1 #ifndef _MOVIT_LIFT_GAMMA_GAIN_EFFECT_H
2 #define _MOVIT_LIFT_GAMMA_GAIN_EFFECT_H 1
4 // A simple lift/gamma/gain effect, used for color grading.
6 // Very roughly speaking, lift=shadows, gamma=midtones and gain=highlights,
7 // although all parameters affect the entire curve. Mathematically speaking,
8 // it is a bit unusual to look at gamma as a color, but it works pretty well
11 // The classic formula is: output = (gain * (x + lift * (1-x)))^(1/gamma).
13 // The lift is actually a case where we actually would _not_ want linear light;
14 // since black by definition becomes equal to the lift color, we want lift to
15 // be pretty close to black, but in linear light that means lift affects the
16 // rest of the curve relatively little. Thus, we actually convert to gamma 2.2
17 // before lift, and then back again afterwards. (Gain and gamma are,
18 // up to constants, commutative with the de-gamma operation.)
20 // Also, gamma is a case where we would not want premultiplied alpha.
21 // Thus, we have to divide away alpha first, and then re-multiply it back later.
30 class LiftGammaGainEffect : public Effect {
32 LiftGammaGainEffect();
33 virtual std::string effect_type_id() const { return "LiftGammaGainEffect"; }
34 virtual AlphaHandling alpha_handling() const { return INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK; }
35 std::string output_fragment_shader();
37 void set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num);
40 RGBTriplet lift, gamma, gain;
45 #endif // !defined(_MOVIT_LIFT_GAMMA_GAIN_EFFECT_H)