@macrostrat/column-components/dist/chroma-js/src/ops/luminance.js

React rendering primitives for stratigraphic columns

import Color from "../Color.js";
import type from "../utils/type.js";
const { pow } = Math;
const EPS = 1e-7;
const MAX_ITER = 20;
Color.prototype.luminance = function(lum, mode = "rgb") {
  if (lum !== void 0 && type(lum) === "number") {
    if (lum === 0) {
      return new Color([0, 0, 0, this._rgb[3]], "rgb");
    }
    if (lum === 1) {
      return new Color([255, 255, 255, this._rgb[3]], "rgb");
    }
    let cur_lum = this.luminance();
    let max_iter = MAX_ITER;
    const test = (low, high) => {
      const mid = low.interpolate(high, 0.5, mode);
      const lm = mid.luminance();
      if (Math.abs(lum - lm) < EPS || !max_iter--) {
        return mid;
      }
      return lm > lum ? test(low, mid) : test(mid, high);
    };
    const rgb = (cur_lum > lum ? test(new Color([0, 0, 0]), this) : test(this, new Color([255, 255, 255]))).rgb();
    return new Color([...rgb, this._rgb[3]]);
  }
  return rgb2luminance(...this._rgb.slice(0, 3));
};
const rgb2luminance = (r, g, b) => {
  r = luminance_x(r);
  g = luminance_x(g);
  b = luminance_x(b);
  return 0.2126 * r + 0.7152 * g + 0.0722 * b;
};
const luminance_x = (x) => {
  x /= 255;
  return x <= 0.03928 ? x / 12.92 : pow((x + 0.055) / 1.055, 2.4);
};
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