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LRGB ratio

Bruce Donzanti
in PixInsight
Adam

I'm primarily a NB imager (mostly due to my Bortle 7 sky).  However, I've had some recent success with some LRGB and HaLRGB galaxy images, following a couple of your examples to help me along, especially in creating a superLum.  I confess I have not watched all of the LRGB/RGB-related videos, but I will eventually get to them.  In the meantime, I want to ask if you have a recommended LRGB ratio (e.g., 2:111, 3:111, etc.) starting point. I realize seeing conditions, the object in question, etc. can alter things, but just speaking in general, as a recommended starting point.  I also ask because there has been a ton of discussion on Astrobin and other sites about RGB vs. LRGB as it pertains to SNR, sharpness, and the ratios of the L vs. RGB filters, and the debates lead to a lot of confusion.

Bruce

Comments

  • BlockHeadBlockHead
    edited March 23
    I do not think LRGB as it was originally implemented is now very helpful with CMOS sensors. There is no readnoise benefit to acquiring binned color data. Disregarding that statement- even if you expose unfiltered data- yes you can get better S/N per time when acquiring with an L at the telescope. But... if you actually succeed- then you end up exceeding what the RGB can actually color well (because it is *noisier* by comparison). So then you take more RGB...a vicious cycle.

    That is why SuperLumRGB is probably the best choice in more circumstances. Just combine the RGB data for a Luminance. Never a harm in that. 

    Anyway, to answer your question- back in the day when it made sense to do so- I often exposed on faint objects with a minimum of 10 hours total time divided between 4 hours of Lum and 2 in each of RGB... So that was indeed 2:1:1:1 .

    -the BLockhead
  • Bruce Donzanti
    ahh..ok, this is good info to know.  I never considered the CCD vs. the CMOS aspect of this.

    Frankly, I've never done a 2 or 3:1:1:1 ratio, mainly because I have limited hours per object due to clouds, winds, moon, etc.  So, I often only get a few more frames of L vs. the rest due to these practical reasons, but you can still get a pleasant image with surprisingly good detail.  Not award winning but nonetheless, folks should not be persuaded to give up on broadband imaging under LP skies, given the current technology.

    thx again  
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