Message-ID: 3A13BED6.8141BD22@planetinternet.be
To: "Myers, Randall" <rmyers@dgexchange.dg.com>, TIFF Mailing List <tiff@olympiakos.com>
Subject: Re: Has something changed with error detection in group4 data?
From: Joris Van Damme <as.van.damme.joris@planetinternet.be>
Date: Thu, 16 Nov 2000 12:02:46 +0100
Organization: AWare Systems
References: <FD7E8A8A5060D1119AEF0000F806A97F096E074B@imps0024>
Sender: owner-tiff@olympiakos.com


"Myers, Randall" wrote:
> the worst
> case (no errors detected when they clearly exist)

Is this the worst case? In my use of LibTiff, I'm confronted with a very
related though opposite problem. It seems the library can go on and
produce a reasonable image sometimes even after an error has been
omitted. This, from my point of view, is a bug. An error should envoke
the LibTiff encapsulator to give up on the image (mine does). If not,
chances are that even bigger problems (in the order of crashes and
non-predictable behaviour) might occur. Therefore, in my opinion, if the
library can go on decoding the image, a warning should be emitted
instead of an error. That is the key difference between a warning and an
error, actually, in my humble opinion.

And no, the result code from the LibTiff functions are not a reliable
way to see if the library can go on or not. I've found them to be
totally unreliable. If I listen to these, many images are returned that
are just plain empty and useless, and clearly should have been treated
as fatally unreadable.

Indeed, I've got the impression that this faulty warning/error behaviour
is a big issue espessially in the g3/g4 fax decoders. Perhaps it ought
to be cleaned that up, and rendered predictable, reliable and
systematic.

> In the past I have been able to correlate the behavior (with regard
> to corrupt images) of "tiffinfo -D" and that of the readers which
> our customers use (Microsoft Imaging). 

Indeed, it would be nice if there were a correlation. After all, the
warning/error behaviour should tell the user more about the acutal image
file than about the actual image reader. At least, that's my opinion.



Joris


