File Formats Blog

There is an interesting discussion on the TIFF developer mailing list about buggy tags. Part of the discussion on the IPTC tag, a private tag for IPTC (International Press Telecommunications Council) format metadata, is on the list archive, though the archive usually lags a few days behind. From the opening message:

For starters, the IPTC specification clearly shows how the data is organised in meaningful units of variable bitlength. The *single* correct way to encode that, is using a tag of datatype undefined, and passing the bytecount as tag count (i.e. length of datatype undefined is actually defined, it's the same length as byte).
 
However, some bozo somewhere in the early days of IPTC in TIFF decided to write the stuff as long datatype, with a count such that the tag data length is the length of the IPTC block padded with up to 3 zero bytes.

Adobe itself seems to be one of the violators. Good reading if you're implementing a TIFF reader or writer and need to get into the finer points, or just if you want to understand why some of us aren't convinced TIFF is a standard.

Labels: TIFF

# posted by Gary McGath @ 9:07 AM