Working With Private TIFF Tags

private const int MY_SUBIFDTAG = 0xFFFE; 
private const int PRIVATETAG_1 = 0x8001; // use private tags, because LEADTOOLS will reject attempts to write tags below 0x8000 
private const int PRIVATETAG_2 = 0x8002; // use private tags, because LEADTOOLS will reject attempts to write tags below 0x8000 
private const int TAG_COUNT = 2;         // since we will be writing two tags 
private const int TAG_SIZE = 12;         // the number of bytes in one tag 
             
private long GetSubIFDOffset(string fileName) 
{ 
   using (RasterCodecs codecs = new RasterCodecs()) 
   { 
      long[] offsets = null; 
      RasterCollection<RasterTagMetadata> tags = codecs.ReadTagsWithOffsets(fileName, 1, out offsets); 
      uint x = 0; 
      foreach (RasterTagMetadata tag in tags) 
      { 
         if (tag.Id == MY_SUBIFDTAG) 
            return offsets[x]; 
         x++; 
      } 
   } 
             
   return 0; 
} 
             
private void CreateSubIFD(string fileName) 
{ 
   using (RasterCodecs codecs = new RasterCodecs()) 
   { 
      // get the SubIFD offset, if it exists 
      RasterTagMetadata subIFD = null; 
      long subIFDOffset = GetSubIFDOffset(fileName); 
      if (subIFDOffset == 0) 
      { 
         // the SubIFD doesn't exist, write it 
         long ifdSize = 6 + TAG_COUNT * TAG_SIZE; 
         ushort[] ifd = new ushort[ifdSize]; 
         // build the IFD: set the number of tags in the IFD 
         ifd[0] = TAG_COUNT; 
         // and set dummy placeholders for each tag as follows: pIFD[1 + (TAG_SIZE / 2) * tag_index] = tag value 
         ifd[1 + (TAG_SIZE / 2) * 0] = PRIVATETAG_1; 
         ifd[1 + (TAG_SIZE / 2) * 1] = PRIVATETAG_2; 
             
         subIFD = new RasterTagMetadata(); 
         subIFD.Id = MY_SUBIFDTAG; 
         subIFD.DataType = RasterTagMetadataDataType.UInt16; 
         subIFD.FromUInt16(ifd); 
         // write the tag as UNDEFINED 
         subIFD.DataType = RasterTagMetadataDataType.Undefined; 
             
         // write the SubIFD in the file 
         codecs.WriteTag(fileName, 1, subIFD); 
             
         subIFD = null; 
             
         // get the SubIFD offset. It should be > 0 now 
         subIFDOffset = GetSubIFDOffset(fileName); 
         if (subIFDOffset == 0) 
            throw new Exception("failure"); 
      } 
             
      // write the private tags 
      // set private tags 1 and 2 
      RasterTagMetadata privateTag1 = new RasterTagMetadata(); 
      privateTag1.Id = PRIVATETAG_1; 
      privateTag1.DataType = RasterTagMetadataDataType.Int32; 
      privateTag1.FromInt32(new int[] { 5 }); 
             
      RasterTagMetadata privateTag2 = new RasterTagMetadata(); 
      privateTag2.Id = PRIVATETAG_2; 
      privateTag2.DataType = RasterTagMetadataDataType.Ascii; 
      privateTag2.FromAscii("My String"); 
             
      // write the private tags into the SubIFD 
      codecs.Options.Tiff.Save.UseImageFileDirectoryOffset = true; 
      codecs.Options.Tiff.Save.ImageFileDirectoryOffset = subIFDOffset; 
      codecs.WriteTag(fileName, 1, privateTag1); 
      codecs.WriteTag(fileName, 1, privateTag2); 
             
      privateTag1 = null; 
      privateTag2 = null; 
             
      codecs.Options.Tiff.Load.UseImageFileDirectoryOffset = true; 
      codecs.Options.Tiff.Load.ImageFileDirectoryOffset = subIFDOffset; 
             
      // read private tag 1 from SubIFD 
      privateTag1 = codecs.ReadTag(fileName, 1, PRIVATETAG_1); 
      if ((privateTag1.ToInt32())[0] != 5) 
         throw new Exception("Failure"); 
             
      // read private tag 2 from SubIFD 
      privateTag2 = codecs.ReadTag(fileName, 1, PRIVATETAG_2); 
      if (privateTag2.ToAscii() != "My String") 
         throw new Exception("Failure"); 
   } 
}