From 8448764aae2315fe93d5d0b74d5077d21b2e35bd Mon Sep 17 00:00:00 2001
From: Ahmet Inan <ainan@mathematik.uni-freiburg.de>
Date: Sun, 15 Dec 2013 14:28:08 +0100
Subject: [PATCH] added linear_srgb and srgb_linear

---
 yuv.c | 23 +++++++++++++++++++++++
 yuv.h |  2 ++
 2 files changed, 25 insertions(+)

diff --git a/yuv.c b/yuv.c
index 7486ffa..6688245 100644
--- a/yuv.c
+++ b/yuv.c
@@ -7,6 +7,7 @@ You should have received a copy of the CC0 Public Domain Dedication along with t
 
 
 #include "yuv.h"
+#include <math.h>
 
 uint8_t yuv_clamp(float x)
 {
@@ -14,6 +15,28 @@ uint8_t yuv_clamp(float x)
 	return tmp > 255.0 ? 255.0 : tmp;
 }
 
+uint8_t linear_srgb(float linear)
+{
+	float v = fminf(fmaxf(linear, 0.0f), 1.0f);
+	float K0 = 0.03928f;
+	float a = 0.055f;
+	float phi = 12.92f;
+	float gamma = 2.4f;
+	float srgb = v <= K0 / phi ? v * phi : (1.0f + a) * powf(v, 1.0f / gamma) - a;
+	return 255.0f * srgb;
+}
+
+float srgb_linear(uint8_t srgb)
+{
+	float v = srgb / 255.0f;
+	float K0 = 0.03928f;
+	float a = 0.055f;
+	float phi = 12.92f;
+	float gamma = 2.4f;
+	float linear = v <= K0 ? v / phi : powf((v + a) / (1.0f + a), gamma);
+	return linear;
+}
+
 uint8_t R_YUV(uint8_t Y, uint8_t U, uint8_t V)
 {
 	(void)U;
diff --git a/yuv.h b/yuv.h
index a068e02..7c251e5 100644
--- a/yuv.h
+++ b/yuv.h
@@ -10,6 +10,8 @@ You should have received a copy of the CC0 Public Domain Dedication along with t
 #define YUV_H
 #include <stdint.h>
 
+uint8_t linear_srgb(float linear);
+float srgb_linear(uint8_t srgb);
 uint8_t R_YUV(uint8_t, uint8_t, uint8_t);
 uint8_t G_YUV(uint8_t, uint8_t, uint8_t);
 uint8_t B_YUV(uint8_t, uint8_t, uint8_t);