2022.12.11 20:18 "Re: [Tiff] libtiff v4.5.0 release candidate available", by Sam James
I had a quick look at it.
Within libitff, the number of directories / directory number is stored in an uint16_t and the number 65535 was treated as a magic number for a "non-existing directory"! Thus, libtiff can only handle 65534 directories.
However, many libtiff functions do not depend on the directory number. Therefore, it is in principle possible to handle TIFF files with more than 65535 IFDs if none of these functions that use the directory number are used. Like the test file gray.movie.u2.tif containing 65567 pages.
Before version 4.5.0, the existing IFD loop check was ineffective. Therefore, no warnings occur for test files with more than 65534 directories.
Since the directory number is contained as a uint16_t in public libtiff interfaces, I see no quick solution at the moment other than to disable the IFD loop check again.
Note that 4.5.0 will change SONAME so it's an opportunity to change that if you want.