/work/libwebp/sharpyuv/sharpyuv_gamma.c

Source
// Copyright 2022 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Gamma correction utilities.

#include "./sharpyuv_gamma.h"

#include <assert.h>
#include <float.h>
#include <math.h>

#include "./sharpyuv.h"
#include "webp/types.h"

// Gamma correction compensates loss of resolution during chroma subsampling.
// Size of pre-computed table for converting from gamma to linear.
#define GAMMA_TO_LINEAR_TAB_BITS 10
#define GAMMA_TO_LINEAR_TAB_SIZE (1 << GAMMA_TO_LINEAR_TAB_BITS)
static uint32_t kGammaToLinearTabS[GAMMA_TO_LINEAR_TAB_SIZE + 2];
#define LINEAR_TO_GAMMA_TAB_BITS 9
#define LINEAR_TO_GAMMA_TAB_SIZE (1 << LINEAR_TO_GAMMA_TAB_BITS)
static uint32_t kLinearToGammaTabS[LINEAR_TO_GAMMA_TAB_SIZE + 2];

static const double kGammaF = 1. / 0.45;
#define GAMMA_TO_LINEAR_BITS 16

static volatile int kGammaTablesSOk = 0;
void SharpYuvInitGammaTables(void) {
  assert(GAMMA_TO_LINEAR_BITS <= 16);
  if (!kGammaTablesSOk) {
    int v;
    const double a = 0.09929682680944;
    const double thresh = 0.018053968510807;
    const double final_scale = 1 << GAMMA_TO_LINEAR_BITS;
    // Precompute gamma to linear table.
    {
      const double norm = 1. / GAMMA_TO_LINEAR_TAB_SIZE;
      const double a_rec = 1. / (1. + a);
      for (v = 0; v <= GAMMA_TO_LINEAR_TAB_SIZE; ++v) {
        const double g = norm * v;
        double value;
        if (g <= thresh * 4.5) {
          value = g / 4.5;
        } else {
          value = pow(a_rec * (g + a), kGammaF);
        }
        kGammaToLinearTabS[v] = (uint32_t)(value * final_scale + .5);
      }
      // to prevent small rounding errors to cause read-overflow:
      kGammaToLinearTabS[GAMMA_TO_LINEAR_TAB_SIZE + 1] =
          kGammaToLinearTabS[GAMMA_TO_LINEAR_TAB_SIZE];
    }
    // Precompute linear to gamma table.
    {
      const double scale = 1. / LINEAR_TO_GAMMA_TAB_SIZE;
      for (v = 0; v <= LINEAR_TO_GAMMA_TAB_SIZE; ++v) {
        const double g = scale * v;
        double value;
        if (g <= thresh) {
          value = 4.5 * g;
        } else {
          value = (1. + a) * pow(g, 1. / kGammaF) - a;
        }
        kLinearToGammaTabS[v] = (uint32_t)(final_scale * value + 0.5);
      }
      // to prevent small rounding errors to cause read-overflow:
      kLinearToGammaTabS[LINEAR_TO_GAMMA_TAB_SIZE + 1] =
          kLinearToGammaTabS[LINEAR_TO_GAMMA_TAB_SIZE];
    }
    kGammaTablesSOk = 1;
  }
}

static WEBP_INLINE int Shift(int v, int shift) {
  return (shift >= 0) ? (v << shift) : (v >> -shift);
}

static WEBP_INLINE uint32_t FixedPointInterpolation(int v, uint32_t* tab,
                                                    int tab_pos_shift_right,
                                                    int tab_value_shift) {
  const uint32_t tab_pos = Shift(v, -tab_pos_shift_right);
  // fractional part, in 'tab_pos_shift' fixed-point precision
  const uint32_t x = v - (tab_pos << tab_pos_shift_right);  // fractional part
  // v0 / v1 are in kGammaToLinearBits fixed-point precision (range [0..1])
  const uint32_t v0 = Shift(tab[tab_pos + 0], tab_value_shift);
  const uint32_t v1 = Shift(tab[tab_pos + 1], tab_value_shift);
  // Final interpolation.
  const uint32_t v2 = (v1 - v0) * x;  // note: v1 >= v0.
  const int half =
      (tab_pos_shift_right > 0) ? 1 << (tab_pos_shift_right - 1) : 0;
  const uint32_t result = v0 + ((v2 + half) >> tab_pos_shift_right);
  return result;
}

static uint32_t ToLinearSrgb(uint16_t v, int bit_depth) {
  const int shift = GAMMA_TO_LINEAR_TAB_BITS - bit_depth;
  assert(v <= ((1 << bit_depth) - 1));
  if (shift >= 0) {
    // shift == 0 is a direct lookup, no need for interpolation
    return kGammaToLinearTabS[v << shift];
  }
  return FixedPointInterpolation(v, kGammaToLinearTabS, -shift, 0);
}

static uint16_t FromLinearSrgb(uint32_t value, int bit_depth) {
  assert(value <= (1 << GAMMA_TO_LINEAR_BITS));
  return FixedPointInterpolation(
      value, kLinearToGammaTabS,
      (GAMMA_TO_LINEAR_BITS - LINEAR_TO_GAMMA_TAB_BITS),
      bit_depth - GAMMA_TO_LINEAR_BITS);
}

