labh.js

/**
 * Hunter-lab space.
 *
 * @module  color-space/labh
 */

import xyz from './xyz.js';

var labh = {
	name: 'labh',

	//mins/maxes are taken from colormine
	//FIXME: check whether mins/maxes correct
	min: [0, -128, -128],
	max: [100, 128, 128],
	channel: ['lightness', 'a', 'b'],
	alias: ['LABh', 'hunter-lab', 'hlab'],

	//maths are taken from EasyRGB
	xyz: function (lab) {
		var l = lab[0], a = lab[1], b = lab[2];

		var _y = l / 10;
		var _x = a / 17.5 * l / 10;
		var _z = b / 7 * l / 10;

		var y = _y * _y;
		var x = (_x + y) / 1.02;
		var z = -(_z - y) / 0.847;

		return [x, y, z];
	}
};

export default (labh);

//extend xyz
xyz.labh = function (xyz) {
	var x = xyz[0], y = xyz[1], z = xyz[2];
	var _y12 = Math.sqrt(y);
	var l = 10 * _y12;
	var a = y === 0 ? 0 : 17.5 * (((1.02 * x) - y) / _y12);
	var b = y === 0 ? 0 : 7 * ((y - (0.847 * z)) / _y12);

	return [l, a, b];
};