chroma-js/src/io/lab/lab2rgb.js

JavaScript library for color conversions

import LAB_CONSTANTS from './lab-constants.js';
import { unpack } from '../../utils/index.js';

/*
 * L* [0..100]
 * a [-100..100]
 * b [-100..100]
 */
const lab2rgb = (...args) => {
    args = unpack(args, 'lab');
    const [L, a, b] = args;
    const [x, y, z] = lab2xyz(L, a, b);
    const [r, g, b_] = xyz2rgb(x, y, z);
    return [r, g, b_, args.length > 3 ? args[3] : 1];
};

const lab2xyz = (L, a, b) => {
    const { kE, kK, kKE, Xn, Yn, Zn } = LAB_CONSTANTS;

    const fy = (L + 16.0) / 116.0;
    const fx = 0.002 * a + fy;
    const fz = fy - 0.005 * b;

    const fx3 = fx * fx * fx;
    const fz3 = fz * fz * fz;

    const xr = fx3 > kE ? fx3 : (116.0 * fx - 16.0) / kK;
    const yr = L > kKE ? Math.pow((L + 16.0) / 116.0, 3.0) : L / kK;
    const zr = fz3 > kE ? fz3 : (116.0 * fz - 16.0) / kK;

    const x = xr * Xn;
    const y = yr * Yn;
    const z = zr * Zn;

    return [x, y, z];
};

const compand = (linear) => {
    /* sRGB */
    const sign = Math.sign(linear);
    linear = Math.abs(linear);
    return (
        (linear <= 0.0031308
            ? linear * 12.92
            : 1.055 * Math.pow(linear, 1.0 / 2.4) - 0.055) * sign
    );
};

const xyz2rgb = (x, y, z) => {
    const { MtxAdaptMa, MtxAdaptMaI, MtxXYZ2RGB, RefWhiteRGB, Xn, Yn, Zn } =
        LAB_CONSTANTS;

    const As = Xn * MtxAdaptMa.m00 + Yn * MtxAdaptMa.m10 + Zn * MtxAdaptMa.m20;
    const Bs = Xn * MtxAdaptMa.m01 + Yn * MtxAdaptMa.m11 + Zn * MtxAdaptMa.m21;
    const Cs = Xn * MtxAdaptMa.m02 + Yn * MtxAdaptMa.m12 + Zn * MtxAdaptMa.m22;

    const Ad =
        RefWhiteRGB.X * MtxAdaptMa.m00 +
        RefWhiteRGB.Y * MtxAdaptMa.m10 +
        RefWhiteRGB.Z * MtxAdaptMa.m20;
    const Bd =
        RefWhiteRGB.X * MtxAdaptMa.m01 +
        RefWhiteRGB.Y * MtxAdaptMa.m11 +
        RefWhiteRGB.Z * MtxAdaptMa.m21;
    const Cd =
        RefWhiteRGB.X * MtxAdaptMa.m02 +
        RefWhiteRGB.Y * MtxAdaptMa.m12 +
        RefWhiteRGB.Z * MtxAdaptMa.m22;

    const X1 =
        (x * MtxAdaptMa.m00 + y * MtxAdaptMa.m10 + z * MtxAdaptMa.m20) *
        (Ad / As);
    const Y1 =
        (x * MtxAdaptMa.m01 + y * MtxAdaptMa.m11 + z * MtxAdaptMa.m21) *
        (Bd / Bs);
    const Z1 =
        (x * MtxAdaptMa.m02 + y * MtxAdaptMa.m12 + z * MtxAdaptMa.m22) *
        (Cd / Cs);

    const X2 =
        X1 * MtxAdaptMaI.m00 + Y1 * MtxAdaptMaI.m10 + Z1 * MtxAdaptMaI.m20;
    const Y2 =
        X1 * MtxAdaptMaI.m01 + Y1 * MtxAdaptMaI.m11 + Z1 * MtxAdaptMaI.m21;
    const Z2 =
        X1 * MtxAdaptMaI.m02 + Y1 * MtxAdaptMaI.m12 + Z1 * MtxAdaptMaI.m22;

    const r = compand(
        X2 * MtxXYZ2RGB.m00 + Y2 * MtxXYZ2RGB.m10 + Z2 * MtxXYZ2RGB.m20
    );
    const g = compand(
        X2 * MtxXYZ2RGB.m01 + Y2 * MtxXYZ2RGB.m11 + Z2 * MtxXYZ2RGB.m21
    );
    const b = compand(
        X2 * MtxXYZ2RGB.m02 + Y2 * MtxXYZ2RGB.m12 + Z2 * MtxXYZ2RGB.m22
    );

    return [r * 255, g * 255, b * 255];
};

export default lab2rgb;
export { xyz2rgb };