colorjs.io/src/spaces/prophoto.js

Let’s get serious about color

import RGBColorSpace from "../RGBColorSpace.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 => {
			let sign = v < 0 ? -1 : 1;
			let abs = v * sign;

			if (abs < Et2) {
				return v / 16;
			}

			return sign * abs ** 1.8;
		});
	},
	fromBase (RGB) {
		return RGB.map(v => {
			let sign = v < 0 ? -1 : 1;
			let abs = v * sign;

			if (abs >= Et) {
				return sign * abs ** (1 / 1.8);
			}

			return 16 * v;
		});
	},
});