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color_helpers: Update color math
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@jeremyselan @misyltoad
jeremyselan authored and misyltoad committed Apr 20, 2023
1 parent 5ce316f commit ef41d9f
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Showing 2 changed files with 33 additions and 37 deletions.
64 changes: 29 additions & 35 deletions src/color_helpers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -215,10 +215,11 @@ void calcColorTransform( uint16_t * pRgbxData1d, int nLutSize1d,
glm::mat3 xyz_from_dest = normalised_primary_matrix( dest.primaries, dest.white, 1.f );
glm::mat3 dest_from_xyz = glm::inverse( xyz_from_dest );
glm::mat3 xyz_from_source = normalised_primary_matrix( source.primaries, source.white, 1.f );
// TODO: include color adaptation matrix if white point conversion is needed
glm::mat3 dest_from_source = dest_from_xyz * xyz_from_source;
glm::mat3 dest_from_source = dest_from_xyz * xyz_from_source; // Absolute colorimetric mapping

// Generate shaper lut (for now, identity)
// TODO: if source EOTF doest match dest EOTF, generate a proper shaper lut (and the inverse)
// and then compute a shaper-aware 3DLUT
if ( pRgbxData1d )
{
float flScale = 1.f / ( (float) nLutSize1d - 1.f );
Expand All @@ -236,13 +237,13 @@ void calcColorTransform( uint16_t * pRgbxData1d, int nLutSize1d,

if ( pRgbxData3d )
{
int nOutOfGamut = 0;
float flScale = 1.f / ( (float) nLutEdgeSize3d - 1.f );

// Precalc night mode scalars
// amount and saturation are overdetermined but we separate the two as they conceptually represent
// different quantities, and this preserves forwards algorithmic compatibility
glm::vec3 nightModeMultHSV( nightmode.hue, clamp01( nightmode.saturation * nightmode.amount ), 1.f );
glm::vec3 vNightModeGammaMult = hsv_to_rgb( nightModeMultHSV );
glm::vec3 vNightModeMultLinear = glm::pow( hsv_to_rgb( nightModeMultHSV ), glm::vec3( 2.2f ) );

for ( int nBlue=0; nBlue<nLutEdgeSize3d; ++nBlue )
{
Expand All @@ -266,18 +267,17 @@ void calcColorTransform( uint16_t * pRgbxData1d, int nLutSize1d,
// Convert to dest colorimetry (linearized display referred)
glm::vec3 destColorLinear = dest_from_source * sourceColorLinear;

// Do a naieve blending with native gamut based on saturation
// Do a naive blending with native gamut based on saturation
// ( A very simplified form of gamut mapping )
glm::vec3 hsvColor = rgb_to_hsv( sourceColor );
float amount = cfit( hsvColor.y, mapping.blendEnableMinSat, mapping.blendEnableMaxSat, mapping.blendAmountMin, mapping.blendAmountMax );
// float colorSaturation = rgb_to_hsv( sourceColor ).y;
float colorSaturation = rgb_to_hsv( sourceColorLinear ).y;
float amount = cfit( colorSaturation, mapping.blendEnableMinSat, mapping.blendEnableMaxSat, mapping.blendAmountMin, mapping.blendAmountMax );
destColorLinear = glm::mix( destColorLinear, sourceColorLinear, amount );

if ( BOutOfGamut( destColorLinear ) )
{
nOutOfGamut += 1;
}
// Apply night mode
destColorLinear = vNightModeMultLinear * destColorLinear;

// Apply output gamma
// Apply dest EOTF
destColorLinear = glm::clamp( destColorLinear, glm::vec3( 0.f ), glm::vec3( 1.f ) );
glm::vec3 destColor;
if ( dest.eotf == EOTF::Gamma22 )
Expand All @@ -289,10 +289,7 @@ void calcColorTransform( uint16_t * pRgbxData1d, int nLutSize1d,
destColor = destColorLinear;
}

// Apply night mode
destColor = vNightModeGammaMult * destColor;

// Save in output LUT
// Write LUT
int nLutIndex = nBlue * nLutEdgeSize3d * nLutEdgeSize3d + nGreen * nLutEdgeSize3d + nRed;
pRgbxData3d[nLutIndex * 4 + 0] = drm_quantize_lut_value( destColor.x );
pRgbxData3d[nLutIndex * 4 + 1] = drm_quantize_lut_value( destColor.y );
Expand All @@ -311,39 +308,36 @@ void generateSyntheticInputColorimetry( displaycolorimetry_t * pSynetheticInputC
// Generic narrow gamut display (709) --> COLOR 0.5
// Generic wide gamut display --> COLOR 1.0

