colorjs.io/src/spaces/rec2100-pq.js

Let’s get serious about color

import RGBColorSpace from "../rgbspace.js";
import REC2020Linear from "./rec2020-linear.js";

const Yw = 203;	// absolute luminance of media white, cd/m²
const n = 2610 / (2 ** 14);
const ninv = (2 ** 14) / 2610;
const m = 2523 / (2 ** 5);
const minv = (2 ** 5) / 2523;
const c1 = 3424 / (2 ** 12);
const c2 = 2413 / (2 ** 7);
const c3 = 2392 / (2 ** 7);

export default new RGBColorSpace({
	id: "rec2100pq",
	name: "REC.2100-PQ",
	base: REC2020Linear,
	toBase (RGB) {
		// given PQ encoded component in range [0, 1]
		// return media-white relative linear-light
		return RGB.map(function (val) {
			let x = ((Math.max(((val ** minv) - c1), 0) / (c2 - (c3 * (val ** minv)))) ** ninv);
			return (x * 10000 / Yw); 	// luminance relative to diffuse white, [0, 70 or so].
		});
	},
	fromBase (RGB) {
		// given media-white relative linear-light
		// returnPQ encoded component in range [0, 1]
		return RGB.map(function (val) {
			let x = Math.max(val * Yw / 10000, 0); 	// absolute luminance of peak white is 10,000 cd/m².
			let num = (c1 + (c2 * (x ** n)));
			let denom = (1 + (c3 * (x ** n)));

			return ((num / denom)  ** m);
		});
	},
	formats: {
		color: {
			id: "rec2100-pq"
		},
	},
});