In overlay matte, use the luminance as a matte instead of each individual color compo...

[movit] / lift_gamma_gain_effect.h

diff --git a/lift_gamma_gain_effect.h b/lift_gamma_gain_effect.h
index 6364eeb00b6c41b79f894b1da231cb44cdfac240..533a7b2f22aee450c33eef9a41f4a42d657ce7a0 100644 (file)
--- 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 {
@@ -8,7 +24,7 @@ public:
        LiftGammaGainEffect();
        std::string output_fragment_shader();
 
-       void set_uniforms(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num);
+       void set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num);
 
 private:
        RGBTriplet lift, gamma, gain;