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Subject: RE: [Tiff] IPTC tag
Date: Fri, 25 Aug 2006 11:30:52 -0700
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From: "Chris Cox" <ccox@adobe.com>
To: "Phil Harvey" <phil@owl.phy.queensu.ca>,
        "Joris" <joris.at.lebbeke@skynet.be>
Cc: <tiff@lists.maptools.org>
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Status:   

Unfortunately, the TIFF readers that have the bug are in widespread use in the newspaper and magazine industries.

I haven't had a lot of luck getting them to fix even major bugs -- so we constantly try to work around them.

And, sadly, TIFF errors are far too common -- most TIFF readers have a long list of exceptions and corrections (Photoshop's has a LONG list).
As always, it pays to be lenient in what you read, and strict in what you write.  But sometimes you have to write it in a way that other people/applications expect rather than the most correct form.

Chris



-----Original Message-----
From: tiff-bounces@lists.maptools.org on behalf of Phil Harvey
Sent: Fri 8/25/2006 10:37 AM
To: Joris
Cc: tiff@lists.maptools.org
Subject: Re: [Tiff] IPTC tag
 
The one thing we should be able to agree on is that regardless of the 
data type, IPTC data should NOT be byte-swapped when written.  If 
writing with the current version of libTIFF, this means that should be 
written as undefined.  I tried this strategy (writing IPTC as 
undefined) with my software and found users who complained of 
incompatibilities, so I changed to writing long as Adobe does.  For me 
it was an easy change, although I agree that it serves to perpetuate a 
historical 'bug' in the way IPTC is written.  I also agree that it 
would be best if this bug could be eventually squashed, but it looks 
like here I am part of the problem, not the solution.

Along the same lines, I also consider it a bug that IFD offsets are 
written as long (value of 4).  They should be written as IFD type 
(value of 13), otherwise unknown IFD's can not be parsed.  If we're 
trying to fix historical bugs, maybe we could fix this as well.  While 
you may never have been stung by this bug, I have repeatedly because of 
the non-standard TIFF-format information that my software has to deal 
with.

- Phil

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