////////////////////////////////////////////////////////////////////////////////

#define CLAMP(x, low, high) \
  (((x) < (low)) ? (low) : (((high) < (x)) ? (high) : (x)))
#define MIN(a, b) (((a) < (b)) ? (a) : (b))
#define MAX(a, b) (((a) > (b)) ? (a) : (b))

static WEBP_INLINE float Roundf(float x) {
  if (x < 0) {
    return (float)ceil((double)(x - 0.5f));
  } else {
    return (float)floor((double)(x + 0.5f));
  }
}

static WEBP_INLINE float Powf(float base, float exp) {
  return (float)pow((double)base, (double)exp);
}

static WEBP_INLINE float Log10f(float x) { return (float)log10((double)x); }

static float ToLinear709(float gamma) {
  if (gamma < 0.f) {
    return 0.f;
  } else if (gamma < 4.5f * 0.018053968510807f) {
    return gamma / 4.5f;
  } else if (gamma < 1.f) {
    return Powf((gamma + 0.09929682680944f) / 1.09929682680944f, 1.f / 0.45f);
  }
  return 1.f;
}

static float FromLinear709(float linear) {
  if (linear < 0.f) {
    return 0.f;
  } else if (linear < 0.018053968510807f) {
    return linear * 4.5f;
  } else if (linear < 1.f) {
    return 1.09929682680944f * Powf(linear, 0.45f) - 0.09929682680944f;
  }
  return 1.f;
}

static float ToLinear470M(float gamma) {
  return Powf(CLAMP(gamma, 0.f, 1.f), 2.2f);
}

static float FromLinear470M(float linear) {
  return Powf(CLAMP(linear, 0.f, 1.f), 1.f / 2.2f);
}

static float ToLinear470Bg(float gamma) {
  return Powf(CLAMP(gamma, 0.f, 1.f), 2.8f);
}

static float FromLinear470Bg(float linear) {
  return Powf(CLAMP(linear, 0.f, 1.f), 1.f / 2.8f);
}

static float ToLinearSmpte240(float gamma) {
  if (gamma < 0.f) {
    return 0.f;
  } else if (gamma < 4.f * 0.022821585529445f) {
    return gamma / 4.f;
  } else if (gamma < 1.f) {
    return Powf((gamma + 0.111572195921731f) / 1.111572195921731f, 1.f / 0.45f);
  }
  return 1.f;
}

static float FromLinearSmpte240(float linear) {
  if (linear < 0.f) {
    return 0.f;
  } else if (linear < 0.022821585529445f) {
    return linear * 4.f;
  } else if (linear < 1.f) {
    return 1.111572195921731f * Powf(linear, 0.45f) - 0.111572195921731f;
  }
  return 1.f;
}

static float ToLinearLog100(float gamma) {
  // The function is non-bijective so choose the middle of [0, 0.01].
  const float mid_interval = 0.01f / 2.f;
  return (gamma <= 0.0f) ? mid_interval
                         : Powf(10.0f, 2.f * (MIN(gamma, 1.f) - 1.0f));
}

static float FromLinearLog100(float linear) {
  return (linear < 0.01f) ? 0.0f : 1.0f + Log10f(MIN(linear, 1.f)) / 2.0f;
}

static float ToLinearLog100Sqrt10(float gamma) {
  // The function is non-bijective so choose the middle of [0, 0.00316227766f[.
  const float mid_interval = 0.00316227766f / 2.f;
  return (gamma <= 0.0f) ? mid_interval
                         : Powf(10.0f, 2.5f * (MIN(gamma, 1.f) - 1.0f));
}

static float FromLinearLog100Sqrt10(float linear) {
  return (linear < 0.00316227766f) ? 0.0f
                                   : 1.0f + Log10f(MIN(linear, 1.f)) / 2.5f;
}

static float ToLinearIec61966(float gamma) {
  if (gamma <= -4.5f * 0.018053968510807f) {
    return Powf((-gamma + 0.09929682680944f) / -1.09929682680944f, 1.f / 0.45f);
  } else if (gamma < 4.5f * 0.018053968510807f) {
    return gamma / 4.5f;
  }
  return Powf((gamma + 0.09929682680944f) / 1.09929682680944f, 1.f / 0.45f);
}

