public void merge() throws IOException, Exception
    {
        List<String> tifs = new ArrayList<>(fileList.keySet());
        Collections.sort(tifs);

        for (String key : tifs)
        {
            List<File> files = fileList.get(key);

            // Sorter når der et behov for at listen er sorteret, ikke mens der hentes ud
            Collections.sort(files);

            int numTifs = files.size();
            BufferedImage image[] = new BufferedImage[numTifs];
            for (File page : files)
            {
                SeekableStream ss = new FileSeekableStream(page);
                ImageDecoder decoder = ImageCodec.createImageDecoder("tiff", ss, null);
                PlanarImage pi = new NullOpImage(decoder.decodeAsRenderedImage(0), null, null, OpImage.OP_IO_BOUND);
                image[files.indexOf(page)] = pi.getAsBufferedImage();
                ss.close();
            }
            TIFFImageReaderSpi tiffReader = new TIFFImageReaderSpi();
            ImageReader reader = tiffReader.createReaderInstance();
            reader.setInput(pageNumbers);
            TIFFImageWriterSpi tiffWriter = new TIFFImageWriterSpi();
            ImageWriter writer = tiffWriter.createWriterInstance();

            FileImageOutputStream fileImageOutputStream = new FileImageOutputStream(new File(too.getPath() + "\\" + key + ".tif"));
            writer.setOutput(fileImageOutputStream);
            List<BufferedImage> list = new ArrayList<BufferedImage>(image.length);
            for (int i = 1; i < image.length; i++)
            {
                list.add(image[i]);
            }
//            params.setExtraImages(list.iterator());
//            encoder.encode(image[0]);
//            out.close();


            int targetIndex = 0;
            boolean firstPage = true;
            for(int sourceNumber : pageNumbers)
            {
                    IIOMetadata metadata = reader.getImageMetadata(sourceNumber - 1);
                if (firstPage)
                {
                    writer.write(null, new IIOImage(reader.readAsRenderedImage(1, null), null, metadata), null);
                }
                else
                {
                    writer.writeInsert(targetIndex++, new IIOImage(reader.readAsRenderedImage(0 , null), null, metadata), null);
                }

            reader.dispose();
            writer.dispose();
//            return this;
            }


//            TIFFEncodeParam params = new TIFFEncodeParam();
//            params.setCompression(TIFFEncodeParam.COMPRESSION_DEFLATE);
//
//            OutputStream out = new FileOutputStream(too.getPath() + "\\" + key + ".tif");
//            ImageEncoder encoder = ImageCodec.createImageEncoder("tiff", out, params);
//            List<BufferedImage> list = new ArrayList<BufferedImage>(image.length);
//            for (int i = 1; i < image.length; i++)
//            {
//                list.add(image[i]);
//            }
//            params.setExtraImages(list.iterator());
//            encoder.encode(image[0]);
//            out.close();
        }
        JOptionPane.showMessageDialog(rootPane, "Done!");
    }