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From: "Joris" <joris.at.lebbeke@skynet.be>
To: <tiff@lists.maptools.org>, "Oliver Geisen" <oliver.geisen@kreisbote.de>
References: <F38EDE7C-E456-4DD0-8227-7F60F83155A4@kreisbote.de>
Subject: Re: [Tiff] FILLORDER = 25920 ??
Date: Tue, 10 Jul 2007 17:24:06 +0200
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Status: RO

Oliver,

Oliver Geisen wrote:
> what if a regular bilevel TIFF (G4-Compressed) tells me to have an
> FILLORDER of 25920 ?!
> I thought this could only be 1 or 2.

Any and all corruption and bad values occur, given sufficient time, in the 
files 'out there'. I don't know of any standard or de facto usage of 
FILLORDER other then 1 or 2, so in the absence of more information, the best 
we can do is classify this as corruption or bad value.

The standard behaviour when dealing with total undefined values for basic 
tags required in the decoding process, is to revert to their default value. 
It may not make sense, but it's the best chance you have of possibly 
rendering a seemingly correctly decoded image. You should also have a 
'warnings' system, and emit a warning for this situation, so that in the 
event your user sees a decoding and rendering clearly different from the 
intention, the user is able to trace the likely origin of the problem.

A more careful approach is to fail with proper error message. This is more 
careful, in that there's no chance of emitting an image different from 
writer's intention. But there's also no chance of robustly recovering and 
making some sense, so it cuts both ways.


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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