colorjs.io/src/spaces/prophoto.js

Let’s get serious about color

import RGBColorSpace from "../rgbspace.js";
import ProPhotoLinear from "./prophoto-linear.js";

const Et = 1 / 512;
const Et2 = 16 / 512;

export default new RGBColorSpace({
	id: "prophoto",
	cssId: "prophoto-rgb",
	name: "ProPhoto",
	base: ProPhotoLinear,
	toBase (RGB) {
		// Transfer curve is gamma 1.8 with a small linear portion
		return RGB.map(v => v < Et2 ? v / 16 : v ** 1.8);
	},
	fromBase (RGB) {
		return RGB.map(v => v >= Et ? v ** (1 / 1.8) : 16 * v);
	},
});