@onesy/utils/esm/quantize.js

Utils

const colorRange = value => {
  const min = new Array(3).fill(Number.MAX_VALUE);
  const max = new Array(3).fill(Number.MIN_VALUE);
  value.forEach(item => {
    item.forEach((value_, index) => {
      min[index] = Math.min(min[index], value_);
      max[index] = Math.max(max[index], value_);
    });
  });
  const ranges = min.map((item, index) => max[index] - item);
  const maxRange = Math.max(...ranges);
  if (maxRange === ranges[0]) return 0;else if (maxRange === ranges[1]) return 1;
  return 2;
};

const quantizeMethod = function (value) {
  let depth = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 0;
  const MAX_DEPTH = 7;
  if (!value.length) return [];

  if (MAX_DEPTH === depth) {
    const color = value.reduce((result, item) => {
      item.forEach((value_, index) => result[index] += value_);
      return result;
    }, [0, 0, 0]);
    return [color.map(item => Math.round(item / value.length))];
  }

  const sortIndex = colorRange(value);
  value.sort((a, b) => a[sortIndex] - b[sortIndex]);
  const mid = value.length / 2; // Reverse so primary is a first value

  return [...quantizeMethod(value.slice(0, mid), depth + 1), ...quantizeMethod(value.slice(mid + 1), depth + 1)].reverse();
};

const quantize = function (value) {
  let amount = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 4;
  const depth = 7 - Math.ceil(Math.log2(amount));
  return quantizeMethod(value, depth).slice(0, amount);
};

export default quantize;