static float FromLinearIec61966(float linear) {
  if (linear <= -0.018053968510807f) {
    return -1.09929682680944f * Powf(-linear, 0.45f) + 0.09929682680944f;
  } else if (linear < 0.018053968510807f) {
    return linear * 4.5f;
  }
  return 1.09929682680944f * Powf(linear, 0.45f) - 0.09929682680944f;
}

static float ToLinearBt1361(float gamma) {
  if (gamma < -0.25f) {
    return -0.25f;
  } else if (gamma < 0.f) {
    return Powf((gamma - 0.02482420670236f) / -0.27482420670236f, 1.f / 0.45f) /
           -4.f;
  } else if (gamma < 4.5f * 0.018053968510807f) {
    return gamma / 4.5f;
  } else if (gamma < 1.f) {
    return Powf((gamma + 0.09929682680944f) / 1.09929682680944f, 1.f / 0.45f);
  }
  return 1.f;
}

static float FromLinearBt1361(float linear) {
  if (linear < -0.25f) {
    return -0.25f;
  } else if (linear < 0.f) {
    return -0.27482420670236f * Powf(-4.f * linear, 0.45f) + 0.02482420670236f;
  } else if (linear < 0.018053968510807f) {
    return linear * 4.5f;
  } else if (linear < 1.f) {
    return 1.09929682680944f * Powf(linear, 0.45f) - 0.09929682680944f;
  }
  return 1.f;
}

static float ToLinearPq(float gamma) {
  if (gamma > 0.f) {
    const float pow_gamma = Powf(gamma, 32.f / 2523.f);
    const float num = MAX(pow_gamma - 107.f / 128.f, 0.0f);
    const float den = MAX(2413.f / 128.f - 2392.f / 128.f * pow_gamma, FLT_MIN);
    return Powf(num / den, 4096.f / 653.f);
  }
  return 0.f;
}

static float FromLinearPq(float linear) {
  if (linear > 0.f) {
    const float pow_linear = Powf(linear, 653.f / 4096.f);
    const float num = 107.f / 128.f + 2413.f / 128.f * pow_linear;
    const float den = 1.0f + 2392.f / 128.f * pow_linear;
    return Powf(num / den, 2523.f / 32.f);
  }
  return 0.f;
}

static float ToLinearSmpte428(float gamma) {
  return Powf(MAX(gamma, 0.f), 2.6f) / 0.91655527974030934f;
}

static float FromLinearSmpte428(float linear) {
  return Powf(0.91655527974030934f * MAX(linear, 0.f), 1.f / 2.6f);
}

// Conversion in BT.2100 requires RGB info. Simplify to gamma correction here.
static float ToLinearHlg(float gamma) {
  if (gamma < 0.f) {
    return 0.f;
  } else if (gamma <= 0.5f) {
    return Powf((gamma * gamma) * (1.f / 3.f), 1.2f);
  }
  return Powf((expf((gamma - 0.55991073f) / 0.17883277f) + 0.28466892f) / 12.0f,
              1.2f);
}

static float FromLinearHlg(float linear) {
  linear = Powf(linear, 1.f / 1.2f);
  if (linear < 0.f) {
    return 0.f;
  } else if (linear <= (1.f / 12.f)) {
    return sqrtf(3.f * linear);
  }
  return 0.17883277f * logf(12.f * linear - 0.28466892f) + 0.55991073f;
}

uint32_t SharpYuvGammaToLinear(uint16_t v, int bit_depth,
                               SharpYuvTransferFunctionType transfer_type) {
  float v_float, linear;
  if (transfer_type == kSharpYuvTransferFunctionSrgb) {
    return ToLinearSrgb(v, bit_depth);
  }
  v_float = (float)v / ((1 << bit_depth) - 1);
  switch (transfer_type) {
    case kSharpYuvTransferFunctionBt709:
    case kSharpYuvTransferFunctionBt601:
    case kSharpYuvTransferFunctionBt2020_10Bit:
    case kSharpYuvTransferFunctionBt2020_12Bit:
      linear = ToLinear709(v_float);
      break;
    case kSharpYuvTransferFunctionBt470M:
      linear = ToLinear470M(v_float);
      break;
    case kSharpYuvTransferFunctionBt470Bg:
      linear = ToLinear470Bg(v_float);
      break;
    case kSharpYuvTransferFunctionSmpte240:
      linear = ToLinearSmpte240(v_float);
      break;
    case kSharpYuvTransferFunctionLinear:
      return v;
    case kSharpYuvTransferFunctionLog100:
      linear = ToLinearLog100(v_float);
      break;
    case kSharpYuvTransferFunctionLog100_Sqrt10:
      linear = ToLinearLog100Sqrt10(v_float);
      break;
    case kSharpYuvTransferFunctionIec61966:
      linear = ToLinearIec61966(v_float);
      break;
    case kSharpYuvTransferFunctionBt1361:
      linear = ToLinearBt1361(v_float);
      break;
    case kSharpYuvTransferFunctionSmpte2084:
      linear = ToLinearPq(v_float);
      break;
    case kSharpYuvTransferFunctionSmpte428:
      linear = ToLinearSmpte428(v_float);
      break;
    case kSharpYuvTransferFunctionHlg:
      linear = ToLinearHlg(v_float);
      break;
    default:
      assert(0);
      linear = 0;
      break;
  }
  return (uint32_t)Roundf(linear * ((1 << 16) - 1));
}

