static LuaValue bwImageToLua(final BWImage img) {
  new LuaTable l;
  l.set("w", Lua.value(img.getWidth()));
  l.set("h", Lua.value(img.getHeight()));
  l.set("getBrightness", new TwoArgFunction {
    BWImage theimg = img; // << queryable by reflection
    
    public LuaValue call(LuaValue x, LuaValue y) {
      ret LuaValue.valueOf(img.getPixel(x.toint(), y.toint()));
    }
  });
  ret l;
}