c0lor/space/lab.js

Color space conversions

var Lab, N, O, e, e3, f, fDeriv, fInv, foo, labCsPrototype, pow, xyz;

O = require("ut1l/create/object");

xyz = require("../XYZ");

Lab = require("../Lab");

pow = Math.pow;

N = 4 / 29;

e3 = 216 / 24389;

foo = 841 / 108;

e = 6 / 29;

f = function(w) {
  if (w > e3) {
    return pow(w, 1 / 3);
  } else {
    return foo * w + N;
  }
};

fInv = function(w) {
  if (w > e) {
    return pow(w, 3);
  } else {
    return (w - N) / foo;
  }
};

fDeriv = function(w) {
  if (w > e3) {
    return 1 / (3 * (pow(w, 2 / 3)));
  } else {
    return foo;
  }
};

labCsPrototype = {
  Lab: function(XYZ, T) {
    var l;
    if (T == null) {
      T = Lab();
    }
    l = f(XYZ.Y / this.white.Y);
    T.L = 116 * l - 16;
    T.a = 500 * ((f(XYZ.X / this.white.X)) - l);
    T.b = 200 * (l - (f(XYZ.Z / this.white.Z)));
    return T;
  },
  XYZ: function(Lab, T) {
    var fy;
    if (T == null) {
      T = xyz();
    }
    fy = (Lab.L + 16) / 116;
    T.X = (fInv(fy + Lab.a / 500)) * this.white.X;
    T.Y = (fInv(fy)) * this.white.Y;
    T.Z = (fInv(fy - Lab.b / 200)) * this.white.Z;
    return T;
  },
  LabderivL: function(Y) {
    return 116 * (fDeriv(Y / this.white.Y)) / this.white.Y;
  }
};

module.exports = O((function(white) {
  this.white = white;
}), labCsPrototype);