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From: "Joris" <joris.at.lebbeke@skynet.be>
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Subject: Re: [Tiff] EXIF tags
Date: Sat, 13 Nov 2004 15:50:40 +0100
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> Of course, this issue has not significant importance, but it is
> interesting to clarify this anyway.

I agree it is not of primary significant importance. You'll need to add the
concept of 'tag namespace' to LibTiff anyway, to support EXIF IFDs, if that's
what you're doing, and in either case, it does seem to be the right way to
handle it and does not seem to yield any problem.

But I also agree it is interesting enough to try and clarify.

My understanding is that EXIF, as it is today (private IFD oriented) is similar
to Rome in that it wasn't build in a day. Early day attempts at adding some EXIF
information to TIFF files was private tag oriented, rather then private IFD
oriented. That is why to this day some EXIF tags are legit private tags, as well
as private EXIF IFD tags, which explains their numerical range. When the private
EXIF IFD scheme came about, the early day private tags simply got duplicated to
the EXIF IFD private namespace, and the new additional tags in that private
namespace got a code in the same numerical range...

So, in short, this suspicious numerical range is probably explained by history.
Most important to us is that it doesn't invalidate the 'private namespace'
approach.

Joris Van Damme
info@awaresystems.be
http://www.awaresystems.be
Download your free TIFF tag viewer for windows here:
http://www.awaresystems.be/imaging/tiff/astifftagviewer.html

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