docs: function(pixels, data) {
      const pixel = pixels[0];
      const value = vgi(pixel);
      summarize(value, data.counts);
      if (value >= data.threshold) {
        pixel[0] = 0;
        pixel[1] = 255;
        pixel[2] = 0;
        pixel[3] = 128;
      } else {
        pixel[3] = 0;
      }
      return pixel;
    }