uint16_t SharpYuvLinearToGamma(uint32_t v, int bit_depth,
                               SharpYuvTransferFunctionType transfer_type) {
  float v_float, linear;
  if (transfer_type == kSharpYuvTransferFunctionSrgb) {
    return FromLinearSrgb(v, bit_depth);
  }
  v_float = (float)v / ((1 << 16) - 1);
  switch (transfer_type) {
    case kSharpYuvTransferFunctionBt709:
    case kSharpYuvTransferFunctionBt601:
    case kSharpYuvTransferFunctionBt2020_10Bit:
    case kSharpYuvTransferFunctionBt2020_12Bit:
      linear = FromLinear709(v_float);
      break;
    case kSharpYuvTransferFunctionBt470M:
      linear = FromLinear470M(v_float);
      break;
    case kSharpYuvTransferFunctionBt470Bg:
      linear = FromLinear470Bg(v_float);
      break;
    case kSharpYuvTransferFunctionSmpte240:
      linear = FromLinearSmpte240(v_float);
      break;
    case kSharpYuvTransferFunctionLinear:
      return v;
    case kSharpYuvTransferFunctionLog100:
      linear = FromLinearLog100(v_float);
      break;
    case kSharpYuvTransferFunctionLog100_Sqrt10:
      linear = FromLinearLog100Sqrt10(v_float);
      break;
    case kSharpYuvTransferFunctionIec61966:
      linear = FromLinearIec61966(v_float);
      break;
    case kSharpYuvTransferFunctionBt1361:
      linear = FromLinearBt1361(v_float);
      break;
    case kSharpYuvTransferFunctionSmpte2084:
      linear = FromLinearPq(v_float);
      break;
    case kSharpYuvTransferFunctionSmpte428:
      linear = FromLinearSmpte428(v_float);
      break;
    case kSharpYuvTransferFunctionHlg:
      linear = FromLinearHlg(v_float);
      break;
    default:
      assert(0);
      linear = 0;
      break;
  }
  return (uint16_t)Roundf(linear * ((1 << bit_depth) - 1));
}

