2004.09.17 06:35 "Re: [Tiff] BigTIFF Tag Value Count issue", by Rob van den Tillaart

Hi,

That is indeed the case, so there is an extra option. Allow me to resume and index all three options, then

Option 0: stick with 4 byte tag count members (alignment, tag data <= 4 gig, Frank's choice)
Option 1: make it an 8 byte tag count (no alignment, tag data > 4 gig allowed)
Option 2, courtesy of Bob: make it 8 byte tag count, add 4 padding bytes (alignment, tag data > 4 gig allowed)

There is another option to get 8 byte alignment, so instead of 4 padding bytes they are used for extending the first 2 fields => aligning every field to 32 bit. This might be easier to handle by processors [less complex masking]

Offset - Datatype - Value
--------------------------
0 - ULONG - Tag identifying code
4 - ULONG - Datatype of tag data
8 - Unsigned Long - Number of values
8 - 4 bytes - Tag data or offset

regards,
rob