superset-frontend/plugins/legacy-plugin-chart-map-box/src/utils/luminanceFromRGB.js

export const LUMINANCE_RED_WEIGHT = 0.2126;
export const LUMINANCE_GREEN_WEIGHT = 0.7152;
export const LUMINANCE_BLUE_WEIGHT = 0.0722;

export default function luminanceFromRGB(r, g, b) {
  // Formula: https://en.wikipedia.org/wiki/Relative_luminance
  return LUMINANCE_RED_WEIGHT * r + LUMINANCE_GREEN_WEIGHT * g + LUMINANCE_BLUE_WEIGHT * b;
}