Coverage Report

Created: 2026-08-31 06:22

Line	Count	Source
1		// Copyright 2022 Google Inc. All Rights Reserved.
2		//
3		// Use of this source code is governed by a BSD-style license
4		// that can be found in the COPYING file in the root of the source
5		// tree. An additional intellectual property rights grant can be found
6		// in the file PATENTS. All contributing project authors may
7		// be found in the AUTHORS file in the root of the source tree.
8		// -----------------------------------------------------------------------------
9		//
10		// Gamma correction utilities.
11
12		#include "./sharpyuv_gamma.h"
13
14		#include <assert.h>
15		#include <float.h>
16		#include <math.h>
17
18		#include "./sharpyuv.h"
19		#include "webp/types.h"
20
21		// Gamma correction compensates loss of resolution during chroma subsampling.
22		// Size of pre-computed table for converting from gamma to linear.
23	0	#define GAMMA_TO_LINEAR_TAB_BITS 10
24	0	#define GAMMA_TO_LINEAR_TAB_SIZE (1 << GAMMA_TO_LINEAR_TAB_BITS)
25		static uint32_t kGammaToLinearTabS[GAMMA_TO_LINEAR_TAB_SIZE + 2];
26	0	#define LINEAR_TO_GAMMA_TAB_BITS 9
27	0	#define LINEAR_TO_GAMMA_TAB_SIZE (1 << LINEAR_TO_GAMMA_TAB_BITS)
28		static uint32_t kLinearToGammaTabS[LINEAR_TO_GAMMA_TAB_SIZE + 2];
29
30		static const double kGammaF = 1. / 0.45;
31	0	#define GAMMA_TO_LINEAR_BITS 16
32
33		static volatile int kGammaTablesSOk = 0;
34	0	void SharpYuvInitGammaTables(void) {
35	0	assert(GAMMA_TO_LINEAR_BITS <= 16);
36	0	if (!kGammaTablesSOk) {
37	0	int v;
38	0	const double a = 0.09929682680944;
39	0	const double thresh = 0.018053968510807;
40	0	const double final_scale = 1 << GAMMA_TO_LINEAR_BITS;
41		// Precompute gamma to linear table.
42	0	{
43	0	const double norm = 1. / GAMMA_TO_LINEAR_TAB_SIZE;
44	0	const double a_rec = 1. / (1. + a);
45	0	for (v = 0; v <= GAMMA_TO_LINEAR_TAB_SIZE; ++v) {
46	0	const double g = norm * v;
47	0	double value;
48	0	if (g <= thresh * 4.5) {
49	0	value = g / 4.5;
50	0	} else {
51	0	value = pow(a_rec * (g + a), kGammaF);
52	0	}
53	0	kGammaToLinearTabS[v] = (uint32_t)(value * final_scale + .5);
54	0	}
55		// to prevent small rounding errors to cause read-overflow:
56	0	kGammaToLinearTabS[GAMMA_TO_LINEAR_TAB_SIZE + 1] =
57	0	kGammaToLinearTabS[GAMMA_TO_LINEAR_TAB_SIZE];
58	0	}
59		// Precompute linear to gamma table.
60	0	{
61	0	const double scale = 1. / LINEAR_TO_GAMMA_TAB_SIZE;
62	0	for (v = 0; v <= LINEAR_TO_GAMMA_TAB_SIZE; ++v) {
63	0	const double g = scale * v;
64	0	double value;
65	0	if (g <= thresh) {
66	0	value = 4.5 * g;
67	0	} else {
68	0	value = (1. + a) * pow(g, 1. / kGammaF) - a;
69	0	}
70	0	kLinearToGammaTabS[v] = (uint32_t)(final_scale * value + 0.5);
71	0	}
72		// to prevent small rounding errors to cause read-overflow:
73	0	kLinearToGammaTabS[LINEAR_TO_GAMMA_TAB_SIZE + 1] =
74	0	kLinearToGammaTabS[LINEAR_TO_GAMMA_TAB_SIZE];
75	0	}
76	0	kGammaTablesSOk = 1;
77	0	}
78	0	}
79
80	0	static WEBP_INLINE int Shift(int v, int shift) {
81	0	return (shift >= 0) ? (v << shift) : (v >> -shift);
82	0	}
83
84		static WEBP_INLINE uint32_t FixedPointInterpolation(int v, uint32_t* tab,
85		int tab_pos_shift_right,
86	0	int tab_value_shift) {
87	0	const uint32_t tab_pos = Shift(v, -tab_pos_shift_right);
88		// fractional part, in 'tab_pos_shift' fixed-point precision
89	0	const uint32_t x = v - (tab_pos << tab_pos_shift_right); // fractional part
90		// v0 / v1 are in kGammaToLinearBits fixed-point precision (range [0..1])
91	0	const uint32_t v0 = Shift(tab[tab_pos + 0], tab_value_shift);
92	0	const uint32_t v1 = Shift(tab[tab_pos + 1], tab_value_shift);
93		// Final interpolation.
94	0	const uint32_t v2 = (v1 - v0) * x; // note: v1 >= v0.
