text: export function invert(pixels, ratio) {
    const d = pixels.data
    ratio = ratio === undefined ? 1 : ratio
    for (var i = 0; i < d.length; i += 4) {
      d[i] = d[i] + ratio * (255 - 2 * d[i])
      d[i + 1] = d[i + 1] + ratio * (255 - 2 * d[i + 1])
      d[i + 2] = d[i + 2] + ratio * (255 - 2 * d[i + 2])
    }
    return pixels
  }
  