static RGBImage rgbClipLineRange(int y1, int y2, RGBImage r) {
  if (r == null) null;
  Rect clip = rect(0, y1, r.image.getWidth(), y2-y1);
  ret clipRGBImage(r.image, clip);
}

static RGBImage rgbClipLineRange(RGBImage r, int y1, int y2) {
  ret rgbClipLineRange(y1, y2, r);
}