X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=lift_gamma_gain_effect.h;h=b57a89964204fa5622635ac852d8678721a090ce;hp=6364eeb00b6c41b79f894b1da231cb44cdfac240;hb=e8650c7b7814c5beef59059b8acac3e5e7b8ddc6;hpb=b77dca09201f3373c5466d695338e1e29406072b

diff --git a/lift_gamma_gain_effect.h b/lift_gamma_gain_effect.h
index 6364eeb..b57a899 100644
--- a/lift_gamma_gain_effect.h
+++ b/lift_gamma_gain_effect.h
@@ -1,6 +1,22 @@
 #ifndef _LIFT_GAMMA_GAIN_EFFECT_H
 #define _LIFT_GAMMA_GAIN_EFFECT_H 1
 
+// A simple lift/gamma/gain effect, used for color grading.
+//
+// Very roughly speaking, lift=shadows, gamma=midtones and gain=highlights,
+// although all parameters affect the entire curve. Mathematically speaking,
+// it is a bit unusual to look at gamma as a color, but it works pretty well
+// in practice.
+//
+// The classic formula is: output = (gain * (x + lift * (1-x)))^(1/gamma).
+//
+// The lift is actually a case where we actually would _not_ want linear light;
+// since black by definition becomes equal to the lift color, we want lift to
+// be pretty close to black, but in linear light that means lift affects the
+// rest of the curve relatively little. Thus, we actually convert to gamma 2.2
+// before lift, and then back again afterwards. (Gain and gamma are,
+// up to constants, commutative with the de-gamma operation.)
+
 #include "effect.h"
 
 class LiftGammaGainEffect : public Effect {