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Date: Thu, 16 Sep 2004 15:23:39 -0400
From: Frank Warmerdam <warmerdam@pobox.com>
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To: Joris <joris.at.lebbeke@skynet.be>
Subject: Re: [Tiff] BigTIFF Tag Value Count issue
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Joris,

My suggestion is that the tag size (aka count field) should be only 4 bytes
mostly because I don't want people writing extremely large tag values.  Typical
libraries (such as libtiff) will actually load all the tag values into
memory as part of reading the data.

I agree with the various points and counter-points you raise. They match up
with the sorts of arguments I have with myself with looking at design
decisions like this.  On balance I feel there is no compelling reason to
support tag values larger than 4GB and reasons to believe that including
such large tag values in a file (even a ways into the future) would
amount to a DOS attack on the app that tries to read the file!

I *do* think that we should allow and support individual tiles or strips
larger than 4GB mainly because some folks still like to write their files
as one big strip and I would hesitate to forbid this.  Well, I would *like*
to forbid this but I'm not sure it would be wise. So I do think the
TileByteCount and StripByteCount tags should be 8bit integers.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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