サーモグラフィ風の色変化をシグモイド関数で再現する - Qiita https://qiita.com/masato_ka/items/c178a53c51364703d70b

thermographyRGB.ts

/**
 * サーモグラフィ風の色変化をシグモイド関数で再現する - Qiita
 * https://qiita.com/masato_ka/items/c178a53c51364703d70b
 */

const gain = 10;
const offsetX = 0.2;
const offsetGreen = 0.6;

const sigmoid = (_x: number, _gain = 1, _offsetX = 0) =>
  (Math.tanh(((_x + _offsetX) * _gain) / 2) + 1) / 2;

export const thermographyRGB = (_x: number): [number, number, number] => {
  const x = _x * 2 - 1;
  const r = sigmoid(x, gain, offsetX * -1);
  const b = 1 - sigmoid(x, gain, offsetX);
  const g = sigmoid(x, gain, offsetGreen) - sigmoid(x, gain, offsetGreen * -1);
  return [r, g, b];
};