public synchronized void removeUnsafeToCopyPrivateChunks() {
        List newChunkType = new ArrayList();
        List newChunkData = new ArrayList();

        int len = getNumPrivateChunks();
        for (int i = 0; i < len; i++) {
            String type = getPrivateChunkType(i);
            char lastChar = type.charAt(3);
            if (lastChar >= 'a' && lastChar <= 'z') {
                newChunkType.add(type);
                newChunkData.add(getPrivateChunkData(i));
            }
        }

        chunkType = newChunkType;
        chunkData = newChunkData;
    }
Remove all private chunks associated with this parameter instance
whose 'safe-to-copy' bit is not set.  This may be advisable when
transcoding PNG images.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java