Multi-image TIFFs, subfiles and image file directories

[bitsgalore]

https://www.bitsgalore.org/2024/03/11/multi-image-tiffs-subfiles-and-image-file-directories

[bitsgalore]

Just as I thought I had seen it all, @tballison drew my attention to the TIFF attached to this Github issue.

This is obviously a multi-page TIFF, but for some reason ExifTool doesn't report the SubfileType tag for any of the 3 IFDs. On the other hand, JHOVE does report 3 NewSubfileType tags. Interestingly, the ExifTool output shows that each IFD contains a PreviewImage (which apparently isn't implemented as a SubIFD).

Opening the file in Gimp gives a warning that the file is a "Non-conformant TIFF" with "extra channels without 'ExtraSamples' field". The Pinta image editor fails with a "Failed to load RGB data from TIFF file" error, and JHOVE thinks the file is "Well-Formed and valid" TIFF 6.0.

Not entirely sure at this stage whether this is some weird edge case, or perhaps there's even more to multipage TIFFs than I initially thought.