Color space conversions, RGB, XYZ, CIE Lab

color.js

export class RGB {
 constructor(r, g, b, a) {
   this.r = r;
   this.g = g;
   this.b = b;
   this.a = a;
 }
}

function pivotRgb(n) {
   return (n > 0.04045 ? Math.pow((n + 0.055) / 1.055, 2.4) : n / 12.92) * 100.0;
}

export function RGBtoXYZ(color) {
 let r = pivotRgb(color.r / 255.0);
 let g = pivotRgb(color.g / 255.0);
 let b = pivotRgb(color.b / 255.0);

 // Observer. = 2°, Illuminant = D65
 let x = r * 0.4124 + g * 0.3576 + b * 0.1805;
 let y = r * 0.2126 + g * 0.7152 + b * 0.0722;
 let z = r * 0.0193 + g * 0.1192 + b * 0.9505;
 return new XYZ(x, y, z);
}

export class XYZ {
 constructor(x, y, z) {
   this.x = x;
   this.y = y;
   this.z = z;
 }
}

const EPS = 0.008856; // Intent is 216/24389
const KAPPA = 903.3; // Intent is 24389/27

function cubicRoot(n) {
 return Math.pow(n, 1.0 / 3.0);
}

function pivotXyz(n) {
 return n > EPS ? cubicRoot(n) : (KAPPA * n + 16) / 116;
}

const whiteXYZ = new XYZ(
 95.047,
 100.000,
 108.883
);

export function XYZtoCIELAB(color) {
 let x = pivotXyz(color.x / whiteXYZ.x);
 let y = pivotXyz(color.y / whiteXYZ.y);
 let z = pivotXyz(color.z / whiteXYZ.z);

 let L = Math.max(0, 116 * y - 16);
 let a = 500 * (x - y);
 let b = 200 * (y - z);

 return new Lab(L, a, b);
}

export function RGBtoCIELAB(color) {
 return XYZtoCIELAB(RGBtoXYZ(color));
}

export class Lab {
 constructor(L, a, b) {
   this.L = L;
   this.a = a;
   this.b = b;
 }

 // deltaE
 delta(color) {
   let dL = this.L - color.L;

   let C1 = Math.sqrt(this.a * this.a + this.b * this.b);
   let C2 = Math.sqrt(color.a * color.a + color.b * color.b);

   let dC = C1 - C2;

   let da = this.a - color.a;
   let db = this.b - color.b;

   let dH = Math.sqrt(da * da + db * db - dC * dC);

   const kL = 1;
   const K1 = 0.045;
   const K2 = 0.015;

   const kC = 1;
   const kH = 1;

   let SL = 1;
   let SC = 1 + K1 * C1;
   let SH = 1 + K2 * C1;

   return Math.sqrt(
     Math.pow(dL/(kL*SL), 2) +
     Math.pow(dC/(kC*SC), 2) +
     Math.pow(dH/(kH*SH), 2)
   );
 }
}