LRGB SynthLum - best method?

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LRGB SynthLum - best method?

Postby Amaranthus » Wed Apr 01, 2015 12:23 am

Ivo or others, I'd like some feedback on what you consider is the best method for creating a synthetic luminance image in StarTools using LRGB filters (i.e. a LLRGB or HaRGB for instance).

My standard method has been this:
1. Load the R monochromatic channel using "Open", wipe (use temporary autodev to check), then denoise, then save. Repeat for G and B. Keep these as my 'clean' but unstretched chrominance channels, RC, GC and BC.
2. Prepare the monochromatic L channel (dev, wipe, HDR, contrast, deconv, denoise, etc.) and save. Repeat this procedure for each of the R, G and B channels, and save as RL, GL and BL.
3. Use Layer module to do an iterative weighted blend of the L, RL, GL and BL channels. Save SynthLum.
4. Use LRGB to open the SynthLum in the L channel, and RC, GC and BC in the colour channels.
5. Fire up the Colour module, do colour balancing etc.
6. Do final touch-ups, including a wipe check, further HDR if required, plus other stuff like Life or Repair etc.

This seems to work out pretty well. However, I can see that there might be other ways to do it. One that occurred to me was to FIRST use the LRGB module to load up the R, G and B channels only, and then do step 2 from the above on this composite, but including the colour balancing etc. Save this as an RGB-L. Then do a separate process of the Luminance monochrome data. Then, as a final step, do the weighted combination in Layer.

Both methods would preserve the correct colour saturation levels, but the latter strikes me as simpler. But the final Layer step might desaturate the colour. Would it be effective do you think? (I guess I can road-test it!). Or do people have other workflows for LLRGB?
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Re: LRGB SynthLum - best method?

Postby Packen » Fri Nov 27, 2015 11:44 am

I don't see a response to your question, the methodology of Ha,R,G,B Synthesis posted back in November 2012 indicated that later versions of StarTools would address the LRGB tool and the multi steps to generate the Luminous channel would be avoided.
I have been using the tool with LRGB imaging for a while and am not sure if the subsequent sharpening etc. is only done on the L or on the colours as well.

I am about to add a Ha filter to my filter wheel and am interested in how to integrate the Ha into the process.
I would be interested in how others do this, clearly the approach of Nov. 2012 is now out of date.

The procedure stated above looks interesting, did this work out or is there another way?.

Any help would be appreciated.

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Re: LRGB SynthLum - best method?

Postby Amaranthus » Sun Nov 29, 2015 2:15 am

Packen, I've typically used Ha as a substitute for L. Others blend it with the R channel, but it tends to affect colour in unrealistic ways.

See here for an example of a HaRGB I did recently: viewtopic.php?f=11&t=737
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Re: LRGB SynthLum - best method?

Postby Packen » Sun Nov 29, 2015 8:13 am

Thanks for your reply and the link, I followed the link to Astrobin and am now following you.

After I asked the question above I discovered a much later HaRGB procedure posted by Ivo on the 9th Dec 2014.

I have tried it out with existing LRGB data and am quite impressed by the results.
Ivo's recommendation there was to only include the Ha in the Lum with weighted amounts of R, G and B, not to add it to the Red channel, so I will try that.

The next question, is it worth taking straight L subs or just take the R, G and B in that they all end up in the SynthLum and the added colour subs would help with the overall colour noise.

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