2004.09.15 14:32 "[Tiff] reading private subdirs", by Chris Losinger

2004.09.16 15:06 "Re: [Tiff] reading private subdirs", by Chris Losinger

Would you like it better if libtiff itself supported retrieving/storing the EXIF profile so no heavy lifting is required? Since libtiff is currently being enhanced, this is a likely possibility.

yes, i would like that a lot. :)

ideally, for my purposes, i'd be able to tell LibTiff to fetch the EXIF subdir info (and any/all related IFDs). then i'd be able to enumerate the fields it found. and finally, i'd be able to read the data in all of them into my own data structures, to avoid having to re-open (or keep open) the TIFF file. that is roughly what i'm doing now.

and if you add EXIF writing capability, note that re-writing or editing EXIF data almost guarantees that you'll destroy whatever MakerNote data may have been associated with the original file (even if you treat MakerNote data as a binary blob and never touch the internals), because some EXIF writers use tag offsets in their MakerNotes that are based on the start of the EXIF data subdir, rather than the start of the MakerNote subdir. so, changing the length of the non-MakerNote data will destroy all those offsets.

Otherwise, there is improved documentation available at http://www.remotesensing.org/libtiff/addingtags.html now.

i looked at that but didn't see anything about telling LibTiff to read private subdirs. are they automatically read in 3.6.1?

Chris Losinger
Smaller Animals Software, Inc.