. 

CS, Martha 
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