osaucs.js

/**
 * OSA-UCS
 *
 * @module  color-space/osa-ucs
 */

import xyz from './xyz.js';


var osaucs = {
	name: 'osaucs',
	alias: ['OSA-UCS'],
	channel: ['L', 'j', 'g'],
	min: [-10, -6, -10],
	max: [8, 12, 6]
};


/**
 * There’s no analytical solution to this
 */
osaucs.xyz = function (arg) {
	var x, y, z;

	throw 'Unimplemented';
	//http://www.researchgate.net/publication/259253763_Comparison_of_the_performance_of_inverse_transformation_methods_from_OSA-UCS_to_CIEXYZ

	return [x, y, z];
};


/**
 * Transform to xyz osaucs
 *
 * @param {Array<number>} arg Input xyz array
 *
 * @return {Array<number>} Ljg array
 */
xyz.osaucs = function (arg) {
	var X = arg[0], Y = arg[1], Z = arg[2];

	var x = X / (X + Y + Z);
	var y = Y / (X + Y + Z);

	//FIXME: there might be a typo, wiki states 1.8103 as a constant value
	var K = 4.4934 * x * x + 4.3034 * y * y - 4.276 * x * y - 1.3744 * x - 2.56439 * y + 1.8103;
	var Y0 = K * Y;

	var L_ = 5.9 * (Math.pow(Y0, 1 / 3) - 2 / 3 + 0.042 * Math.pow(Math.max(Y0, 30) - 30, 1 / 3));
	var L = (L_ - 14.3993) / Math.sqrt(2);

	var C = L_ / (5.9 * (Math.pow(Y0, 1 / 3) - 2 / 3));

	var R = 0.7790 * X + 0.4194 * Y - 0.1648 * Z;
	var G = -0.4493 * X + 1.3265 * Y + 0.0927 * Z;
	var B = -0.1149 * X + 0.3394 * Y + 0.7170 * Z;

	R = Math.pow(R, 1 / 3) || 0;
	G = Math.pow(G, 1 / 3) || 0;
	B = Math.pow(B, 1 / 3) || 0;

	var a = -13.7 * R + 17.7 * G - 4 * B;
	var b = 1.7 * R + 8 * G - 9.7 * B;

	var g = C * a;
	var j = C * b;

	//polar form
	// var p = Math.sqrt(j*j + g*g);
	// var phi = Math.atan2(j, g);

	return [L, j, g];
};


export default (osaucs);