95	0	const int half =
96	0	(tab_pos_shift_right > 0) ? 1 << (tab_pos_shift_right - 1) : 0;
97	0	const uint32_t result = v0 + ((v2 + half) >> tab_pos_shift_right);
98	0	return result;
99	0	}
100
101	0	static uint32_t ToLinearSrgb(uint16_t v, int bit_depth) {
102	0	const int shift = GAMMA_TO_LINEAR_TAB_BITS - bit_depth;
103	0	assert(v <= ((1 << bit_depth) - 1));
104	0	if (shift >= 0) {
105		// shift == 0 is a direct lookup, no need for interpolation
106	0	return kGammaToLinearTabS[v << shift];
107	0	}
108	0	return FixedPointInterpolation(v, kGammaToLinearTabS, -shift, 0);
109	0	}
110
111	0	static uint16_t FromLinearSrgb(uint32_t value, int bit_depth) {
112	0	assert(value <= (1 << GAMMA_TO_LINEAR_BITS));
113	0	return FixedPointInterpolation(
114	0	value, kLinearToGammaTabS,
115	0	(GAMMA_TO_LINEAR_BITS - LINEAR_TO_GAMMA_TAB_BITS),
116	0	bit_depth - GAMMA_TO_LINEAR_BITS);
117	0	}
118
119		////////////////////////////////////////////////////////////////////////////////
120
121		#define CLAMP(x, low, high) \
122	0	(((x) < (low)) ? (low) : (((high) < (x)) ? (high) : (x)))
123	0	#define MIN(a, b) (((a) < (b)) ? (a) : (b))
124	0	#define MAX(a, b) (((a) > (b)) ? (a) : (b))
125
126	0	static WEBP_INLINE float Roundf(float x) {
127	0	if (x < 0) {
128	0	return (float)ceil((double)(x - 0.5f));
129	0	} else {
130	0	return (float)floor((double)(x + 0.5f));
131	0	}
132	0	}
133
134	0	static WEBP_INLINE float Powf(float base, float exp) {
135	0	return (float)pow((double)base, (double)exp);
136	0	}
137
138	0	static WEBP_INLINE float Log10f(float x) { return (float)log10((double)x); }
139
140	0	static float ToLinear709(float gamma) {
141	0	if (gamma < 0.f) {
142	0	return 0.f;
143	0	} else if (gamma < 4.5f * 0.018053968510807f) {
144	0	return gamma / 4.5f;
145	0	} else if (gamma < 1.f) {
146	0	return Powf((gamma + 0.09929682680944f) / 1.09929682680944f, 1.f / 0.45f);
147	0	}
148	0	return 1.f;
149	0	}
150
151	0	static float FromLinear709(float linear) {
152	0	if (linear < 0.f) {
153	0	return 0.f;
154	0	} else if (linear < 0.018053968510807f) {
155	0	return linear * 4.5f;
156	0	} else if (linear < 1.f) {
157	0	return 1.09929682680944f * Powf(linear, 0.45f) - 0.09929682680944f;
158	0	}
159	0	return 1.f;
160	0	}
161
162	0	static float ToLinear470M(float gamma) {
163	0	return Powf(CLAMP(gamma, 0.f, 1.f), 2.2f);
164	0	}
165
166	0	static float FromLinear470M(float linear) {
167	0	return Powf(CLAMP(linear, 0.f, 1.f), 1.f / 2.2f);
168	0	}
169
170	0	static float ToLinear470Bg(float gamma) {
171	0	return Powf(CLAMP(gamma, 0.f, 1.f), 2.8f);
172	0	}
173
174	0	static float FromLinear470Bg(float linear) {
175	0	return Powf(CLAMP(linear, 0.f, 1.f), 1.f / 2.8f);
176	0	}
177
178	0	static float ToLinearSmpte240(float gamma) {
179	0	if (gamma < 0.f) {
180	0	return 0.f;
181	0	} else if (gamma < 4.f * 0.022821585529445f) {
182	0	return gamma / 4.f;
183	0	} else if (gamma < 1.f) {
184	0	return Powf((gamma + 0.111572195921731f) / 1.111572195921731f, 1.f / 0.45f);
185	0	}
186	0	return 1.f;
187	0	}
188
189	0	static float FromLinearSmpte240(float linear) {
190	0	if (linear < 0.f) {
191	0	return 0.f;
192	0	} else if (linear < 0.022821585529445f) {
193	0	return linear * 4.f;
194	0	} else if (linear < 1.f) {
195	0	return 1.111572195921731f * Powf(linear, 0.45f) - 0.111572195921731f;
196	0	}
197	0	return 1.f;
198	0	}
199
200	0	static float ToLinearLog100(float gamma) {
201		// The function is non-bijective so choose the middle of [0, 0.01].
202	0	const float mid_interval = 0.01f / 2.f;
203	0	return (gamma <= 0.0f) ? mid_interval
204	0	: Powf(10.0f, 2.f * (MIN(gamma, 1.f) - 1.0f));
205	0	}
206
207	0	static float FromLinearLog100(float linear) {
