private void writePixels(String chunk, byte[] stream, int x, int y, int width, int height)
      throws FormatException, IOException {
    MetadataRetrieve r = getMetadataRetrieve();
    int sizeC = getSamplesPerPixel();
    String type = r.getPixelsType(series).toString();
    int pixelType = FormatTools.pixelTypeFromString(type);
    boolean signed = FormatTools.isSigned(pixelType);

    if (!isFullPlane(x, y, width, height)) {
      throw new FormatException("APNGWriter does not support writing tiles.");
    }

    ByteArrayOutputStream s = new ByteArrayOutputStream();
    s.write(chunk.getBytes());
    if (chunk.equals("fdAT")) {
      s.write(DataTools.intToBytes(nextSequenceNumber++, false));
    }
    DeflaterOutputStream deflater = new DeflaterOutputStream(s);
    int planeSize = stream.length / sizeC;
    int rowLen = stream.length / height;
    int bytesPerPixel = stream.length / (width * height * sizeC);
    byte[] rowBuf = new byte[rowLen];
    for (int i = 0; i < height; i++) {
      deflater.write(0);
      if (interleaved) {
        if (littleEndian) {
          for (int col = 0; col < width * sizeC; col++) {
            int offset = (i * sizeC * width + col) * bytesPerPixel;
            int pixel = DataTools.bytesToInt(stream, offset, bytesPerPixel, littleEndian);
            DataTools.unpackBytes(pixel, rowBuf, col * bytesPerPixel, bytesPerPixel, false);
          }
        } else System.arraycopy(stream, i * rowLen, rowBuf, 0, rowLen);
      } else {
        int max = (int) Math.pow(2, bytesPerPixel * 8 - 1);
        for (int col = 0; col < width; col++) {
          for (int c = 0; c < sizeC; c++) {
            int offset = c * planeSize + (i * width + col) * bytesPerPixel;
            int pixel = DataTools.bytesToInt(stream, offset, bytesPerPixel, littleEndian);
            if (signed) {
              if (pixel < max) pixel += max;
              else pixel -= max;
            }
            int output = (col * sizeC + c) * bytesPerPixel;
            DataTools.unpackBytes(pixel, rowBuf, output, bytesPerPixel, false);
          }
        }
      }
      deflater.write(rowBuf);
    }
    deflater.finish();
    byte[] b = s.toByteArray();

    // write chunk length
    out.writeInt(b.length - 4);
    out.write(b);

    // write checksum
    out.writeInt(crc(b));
  }