TIFF has been around for a long time. Its latest official specification, TIFF 6.0, dates from 1992. The format hasn’t held still for 23 years, though. Adobe has issued several “technical notes” describing important changes and clarifications. Software developers, by general consensus, have ignored the requirement that value offsets have to be on a word boundary, since it’s a pointless restriction with modern computers. Private tags are allowed, and lots of different sources have defined new tags. Some of them have achieved wide acceptance, such as the TIFFTAG_ICCPROFILE tag (34675), which fills the need to associate ICC color profiles with images. Many applications use the EXIF tag set to specify metadata, but this isn’t part of the “standard” either.
In other words, TIFF today is the sum of a lot of unwritten rules.
It’s generally not too hard to deal with the chaos and produce files that all well-known modern applications can handle. On the other hand, it’s easy to produce a perfectly legal TIFF file that only your own custom application will handle as you intended. People putting files into archives need some confidence in their viability. Assumptions which are popular today might shift over a decade or two. Variations in metadata conventions might cause problems.
A restricted subset of PDF, called PDF/A, specifies rules that help to guarantee the long-term readability of PDF files that follow them. A group of academic archivists has begun work on an initiative to do the same for TIFF, calling it TIFF/A by analogy. It’s supported by the PREFORMA project.
So far it’s still in the stage of gathering support. The site gives September 1, 2015 as the date to kick off discussions and March 1, 2016 as the target for an ISO submission. A white paper by Peter Fornaro and Lukas Rosenthaler at the University of Basel discusses the technical issues. It’s obviously just a first shot at the problem. At one point it states that “it is obvious that the TIFF-extensions [anything which isn’t baseline TIFF] should not be used for long term archival,” but then it admits the ICC profile tag (in fact, says it’s mandatory for color images) and the EXIF tag, and allows the IPTC metadata tag though it doesn’t recommend it.
The white paper doesn’t address the word alignment issue. This is something the TIFF/A consortium needs to take a stand on; either it should repudiate the word alignment requirement, or it should affirm it. If it sticks to strict conformance to the spec, a great many files won’t qualify.
TIFF/A presents a different set of challenges from PDF/A. On the one hand, TIFF is a vastly simpler format than PDF. (Trust me; I’ve written validators for both.) On the other hand, PDF is an ISO standard that hasn’t experienced two decades of entropy. I wish the people involved every success.