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From: "Joris" <joris.at.lebbeke@skynet.be>
To: "Gary McGath" <gary@rockhop.harvard.edu>, <tiff@lists.maptools.org>
References: <43909A98.8030303@hulmail.harvard.edu>
Subject: Re: [Tiff] Odd offsets in IFD entries
Date: Sun, 4 Dec 2005 00:53:15 +0100
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Status:   

Gary McGath wrote:
> In TIFF, are all offsets specified by an IFD entry required to be on
> an even byte boundary?

Yes, absolutely.

> But we've
> encountered large numbers of files that violate this requirement and
> still work with existing software.

In TIFF, strict validation with binary result is mostly useless. This
word alignment of data blocks is just one of the rules that are often
violated, but don't really matter much to most readers. A full
diagnostic is more feasable, less arbitrarilly, and more usefull. It
allows you to state the exact violation(s), the severity and impact on
mainstream readers, etc.

A TIFF with floating point image date, or with a 3bits per pixel
palette, may be perfectly legit, but nevertheless not supported by most
mainstream readers. A full diagnostic output of a validator allows you
to include comments on portability in these cases.


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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