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From: "Kemp Watson" <kemp@extelligence.net>
To: "Joris" <joris.at.lebbeke@skynet.be>,
        "Stephen Carlsen" <sc42business@mac.com>
Subject: RE: [Tiff] BigTIFF extension
Date: Thu, 5 Jul 2007 00:19:16 -0400
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Status:   

I fully agree with Joris. Fact is, TIFF readers rarely support all of TIFF possibilities - it's already a complex
format, and this is simply yet another extension. The version number is a convenience, and compared with the vast array
of sporadically supported features in v.42, it has next to no meaning. Not saying I agree with that, but it's the way it
is - _any_ TIFF reader has to iterate over quite a number of tags to determine whether it's capable of handling a
particular file - I fail to see how this is in _any_ way different.

In short, choosing ".tif" in a dialog says absolutely nothing about the readability of a TIFF file.

Kemp Watson


-----Original Message-----
From: Joris [mailto:joris.at.lebbeke@skynet.be]
Sent: July 4, 2007 10:42 PM
To: kemp@extelligence.net; Stephen Carlsen
Cc: tiff@lists.maptools.org
Subject: Re: [Tiff] BigTIFF extension


Stephen,

Stephen Carlsen wrote:
> "Because, for the first time in the 21 year history of TIFF, the
> structure itself has changed, and, accordingly, the 'version number'
> has changed from 42 to 43. (The 'version number' has, of course, been
> 42 since the very beginning of TIFF.) This breaks all existing TIFF
> readers."

The exact same thing applies to the coming of tiles in TIFF. It wasn't the
structure itself that had changed at that time, but it was some of the
extremely vital tags, which resulted in the same. It broke all existing TIFF
readers. Your reasoning would have applied back then, too, and we'd be
forced to use 'tf3' as an extension right now because 'tf2' would have been
taken for tiled TIFF. No, actually, we would be forced to use 'tf3' for
striped BigTIFF and 'tf4' for tiled BigTIFF, probably.

Put things to this extreme, and you can end up encoding all information in
the extension. That's not a good thing to do. Put the exact information
where it belongs, not more and not less, and don't code anything twice. The
extension is for marking the file format, and that's TIFF in both
ClassicTIFF and BigTIFF version. The version number, in turn, marks the
version. That's just good, and truthfull information encoding management.


Best regards,

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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