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March 2005
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2005.03.17 18:57 "Re: libtiff and EXIF", by <ron@debian.org>
On Thu, Mar 17, 2005 at 06:21:32PM +0100, Joris wrote: > > > - Adding a single field to current field info constants. This field would be 0 > > > for most tags. For ExifIFD tag, it would be non-zero, indicating that the tag > > > has IFD pointing intent, and also indicating the index into private, seperate > > > field info name-spaces. > > > > I'm not sure I follow on this, the ExifIFD tag is registered (or at > > least published in a widely accepted standard, which is good enough > > for me if not adobe ;-) so we already know this is its intent. > > Yes, we do. I'm not talking about us though, but about LibTiff, about the const > TIFFFieldInfo array defined in tif_dirinfo.c. LibTiff currently has no > indication that a tag of datatype long is intended to point to an IFD. Ok, I see what you are getting at. I'm not sure we need to add another field to carry this information about though, but yes, its too early to say for sure. > > > - Adding such private, seperate field info name-spaces (I suspect I can save > > > typing by generating the proper C source format from the Tag Directory data). > > > > or what you mean here, though I always like generating things that > > otherwise need to be typed. > > Private IFD tags live in their own, private IFD name-space... > > This is why, if we are to extend LibTiff with true and good private IFD > handling, we'll need to add the notion of seperate tag namespaces.... Yes, with the exception of this additional member, this is the sort of thing I would like to see evolve. An extensible handler for IFD's like we have already for the tags within them. We want a common structure which captures the simple linked list nature of the basic IFD, and then structures which extend it in their own peculiar fashion. But there are still a few things we can do before taking that leap. > I wasn't very clear in my mails to the list. Would you mind posting this reply > that I'm replying to here to the list, so that I can next also post this > clearification? In general, we should really try to keep things on-list. You've > noted there is very little on-list talk on the subject, and part of this problem > is caused by people moving all interesting discussion off-list, leaving the > archive with unanswered questions and unfinished discussions. Actually, speaking as a resident of several busy lists that have reply to list as the default, I'm not sure this is a problem :-) A large part of the reason I actually did subscribe to discuss this is because the list does seem very quiet and high s/n. I'm beginning to suspect this contributes highly to that. I have no objection to anyone reposting salient parts of my off list replies here, in fact I encourage it once there is something of common interest. A lot of intermediate mails can go by that might not fit that bill though, and it doesn't help anyone to clutter the archive with them. The discipline to summarise a useful thread is surely easier to muster than the discipline not to post OT remarks. but now its 5am, so this time I really must go sleep... cheers, Ron