2011.09.18 14:27 "Re: [Tiff] Write Exif data to Tiff file", by Bob Friesenhahn

I don't really think that libTIFF really wants to start down the metadata "rabbit hole"...

libtiff already supports reading the exif directory,and it already supports modifying tags in an existing exif directory. It just doesn't support *creating* an exif directory. I don't think this is starting down a new path, rather it is completing the functionality.

The tiff.h header file defines about 60 EXIFTAG_* tag names.

This has been a known problem for many many years. Thus far none of the current maintainers have had sufficient motivation to analyze the situation and try to get it to work. It is quite possible that there is a way to make it work with sufficient smarts from user code outside of the library.

It would help if a volunteer would thoroughly analyze all issues and provide a patch to solve this issue.

I do agree with Leonard Rosenthol that libtiff should not be in the business of dealing with EXIF private IFD tags (even though it somewhat does already). What is needed is a way to take a user-provided private IFD blob (perhaps in JPEG-style format with tag offsets from the start of the blob) and add it to the TIFF as a private IFD, while fixing up all tag offsets to so they are offsets from the start of the file (JPEG and TIFF EXIF offsets are different).

There are other libraries which are better suited to dealing with the innards of EXIF profiles.

Bob
--
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/