Not sure I care for that solution for single-image TIFFs... seems to be "special-casing" right off the bat...
>From what I can read, maybe the spec needs clarifications such as - in which IFD TIFFtag (52545) goes relative to the data it points to (must be in same IFD in my opinion) - whether data is in an IFD as "raw/image data" or is pure raw data in some other container format at end of file W. Kemp Watson, Managing Director Objective Pathology Services Limited Toronto, Canada On Sun, 15 Mar 2026 at 10:31, Leonard Rosenthol via Tiff < [email protected]> wrote: > Sorry to have taken so long to respond to folks…. > > We’ve been in discussions in the C2PA about what (if any) changes we > should make to our specification to better align with libTIFF and the TIFF > community in general. Here is what we believe is the correct answer - we > would welcome your feedback. > > As previously mentioned by me and also mentioned in our specification, the > C2PA believes that there should only be a single Content Credential in a > given TIFF file - regardless of how many actual images may be present. > This is consistent with all other formats that may contain multiple > assets/images - APNG, JPEG XL, HEIC, etc. > > It is for this reason that we put our data into our own IFD, rather than > associating it with some other (arbitrary) IFD. Based on our reading of > the TIFF v6 spec, and in consultation with the maintainers of TIFF at > Adobe, we consider this a valid position. > > However, in the case where a TIFF contains only a single image (and thus a > single top-level IFD), we are going to change our spec to have the C2PA > Manifest’s IFD be a sub-IFD to that single image - since that makes it > clear that it is associated with that image. That will also make things > more compatible with libTIFF for the most common scenarios. > > Before we finalize this decision for our next revision, we would welcome > your input. > > Thanks, > Leonard > > _______________________________________________ > Tiff mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/tiff >
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