displaycolorimetry_t narrowGamutGeneric;
narrowGamutGeneric.primaries = { { 0.64f, 0.33f }, { 0.30f, 0.60f }, { 0.15f, 0.06f } }; // BT.709
narrowGamutGeneric.white = { 0.3127f, 0.3290f }; // D65
narrowGamutGeneric.eotf = EOTF::Gamma22;

displaycolorimetry_t wideGamutGeneric;
wideGamutGeneric.primaries = { { 0.6825f, 0.3165f }, { 0.241f, 0.719f }, { 0.138f, 0.050f } };
wideGamutGeneric.white = { 0.3127f, 0.3290f }; // D65
wideGamutGeneric.eotf = EOTF::Gamma22;

colormapping_t mappingWideGamut;
mappingWideGamut.blendEnableMinSat = 0.75f;
mappingWideGamut.blendEnableMaxSat = 1.0f;
mappingWideGamut.blendAmountMin = 0.0f;
mappingWideGamut.blendAmountMax = 0.5f;
// Assume linear saturation computation
colormapping_t mapSmoothToCubeLinearSat;
mapSmoothToCubeLinearSat.blendEnableMinSat = 0.7f;
mapSmoothToCubeLinearSat.blendEnableMaxSat = 1.0f;
mapSmoothToCubeLinearSat.blendAmountMin = 0.0f;
mapSmoothToCubeLinearSat.blendAmountMax = 1.f;

colormapping_t mappingNone;
mappingNone.blendEnableMinSat = 0.65f;
mappingNone.blendEnableMaxSat = 0.90f;
mappingNone.blendAmountMin = 0.0f;
mappingNone.blendAmountMax = 0.0f;
// Assume linear saturation computation
colormapping_t mapPartialToCubeLinearSat;
mapPartialToCubeLinearSat.blendEnableMinSat = 0.7f;
mapPartialToCubeLinearSat.blendEnableMaxSat = 1.0f;
mapPartialToCubeLinearSat.blendAmountMin = 0.0f;
mapPartialToCubeLinearSat.blendAmountMax = 0.25;

if ( flSDRGamutWideness < 0.5f )
{
float t = cfit( flSDRGamutWideness, 0.f, 0.5f, 0.0f, 1.0f );
*pSynetheticInputColorimetry = lerp( nativeDisplayOutput, narrowGamutGeneric, t );
*pSyntheticColorMapping = mappingNone;
*pSynetheticInputColorimetry = lerp( nativeDisplayOutput, wideGamutGeneric, t );
*pSyntheticColorMapping = mapSmoothToCubeLinearSat;
}
else
{
float t = cfit( flSDRGamutWideness, 0.5f, 1.0f, 0.0f, 1.0f );
*pSynetheticInputColorimetry = lerp( narrowGamutGeneric, wideGamutGeneric, t );
*pSyntheticColorMapping = lerp( mappingNone, mappingWideGamut, t );
*pSynetheticInputColorimetry = wideGamutGeneric;
*pSyntheticColorMapping = lerp( mapSmoothToCubeLinearSat, mapPartialToCubeLinearSat, t );
}
}

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6 changes: 4 additions & 2 deletions src/color_helpers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -117,6 +117,8 @@ colormapping_t lerp( const colormapping_t & a, const colormapping_t & b, float t
// I.e., for a shaper lut with 256 input colors nLutSize1d = 256, countof(pRgbxData1d) = 1024
// nLutEdgeSize3d is the number of color entries, per edge, in the 3d lut
// I.e., for a 17x17x17 lut nLutEdgeSize3d = 17, countof(pRgbxData3d) = 19652
//
// If the white points differ, this performs an absolute colorimetric match

void calcColorTransform( uint16_t * pRgbxData1d, int nLutSize1d,
uint16_t * pRgbxData3d, int nLutEdgeSize3d,
Expand Down Expand Up @@ -177,14 +179,14 @@ nits_to_u16_dark(float nits)

static constexpr displaycolorimetry_t displaycolorimetry_709_gamma22
{
.primaries = { { 0.64f, 0.33f }, { 0.30f, 0.60f }, { 0.15f, 0.06f } }, // BT.709
.primaries = { { 0.64f, 0.33f }, { 0.30f, 0.60f }, { 0.15f, 0.06f } },
.white = { 0.3127f, 0.3290f }, // D65
.eotf = EOTF::Gamma22,
};

static constexpr displaycolorimetry_t displaycolorimetry_2020_pq
{
.primaries = { { 0.708f, 0.292f }, { 0.170f, 0.797f }, { 0.131f, 0.046f } }, // BT.709
.primaries = { { 0.708f, 0.292f }, { 0.170f, 0.797f }, { 0.131f, 0.046f } },
.white = { 0.3127f, 0.3290f }, // D65
.eotf = EOTF::PQ,
};
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