Jimp 中值滤波，随便写来测试用的，没优化，效率很低

jimp.medianBlur.js

Jimp.prototype.medianBlur = function () {
  const pointsOffset = [-1, 0, 1].flatMap(x => [-1, 0, 1].map(y => [x, y]));
  const newData = Buffer.from(this.bitmap.data);
  this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, function (x, y, idx) {
    if (x === 0 || x === this.bitmap.width - 1 || y === 0 || y === this.bitmap.height - 1) return;
    for (let i = 0; i < 3; i++) {
      const points = pointsOffset.map(([ox, oy]) => this.bitmap.data[this.getPixelIndex(x + ox, y + oy) + i]);
      points.sort();
      const median = points[Math.floor((points.length - 1) / 2)];
      newData[this.getPixelIndex(x, y) + i] = median;
    }
  });
  this.bitmap.data = newData;
  return this;
};