208	0	return (linear < 0.01f) ? 0.0f : 1.0f + Log10f(MIN(linear, 1.f)) / 2.0f;
209	0	}
210
211	0	static float ToLinearLog100Sqrt10(float gamma) {
212		// The function is non-bijective so choose the middle of [0, 0.00316227766f[.
213	0	const float mid_interval = 0.00316227766f / 2.f;
214	0	return (gamma <= 0.0f) ? mid_interval
215	0	: Powf(10.0f, 2.5f * (MIN(gamma, 1.f) - 1.0f));
216	0	}
217
218	0	static float FromLinearLog100Sqrt10(float linear) {
219	0	return (linear < 0.00316227766f) ? 0.0f
220	0	: 1.0f + Log10f(MIN(linear, 1.f)) / 2.5f;
221	0	}
222
223	0	static float ToLinearIec61966(float gamma) {
224	0	if (gamma <= -4.5f * 0.018053968510807f) {
225	0	return Powf((-gamma + 0.09929682680944f) / -1.09929682680944f, 1.f / 0.45f);
226	0	} else if (gamma < 4.5f * 0.018053968510807f) {
227	0	return gamma / 4.5f;
228	0	}
229	0	return Powf((gamma + 0.09929682680944f) / 1.09929682680944f, 1.f / 0.45f);
230	0	}
231
232	0	static float FromLinearIec61966(float linear) {
233	0	if (linear <= -0.018053968510807f) {
234	0	return -1.09929682680944f * Powf(-linear, 0.45f) + 0.09929682680944f;
235	0	} else if (linear < 0.018053968510807f) {
236	0	return linear * 4.5f;
237	0	}
238	0	return 1.09929682680944f * Powf(linear, 0.45f) - 0.09929682680944f;
239	0	}
240
241	0	static float ToLinearBt1361(float gamma) {
242	0	if (gamma < -0.25f) {
243	0	return -0.25f;
244	0	} else if (gamma < 0.f) {
245	0	return Powf((gamma - 0.02482420670236f) / -0.27482420670236f, 1.f / 0.45f) /
246	0	-4.f;
247	0	} else if (gamma < 4.5f * 0.018053968510807f) {
248	0	return gamma / 4.5f;
249	0	} else if (gamma < 1.f) {
250	0	return Powf((gamma + 0.09929682680944f) / 1.09929682680944f, 1.f / 0.45f);
251	0	}
252	0	return 1.f;
253	0	}
254
255	0	static float FromLinearBt1361(float linear) {
256	0	if (linear < -0.25f) {
257	0	return -0.25f;
258	0	} else if (linear < 0.f) {
259	0	return -0.27482420670236f * Powf(-4.f * linear, 0.45f) + 0.02482420670236f;
260	0	} else if (linear < 0.018053968510807f) {
261	0	return linear * 4.5f;
262	0	} else if (linear < 1.f) {
263	0	return 1.09929682680944f * Powf(linear, 0.45f) - 0.09929682680944f;
264	0	}
265	0	return 1.f;
266	0	}
267
268	0	static float ToLinearPq(float gamma) {
269	0	if (gamma > 0.f) {
270	0	const float pow_gamma = Powf(gamma, 32.f / 2523.f);
271	0	const float num = MAX(pow_gamma - 107.f / 128.f, 0.0f);
272	0	const float den = MAX(2413.f / 128.f - 2392.f / 128.f * pow_gamma, FLT_MIN);
273	0	return Powf(num / den, 4096.f / 653.f);
274	0	}
275	0	return 0.f;
276	0	}
277
278	0	static float FromLinearPq(float linear) {
279	0	if (linear > 0.f) {
280	0	const float pow_linear = Powf(linear, 653.f / 4096.f);
281	0	const float num = 107.f / 128.f + 2413.f / 128.f * pow_linear;
282	0	const float den = 1.0f + 2392.f / 128.f * pow_linear;
283	0	return Powf(num / den, 2523.f / 32.f);
284	0	}
285	0	return 0.f;
286	0	}
287
288	0	static float ToLinearSmpte428(float gamma) {
289	0	return Powf(MAX(gamma, 0.f), 2.6f) / 0.91655527974030934f;
290	0	}
291
292	0	static float FromLinearSmpte428(float linear) {
293	0	return Powf(0.91655527974030934f * MAX(linear, 0.f), 1.f / 2.6f);
294	0	}
295
296		// Conversion in BT.2100 requires RGB info. Simplify to gamma correction here.
297	0	static float ToLinearHlg(float gamma) {
298	0	if (gamma < 0.f) {
299	0	return 0.f;
300	0	} else if (gamma <= 0.5f) {
301	0	return Powf((gamma * gamma) * (1.f / 3.f), 1.2f);
302	0	}
303	0	return Powf((expf((gamma - 0.55991073f) / 0.17883277f) + 0.28466892f) / 12.0f,
304	0	1.2f);
305	0	}
306
307	0	static float FromLinearHlg(float linear) {
308	0	linear = Powf(linear, 1.f / 1.2f);
309	0	if (linear < 0.f) {
310	0	return 0.f;
311	0	} else if (linear <= (1.f / 12.f)) {
