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From a SNR perspective
For some nebulae the flux rate of Blue (and even Green) is often quite low - especially compared to Red.
In order to get the blue signal significantly above the noise floor and get a good SNR you may choose/need to expose for longer than say R or L
If you are relying on the R signal or the L signal which will usually be strong having a good flux rate then your Blue may still be buried deeper in the noise
In any case there is still the issue SNR to consider and generating something artificially is going to either obfuscate or abstract the problem making it harder to resolve.
As Ricks spectral response curves shows the real formula for the Astrodon Series 2 filters ends up looking more like this :
L = B+G - (BG overlap) + (Notch between G&R) + R + (extended Red)
This is nothing like L = B+G+R !
What the CCD is actually recording is different again since it has its own set of spectral response curves and these further distort what the filter might theoretical capture and how efficiently the CCD is actually converting eacg spectral range into signal
That would dramatically impact on the modified L=RGB formula above !
Making it very non linear and with all sorts of offsets
At the end of the day - after white balancing and fine tuning colour to "taste" you'll get enough signal to render an image.
Then that probably boils down to beauty is in the eye of the beholder
I think you are always going to be better off with more data than less data, but of course the quest for more efficiency - ie potentially 25% less imaging time is attractive.
The simple maths shows its not the same (the more complicated Maths including CCD response, atmospheric response (as stated above also), SNR issues, scope response etc etc shows its significantly different
Given the large notch between G & R (approaching 25% of L signal and the other 10% of extended R) and the
That shows that a simple B=L - (R+G) could potentially affect B by up to 35% of L !!! and this could be quite problematic.
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