chroma-js/src/io/lab/rgb2lab.js

JavaScript library for color conversions

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

const rgb2lab = (...args) => {
    const [r, g, b, ...rest] = unpack(args, 'rgb');
    const [x, y, z] = rgb2xyz(r, g, b);
    const [L, a, b_] = xyz2lab(x, y, z);
    return [L, a, b_, ...(rest.length > 0 && rest[0] < 1 ? [rest[0]] : [])];
};

function xyz2lab(x, y, z) {
    const { Xn, Yn, Zn, kE, kK } = LAB_CONSTANTS;
    const xr = x / Xn;
    const yr = y / Yn;
    const zr = z / Zn;

    const fx = xr > kE ? Math.pow(xr, 1.0 / 3.0) : (kK * xr + 16.0) / 116.0;
    const fy = yr > kE ? Math.pow(yr, 1.0 / 3.0) : (kK * yr + 16.0) / 116.0;
    const fz = zr > kE ? Math.pow(zr, 1.0 / 3.0) : (kK * zr + 16.0) / 116.0;

    return [116.0 * fy - 16.0, 500.0 * (fx - fy), 200.0 * (fy - fz)];
}

function gammaAdjustSRGB(companded) {
    const sign = Math.sign(companded);
    companded = Math.abs(companded);
    const linear =
        companded <= 0.04045
            ? companded / 12.92
            : Math.pow((companded + 0.055) / 1.055, 2.4);
    return linear * sign;
}

const rgb2xyz = (r, g, b) => {
    // normalize and gamma adjust
    r = gammaAdjustSRGB(r / 255);
    g = gammaAdjustSRGB(g / 255);
    b = gammaAdjustSRGB(b / 255);

    const { MtxRGB2XYZ, MtxAdaptMa, MtxAdaptMaI, Xn, Yn, Zn, As, Bs, Cs } =
        LAB_CONSTANTS;

    let x = r * MtxRGB2XYZ.m00 + g * MtxRGB2XYZ.m10 + b * MtxRGB2XYZ.m20;
    let y = r * MtxRGB2XYZ.m01 + g * MtxRGB2XYZ.m11 + b * MtxRGB2XYZ.m21;
    let z = r * MtxRGB2XYZ.m02 + g * MtxRGB2XYZ.m12 + b * MtxRGB2XYZ.m22;

    const Ad = Xn * MtxAdaptMa.m00 + Yn * MtxAdaptMa.m10 + Zn * MtxAdaptMa.m20;
    const Bd = Xn * MtxAdaptMa.m01 + Yn * MtxAdaptMa.m11 + Zn * MtxAdaptMa.m21;
    const Cd = Xn * MtxAdaptMa.m02 + Yn * MtxAdaptMa.m12 + Zn * MtxAdaptMa.m22;

    let X = x * MtxAdaptMa.m00 + y * MtxAdaptMa.m10 + z * MtxAdaptMa.m20;
    let Y = x * MtxAdaptMa.m01 + y * MtxAdaptMa.m11 + z * MtxAdaptMa.m21;
    let Z = x * MtxAdaptMa.m02 + y * MtxAdaptMa.m12 + z * MtxAdaptMa.m22;

    X *= Ad / As;
    Y *= Bd / Bs;
    Z *= Cd / Cs;

    x = X * MtxAdaptMaI.m00 + Y * MtxAdaptMaI.m10 + Z * MtxAdaptMaI.m20;
    y = X * MtxAdaptMaI.m01 + Y * MtxAdaptMaI.m11 + Z * MtxAdaptMaI.m21;
    z = X * MtxAdaptMaI.m02 + Y * MtxAdaptMaI.m12 + Z * MtxAdaptMaI.m22;

    return [x, y, z];
};

export default rgb2lab;
export { rgb2xyz };