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From: "Joris" <joris.at.lebbeke@skynet.be>
To: <tiff@remotesensing.org>
References: <40E0F3A9.8060809@aurigma.com>
Subject: Re: [Tiff] Saving Exif with TiffLib
Date: Tue, 29 Jun 2004 09:29:02 +0200
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> My task is to save Exif-data into tiff-images. According to Exif
> specification I should put Exif-specific data  into subIFDs, that are
> not linked into common directories chain. And, as far as I understand,
> there is no regular mechanism to create such IFDs, because SUBIFD tag,
> specified by TiffLib has its own hardcoded value, while Exif-tags with
> offsets to corresponding Exif-SubIFDs should have other values, that are
> defined by Exif-standart. Should I modify TIffLib (add Exif-tags and
> made some extension of SubIFD-mechanism) to solve my problems, or there
> is any other way?

Alex,

I don't think this is going to be very helpfull, and for that I appologise, but
I just got to say it anyway.

Why is it that the EXIF gets promoted to an IFD? In my humble opinion, any
additional data, like EXIF data, should be a single tag, like all of us mortals
add proprietary data to an IFD. That defines its relationship to the image, ie
the tag is part of the image's IFD. It is by promoting itself to a complete and
independent IFD, that the problem of relationship to the image arises.
Furthermore, it is this promotion that is the cause of your problem here, *and*
is breaking a number of readers that can't make sense of an IFD without
ImageWidth and ImageLength tags (nor should they), *and* is breaking the TIFF
specification in a number of ways, in my humble opinion.

So this comment might not be helpfull, but may nevertheless be worth
considering. Perhaps some people that are more knowledgable than I will respond
to this and perhaps they have a clue what is the sensible thing to do in this
situation.



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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