meta-for BufferedImage also as WidthAndHeight {
  svoid assertSameSize(BufferedImage a, BufferedImage b) {
    int w1 = a.getWidth(), w2 = b.getWidth();
    int h1 = a.getHeight(), h2 = b.getHeight();
    if (w1 != w2 || h1 != h2)
      fail("Different sizes: " + w1 + "*" + h1 + " vs " + w2 + "*" + h2);
  }
}