static BufferedImage copyImage(BufferedImage bi) {
  if (bi == null) null;
  ColorModel cm = bi.getColorModel();
  boolean isAlphaPremultiplied = cm.isAlphaPremultiplied();
  WritableRaster raster = bi.copyData(bi.getRaster().createCompatibleWritableRaster());
  return new BufferedImage(cm, raster, isAlphaPremultiplied, null);
}