The first few lines are just setting up some handy functions and a node for my gamma correction value.

def PM(x, lbl): return Add(x).labelled("PM:" + lbl)
gamma = PM(2.2, "Gamma")
def AGC(item): return item ** gamma
def GC(item): return item ** (1 / gamma)

PM makes a parameter node - takes a number and a label.
gamma is our default gamma value.
AGC is anti-gamma correction - use it on any incoming colors.
GC is our gamma correction - use it at the end to make the final output color.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)