To my knowledge QCUIAG member TG Tan was the first to use YRGB post processing, whereby the Y channel is used as luminence layer.
TG Tan has an extensive description on his website and I recommend you to go there and study his very valuable technique, which he has described with great care and with many examples.

But time does not stand still and further developments have turned me to LRBG Imaging and Post Processing.