throws TransformerFactoryConfigurationError, TransformerException, IOException {
final byte [][] data = new byte [imageSets.size()][];
Deflater deflater = new Deflater(Deflater.NO_COMPRESSION);
for (int i=0; i<imageSets.size(); i++) {
final ImageSet imageSet = imageSets.get(i);
deflater.reset();
byte [] compressed = imageSet.compress(ids, deflater);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
InputStream is = new InflaterInputStream(new ByteArrayInputStream(compressed));
byte [] buffer = new byte[16384];
while (true) {