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lab.js
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lab.js
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import { toXYZ, fromXYZ } from "./xyz.js";
import { setAlpha } from "./utils.js";
/**
* @typedef {number[]} lab CIELAB with D65 standard illuminant as default.
*
* Components range (D65): 0 <= l <= 1; -0.86183 <= a <= 0.98234; -1.0786 <= b <= 0.94478;
*
* Components range (D50): 0 <= l <= 1; -0.79287 <= a <= 0.9355; -1.12029 <= b <= 0.93388;
* @see {@link https://en.wikipedia.org/wiki/CIELAB_color_space}
*/
/**
* Illuminant D65: x,y,z tristimulus values
* @private
* @see {@link https://en.wikipedia.org/wiki/Illuminant_D65}
*/
export const D65 = [0.3127 / 0.329, 1, (1 - 0.3127 - 0.329) / 0.329];
export const D50 = [0.3457 / 0.3585, 1, (1 - 0.3457 - 0.3585) / 0.3585];
function fromLabValueToXYZValue(val, white) {
const pow = val ** 3;
return (pow > 0.008856 ? pow : (val - 16 / 116) / 7.787037) * white;
}
function fromXYZValueToLabValue(val, white) {
val /= white;
return val > 0.008856 ? Math.cbrt(val) : 7.787037 * val + 16 / 116;
}
/**
* Updates a color based on Lab values and alpha.
* @param {import("./color.js").color} color
* @param {number} l
* @param {number} a
* @param {number} b
* @param {number} α
* @param {Array} illuminant
* @returns {import("./color.js").color}
*/
export function fromLab(color, l, a, b, α, illuminant = D65) {
const y = (l + 0.16) / 1.16;
return fromXYZ(
color,
fromLabValueToXYZValue(a / 5 + y, illuminant[0]),
fromLabValueToXYZValue(y, illuminant[1]),
fromLabValueToXYZValue(y - b / 2, illuminant[2]),
α,
);
}
/**
* Returns a Lab representation of a given color.
* @param {import("./color.js").color} color
* @param {Array} out
* @param {Array} illuminant
* @returns {lab}
*/
export function toLab(color, out = [], illuminant = D65) {
const xyz = toXYZ(color);
const x = fromXYZValueToLabValue(xyz[0], illuminant[0]);
const y = fromXYZValueToLabValue(xyz[1], illuminant[1]);
const z = fromXYZValueToLabValue(xyz[2], illuminant[2]);
out[0] = 1.16 * y - 0.16;
out[1] = 5 * (x - y);
out[2] = 2 * (y - z);
return setAlpha(out, color[3]);
}