static BWImage floatArraysToBWImageColumns(int h, L<float[]> l) {
  int w = lengthLevel2_gen(l);
  if (w == 0) null;
  int x = 0;
  BWImage img = new(w, h);
  for (float[] a : l) {
    int ww = l(a);
    for xx to ww: {
      float f = a[xx];
      for y to h:
        img.setPixel(x+xx, y, f);
    }
    x += ww;
  }
  ret img;
}