chroma-js/src/io/lab/lab-constants.js

JavaScript library for color conversions

const labConstants = {
    // Corresponds roughly to RGB brighter/darker
    Kn: 18,

    // D65 standard referent
    labWhitePoint: 'd65',
    Xn: 0.95047,
    Yn: 1,
    Zn: 1.08883,

    t0: 0.137931034, // 4 / 29
    t1: 0.206896552, // 6 / 29
    t2: 0.12841855, // 3 * t1 * t1
    t3: 0.008856452, // t1 * t1 * t1,

    kE: 216.0 / 24389.0,
    kKE: 8.0,
    kK: 24389.0 / 27.0,

    RefWhiteRGB: {
        // sRGB
        X: 0.95047,
        Y: 1,
        Z: 1.08883
    },

    MtxRGB2XYZ: {
        m00: 0.4124564390896922,
        m01: 0.21267285140562253,
        m02: 0.0193338955823293,
        m10: 0.357576077643909,
        m11: 0.715152155287818,
        m12: 0.11919202588130297,
        m20: 0.18043748326639894,
        m21: 0.07217499330655958,
        m22: 0.9503040785363679
    },

    MtxXYZ2RGB: {
        m00: 3.2404541621141045,
        m01: -0.9692660305051868,
        m02: 0.055643430959114726,
        m10: -1.5371385127977166,
        m11: 1.8760108454466942,
        m12: -0.2040259135167538,
        m20: -0.498531409556016,
        m21: 0.041556017530349834,
        m22: 1.0572251882231791
    },

    // used in rgb2xyz
    As: 0.9414285350000001,
    Bs: 1.040417467,
    Cs: 1.089532651,

    MtxAdaptMa: {
        m00: 0.8951,
        m01: -0.7502,
        m02: 0.0389,
        m10: 0.2664,
        m11: 1.7135,
        m12: -0.0685,
        m20: -0.1614,
        m21: 0.0367,
        m22: 1.0296
    },

    MtxAdaptMaI: {
        m00: 0.9869929054667123,
        m01: 0.43230526972339456,
        m02: -0.008528664575177328,
        m10: -0.14705425642099013,
        m11: 0.5183602715367776,
        m12: 0.04004282165408487,
        m20: 0.15996265166373125,
        m21: 0.0492912282128556,
        m22: 0.9684866957875502
    }
};

export default labConstants;

// taken from https://de.mathworks.com/help/images/ref/whitepoint.html
const ILLUMINANTS = new Map([
    // ASTM E308-01
    ['a', [1.0985, 0.35585]],
    // Wyszecki & Stiles, p. 769
    ['b', [1.0985, 0.35585]],
    // C ASTM E308-01
    ['c', [0.98074, 1.18232]],
    // D50 (ASTM E308-01)
    ['d50', [0.96422, 0.82521]],
    // D55 (ASTM E308-01)
    ['d55', [0.95682, 0.92149]],
    // D65 (ASTM E308-01)
    ['d65', [0.95047, 1.08883]],
    // E (ASTM E308-01)
    ['e', [1, 1, 1]],
    // F2 (ASTM E308-01)
    ['f2', [0.99186, 0.67393]],
    // F7 (ASTM E308-01)
    ['f7', [0.95041, 1.08747]],
    // F11 (ASTM E308-01)
    ['f11', [1.00962, 0.6435]],
    ['icc', [0.96422, 0.82521]]
]);

export function setLabWhitePoint(name) {
    const ill = ILLUMINANTS.get(String(name).toLowerCase());
    if (!ill) {
        throw new Error('unknown Lab illuminant ' + name);
    }
    labConstants.labWhitePoint = name;
    labConstants.Xn = ill[0];
    labConstants.Zn = ill[1];
}

export function getLabWhitePoint() {
    return labConstants.labWhitePoint;
}