static Map<BWImage, S> loadGlyphSheet(S sheetID) {
  L<BWImage> images = unclusterImages(loadBWImage(sheetID));
  if (images == null) fail("Unclustering failed!?");
  images = map(func(BWImage i) { removeGrayBorder(i) }, images);
  Map<BWImage, S> map = litorderedmap();
  for (BWImage img : images) {
    continue if img == null;
    Pair<BWImage, S> p = unsubtitle(img);
    if (p == null)
      print("Unsubtitle failed");
    else
      map.put(p.a, p.b);
  }
  ret map;
}