312	0	return sqrtf(3.f * linear);
313	0	}
314	0	return 0.17883277f * logf(12.f * linear - 0.28466892f) + 0.55991073f;
315	0	}
316
317		uint32_t SharpYuvGammaToLinear(uint16_t v, int bit_depth,
318	0	SharpYuvTransferFunctionType transfer_type) {
319	0	float v_float, linear;
320	0	if (transfer_type == kSharpYuvTransferFunctionSrgb) {
321	0	return ToLinearSrgb(v, bit_depth);
322	0	}
323	0	v_float = (float)v / ((1 << bit_depth) - 1);
324	0	switch (transfer_type) {
325	0	case kSharpYuvTransferFunctionBt709:
326	0	case kSharpYuvTransferFunctionBt601:
327	0	case kSharpYuvTransferFunctionBt2020_10Bit:
328	0	case kSharpYuvTransferFunctionBt2020_12Bit:
329	0	linear = ToLinear709(v_float);
330	0	break;
331	0	case kSharpYuvTransferFunctionBt470M:
332	0	linear = ToLinear470M(v_float);
333	0	break;
334	0	case kSharpYuvTransferFunctionBt470Bg:
335	0	linear = ToLinear470Bg(v_float);
336	0	break;
337	0	case kSharpYuvTransferFunctionSmpte240:
338	0	linear = ToLinearSmpte240(v_float);
339	0	break;
340	0	case kSharpYuvTransferFunctionLinear:
341	0	return v;
342	0	case kSharpYuvTransferFunctionLog100:
343	0	linear = ToLinearLog100(v_float);
344	0	break;
345	0	case kSharpYuvTransferFunctionLog100_Sqrt10:
346	0	linear = ToLinearLog100Sqrt10(v_float);
347	0	break;
348	0	case kSharpYuvTransferFunctionIec61966:
349	0	linear = ToLinearIec61966(v_float);
350	0	break;
351	0	case kSharpYuvTransferFunctionBt1361:
352	0	linear = ToLinearBt1361(v_float);
353	0	break;
354	0	case kSharpYuvTransferFunctionSmpte2084:
355	0	linear = ToLinearPq(v_float);
356	0	break;
357	0	case kSharpYuvTransferFunctionSmpte428:
358	0	linear = ToLinearSmpte428(v_float);
359	0	break;
360	0	case kSharpYuvTransferFunctionHlg:
361	0	linear = ToLinearHlg(v_float);
362	0	break;
363	0	default:
364	0	assert(0);
365	0	linear = 0;
366	0	break;
367	0	}
368	0	return (uint32_t)Roundf(linear * ((1 << 16) - 1));
369	0	}
370
371		uint16_t SharpYuvLinearToGamma(uint32_t v, int bit_depth,
372	0	SharpYuvTransferFunctionType transfer_type) {
373	0	float v_float, linear;
374	0	if (transfer_type == kSharpYuvTransferFunctionSrgb) {
375	0	return FromLinearSrgb(v, bit_depth);
376	0	}
377	0	v_float = (float)v / ((1 << 16) - 1);
378	0	switch (transfer_type) {
379	0	case kSharpYuvTransferFunctionBt709:
380	0	case kSharpYuvTransferFunctionBt601:
381	0	case kSharpYuvTransferFunctionBt2020_10Bit:
382	0	case kSharpYuvTransferFunctionBt2020_12Bit:
383	0	linear = FromLinear709(v_float);
384	0	break;
385	0	case kSharpYuvTransferFunctionBt470M:
386	0	linear = FromLinear470M(v_float);
387	0	break;
388	0	case kSharpYuvTransferFunctionBt470Bg:
389	0	linear = FromLinear470Bg(v_float);
390	0	break;
391	0	case kSharpYuvTransferFunctionSmpte240:
392	0	linear = FromLinearSmpte240(v_float);
393	0	break;
394	0	case kSharpYuvTransferFunctionLinear:
395	0	return v;
396	0	case kSharpYuvTransferFunctionLog100:
397	0	linear = FromLinearLog100(v_float);
398	0	break;
399	0	case kSharpYuvTransferFunctionLog100_Sqrt10:
400	0	linear = FromLinearLog100Sqrt10(v_float);
401	0	break;
402	0	case kSharpYuvTransferFunctionIec61966:
403	0	linear = FromLinearIec61966(v_float);
404	0	break;
405	0	case kSharpYuvTransferFunctionBt1361:
406	0	linear = FromLinearBt1361(v_float);
407	0	break;
408	0	case kSharpYuvTransferFunctionSmpte2084:
409	0	linear = FromLinearPq(v_float);
410	0	break;
411	0	case kSharpYuvTransferFunctionSmpte428:
412	0	linear = FromLinearSmpte428(v_float);
413	0	break;
414	0	case kSharpYuvTransferFunctionHlg:
415	0	linear = FromLinearHlg(v_float);
416	0	break;
417	0	default:
418	0	assert(0);
419	0	linear = 0;
420	0	break;
421	0	}
422	0	return (uint16_t)Roundf(linear * ((1 << bit_depth) - 1));
423	0	}