static L<RGBImage> rgbImageVerticalSlices(double sliceHeight, RGBImage img) {
  new L<RGBImage> out;
  int w = img.getWidth(), h = img.getHeight();
  for (double y = 0; iround(y) < h; y += sliceHeight) {
    int actualY = iround(y), nextY = min(h, iround(y+sliceHeight));
    if (nextY > actualY)
      out.add(rgbClip(img, rectFromPoints(0, actualY, w, nextY)));
  }
  ret out;
}