#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 {
public:
LiftGammaGainEffect();
+ virtual std::string effect_type_id() const { return "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;