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180 lines (163 loc) · 6.48 KB
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package color
import "fmt"
var (
Bradford = &CAT{
ToCone: [3][3]float64{
{+0.8951, +0.2664, -0.1614},
{-0.7502, +1.7135, +0.0367},
{+0.0389, -0.0685, +1.0296},
},
FromCone: [3][3]float64{
{0.9869929054667121, -0.14705425642099013, 0.15996265166373122},
{0.4323052697233945, 0.5183602715367774, 0.049291228212855594},
{-0.00852866457517732, 0.04004282165408486, 0.96848669578755},
},
}
CAT16 = &CAT{
ToCone: [3][3]float64{
{0.401288, 0.650173, -0.051461},
{-0.250268, 1.204414, 0.045854},
{-0.002079, 0.048952, 0.953127},
},
FromCone: [3][3]float64{
{1.862067855087233, -1.0112546305316845, 0.14918677544445172},
{0.3875265432361372, 0.6214474419314753, -0.008973985167612521},
{-0.01584149884933386, -0.03412293802851557, 1.0499644368778496},
},
}
)
var (
// Standard illuminants for the CIE 1931 standard observer, from tables T.3,
// T.8, T.8.2, and T.9 in CIE 15:2004.
WhitesCIE2004TwoDegA = Chromaticity{0.44758, 040745}
WhitesCIE2004TwoDegC = Chromaticity{0.31006, 0.31616}
WhitesCIE2004TwoDegD50 = Chromaticity{0.34567, 0.35851}
WhitesCIE2004TwoDegD55 = Chromaticity{0.33243, 0.34744}
WhitesCIE2004TwoDegD65 = Chromaticity{0.31272, 0.32903}
WhitesCIE2004TwoDegD75 = Chromaticity{0.29903, 0.31488}
WhitesCIE2004TwoDegFL1 = Chromaticity{0.3131, 0.3371}
WhitesCIE2004TwoDegFL2 = Chromaticity{0.3721, 0.3751}
WhitesCIE2004TwoDegFL3 = Chromaticity{0.4091, 0.3941}
WhitesCIE2004TwoDegFL3_1 = Chromaticity{0.4407, 0.4033}
WhitesCIE2004TwoDegFL3_2 = Chromaticity{0.3808, 0.3734}
WhitesCIE2004TwoDegFL3_3 = Chromaticity{0.3153, 0.3439}
WhitesCIE2004TwoDegFL3_4 = Chromaticity{0.4429, 0.4043}
WhitesCIE2004TwoDegFL3_5 = Chromaticity{0.3749, 0.3672}
WhitesCIE2004TwoDegFL3_6 = Chromaticity{0.3488, 0.36}
WhitesCIE2004TwoDegFL3_7 = Chromaticity{0.4384, 0.4045}
WhitesCIE2004TwoDegFL3_8 = Chromaticity{0.382, 0.3832}
WhitesCIE2004TwoDegFL3_9 = Chromaticity{0.3499, 0.3591}
WhitesCIE2004TwoDegFL3_10 = Chromaticity{0.3455, 0.356}
WhitesCIE2004TwoDegFL3_11 = Chromaticity{0.3245, 0.3434}
WhitesCIE2004TwoDegFL3_12 = Chromaticity{0.4377, 0.4037}
WhitesCIE2004TwoDegFL3_13 = Chromaticity{0.383, 0.3724}
WhitesCIE2004TwoDegFL3_14 = Chromaticity{0.3447, 0.3609}
WhitesCIE2004TwoDegFL3_15 = Chromaticity{0.3127, 0.3288}
WhitesCIE2004TwoDegFL4 = Chromaticity{0.4402, 0.4031}
WhitesCIE2004TwoDegFL5 = Chromaticity{0.3138, 0.3452}
WhitesCIE2004TwoDegFL6 = Chromaticity{0.3779, 0.3882}
WhitesCIE2004TwoDegFL7 = Chromaticity{0.3129, 0.3292}
WhitesCIE2004TwoDegFL8 = Chromaticity{0.3458, 0.3586}
WhitesCIE2004TwoDegFL9 = Chromaticity{0.3741, 0.3727}
WhitesCIE2004TwoDegFL10 = Chromaticity{0.3458, 0.3588}
WhitesCIE2004TwoDegFL11 = Chromaticity{0.3805, 0.3769}
WhitesCIE2004TwoDegFL12 = Chromaticity{0.4370, 0.4042}
WhitesCIE2004TwoDegHP1 = Chromaticity{0.533, 0.415}
WhitesCIE2004TwoDegHP2 = Chromaticity{0.4778, 0.4158}
WhitesCIE2004TwoDegHP3 = Chromaticity{0.4302, 0.4075}
WhitesCIE2004TwoDegHP4 = Chromaticity{0.3812, 0.3797}
WhitesCIE2004TwoDegHP5 = Chromaticity{0.3776, 0.3713}
// Standard illuminants for the CIE 1964 standard observer, from table T.3
// in CIE 15:2004.
