// Initialize a memory mapped byte buffer for accessing the FITS image data, if
// possible
private void _initByteBuffer() throws IOException {
ArrayDataInput arrayDataInput = _fits.getStream();
if (arrayDataInput instanceof BufferedFile) {
//System.out.println("XXX FITSImage: using BufferedFile");
long headerSize = _header.getSize();
long offset = _hdu.getFileOffset() + headerSize;
long size = _hdu.getSize() - headerSize;