Rec. 2100 HLG

import { registerColorSpace } from "saturon/utils";
import { MATRICES } from "saturon/math";

/**
 * @see {@link https://www.w3.org/TR/css-color-hdr-1/|CSS Color HDR Module Level 1}
 */
registerColorSpace("rec2100-hlg", {
    components: ["r", "g", "b"],
    bridge: "xyz-d65",
    toLinear: (c: number) => {
        const a = 0.17883277;
        const b = 1 - 4 * a;
        const c1 = 0.5 - a * Math.log(4 * a);
        if (c <= 0.5) return c ** 2 / 3;
        return (Math.exp((c - c1) / a) + b) / 12;
    },
    fromLinear: (E: number) => {
        const a = 0.17883277;
        const b = 1 - 4 * a;
        const c1 = 0.5 - a * Math.log(4 * a);
        const sign = E < 0 ? -1 : 1;
        const absE = Math.abs(E);
        if (absE <= 1 / 12) return sign * Math.sqrt(3 * absE);
        return sign * (a * Math.log(12 * absE - b) + c1);
    },
    toBridgeMatrix: MATRICES.REC2020_to_XYZD65,
    fromBridgeMatrix: MATRICES.XYZD65_to_REC2020,
});