WhitesCIE2004TenDegA = Chromaticity{0.45117, 0.40594}
WhitesCIE2004TenDegC = Chromaticity{0.31039, 0.31905}
WhitesCIE2004TenDegD50 = Chromaticity{0.34773, 0.35952}
WhitesCIE2004TenDegD55 = Chromaticity{0.33412, 0.34877}
WhitesCIE2004TenDegD65 = Chromaticity{0.31381, 0.33098}
WhitesCIE2004TenDegD75 = Chromaticity{0.29968, 0.31740}
// The D50 white point as defined in [CSS Color Module Level 4]. This
// corresponds to [WhitesCIE2004TwoDegD50] but rounded to 4 digits.
//
// [CSS Color Module Level 4]: https://www.w3.org/TR/css-color-4/
WhitesCSSD50 = Chromaticity{0.3457, 0.3585}
// The D65 white point as specified by sRGB. This corresponds to
// [WhitesCIE2004TwoDegD65] but rounded to 4 digits.
WhitesSRGBD65 = Chromaticity{0.3127, 0.3290}
)
// MakeCIEDaylightIlluminant computes a daylight illuminant at a nominal
// correlated color temperature. The illuminant's correlated color temperature
// will be approximately equal to the nominal value, but not exactly so.
//
// Note that due to pecularities in rounding in the CIE standards, values
// returned by this function will not exactly match predefined daylight
// illuminants.
//
// The color temperature, specified in Kelvin, must be between 4000 K and
// 25,000 K.
func MakeCIEDaylightIlluminant(temp float64) Chromaticity {
switch {
case temp < 4000, temp > 25_000:
fallthrough
default:
// function not defined for this range
panic(fmt.Sprintf("color temperature %v is not in range [4000, 25000]", temp))
case temp <= 7000:
// Formula taken from CIE 15:2004, page 3, equations 3.2 and 3.3.
x := (-4.6070e9)/(temp*temp*temp) + 2.9678e6/(temp*temp) + 0.09911e3/temp + 0.244063
y := -3*x*x + 2.870*x - 0.275
return Chromaticity{x, y}
case temp <= 25_000:
// Formula taken from CIE 15:2004, pages 3-4, equations 3.2 and 3.4.
x := (-2.0064e9)/(temp*temp*temp) + 1.9018e6/(temp*temp) + 0.24748e3/temp + 0.237040
y := -3*x*x + 2.870*x - 0.275
return Chromaticity{x, y}
}
}
// CAT represents a chromatic adaptation transform. It consists of two matrices,
// one for converting from XYZ to cone responses and one for converting from
// cone responses back to XYZ.
//
// Given a CAT, colors can be adapted between any two white points, either by
// using [CAT.Adapt] for one-offs, or by combining [CAT.Matrix] and [Adapt],
// which allows reusing matrices computed for pairs of white points.
type CAT struct {
ToCone [3][3]float64
FromCone [3][3]float64
}
func (cat *CAT) Adapt(xyz *[3]float64, src, dst Chromaticity) [3]float64 {
m := cat.Matrix(src, dst)
return Adapt(xyz, &m)
}
func (cat *CAT) Matrix(src, dst Chromaticity) [3][3]float64 {
ws := src.XYZ()
wd := dst.XYZ()
coneS := mulVecMat(&ws, &cat.ToCone)
coneD := mulVecMat(&wd, &cat.ToCone)
ρS := coneS[0]
γS := coneS[1]
βS := coneS[2]
ρD := coneD[0]
γD := coneD[1]
βD := coneD[2]
a := cat.FromCone[0][0]
b := cat.FromCone[0][1]
c := cat.FromCone[0][2]
d := cat.FromCone[1][0]
e := cat.FromCone[1][1]
f := cat.FromCone[1][2]
g := cat.FromCone[2][0]
h := cat.FromCone[2][1]
i := cat.FromCone[2][2]
rρ := ρD / ρS
rγ := γD / γS
rβ := βD / βS
m_ := [3][3]float64{
{a * rρ, b * rγ, c * rβ},
{d * rρ, e * rγ, f * rβ},
{g * rρ, h * rγ, i * rβ},
}
return mulMatMat(&m_, &cat.ToCone)
}
func Adapt(xyz *[3]float64, m *[3][3]float64) [3]float64 {
return mulVecMat(xyz, m)
}