lab.js

import define, {extend} from "./define";
import {Color, rgbConvert, Rgb} from "./color";
import {deg2rad, rad2deg} from "./math";

var Kn = 18,
    Xn = 0.950470, // D65 standard referent
    Yn = 1,
    Zn = 1.088830,
    t0 = 4 / 29,
    t1 = 6 / 29,
    t2 = 3 * t1 * t1,
    t3 = t1 * t1 * t1;

function labConvert(o) {
  if (o instanceof Lab) return new Lab(o.l, o.a, o.b, o.opacity);
  if (o instanceof Hcl) {
    var h = o.h * deg2rad;
    return new Lab(o.l, Math.cos(h) * o.c, Math.sin(h) * o.c, o.opacity);
  }
  if (!(o instanceof Rgb)) o = rgbConvert(o);
  var b = rgb2xyz(o.r),
      a = rgb2xyz(o.g),
      l = rgb2xyz(o.b),
      x = xyz2lab((0.4124564 * b + 0.3575761 * a + 0.1804375 * l) / Xn),
      y = xyz2lab((0.2126729 * b + 0.7151522 * a + 0.0721750 * l) / Yn),
      z = xyz2lab((0.0193339 * b + 0.1191920 * a + 0.9503041 * l) / Zn);
  return new Lab(116 * y - 16, 500 * (x - y), 200 * (y - z), o.opacity);
}

export default function lab(l, a, b, opacity) {
  return arguments.length === 1 ? labConvert(l) : new Lab(l, a, b, opacity == null ? 1 : opacity);
}

export function Lab(l, a, b, opacity) {
  this.l = +l;
  this.a = +a;
  this.b = +b;
  this.opacity = +opacity;
}

define(Lab, lab, extend(Color, {
  brighter: function(k) {
    return new Lab(this.l + Kn * (k == null ? 1 : k), this.a, this.b, this.opacity);
  },
  darker: function(k) {
    return new Lab(this.l - Kn * (k == null ? 1 : k), this.a, this.b, this.opacity);
  },
  rgb: function() {
    var y = (this.l + 16) / 116,
        x = isNaN(this.a) ? y : y + this.a / 500,
        z = isNaN(this.b) ? y : y - this.b / 200;
    y = Yn * lab2xyz(y);
    x = Xn * lab2xyz(x);
    z = Zn * lab2xyz(z);
    return new Rgb(
      xyz2rgb( 3.2404542 * x - 1.5371385 * y - 0.4985314 * z), // D65 -> sRGB
      xyz2rgb(-0.9692660 * x + 1.8760108 * y + 0.0415560 * z),
      xyz2rgb( 0.0556434 * x - 0.2040259 * y + 1.0572252 * z),
      this.opacity
    );
  }
}));

function xyz2lab(t) {
  return t > t3 ? Math.pow(t, 1 / 3) : t / t2 + t0;
}

function lab2xyz(t) {
  return t > t1 ? t * t * t : t2 * (t - t0);
}

function xyz2rgb(x) {
  return 255 * (x <= 0.0031308 ? 12.92 * x : 1.055 * Math.pow(x, 1 / 2.4) - 0.055);
}

function rgb2xyz(x) {
  return (x /= 255) <= 0.04045 ? x / 12.92 : Math.pow((x + 0.055) / 1.055, 2.4);
}

function hclConvert(o) {
  if (o instanceof Hcl) return new Hcl(o.h, o.c, o.l, o.opacity);
  if (!(o instanceof Lab)) o = labConvert(o);
  var h = Math.atan2(o.b, o.a) * rad2deg;
  return new Hcl(h < 0 ? h + 360 : h, Math.sqrt(o.a * o.a + o.b * o.b), o.l, o.opacity);
}

export function hcl(h, c, l, opacity) {
  return arguments.length === 1 ? hclConvert(h) : new Hcl(h, c, l, opacity == null ? 1 : opacity);
}

export function Hcl(h, c, l, opacity) {
  this.h = +h;
  this.c = +c;
  this.l = +l;
  this.opacity = +opacity;
}

define(Hcl, hcl, extend(Color, {
  brighter: function(k) {
    return new Hcl(this.h, this.c, this.l + Kn * (k == null ? 1 : k), this.opacity);
  },
  darker: function(k) {
    return new Hcl(this.h, this.c, this.l - Kn * (k == null ? 1 : k), this.opacity);
  },
  rgb: function() {
    return labConvert(this).rgb();
  }
}));