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Subject: Re: [Tiff] Re: BigTIFF extension issue
Date: Sat, 2 Oct 2004 03:21:16 +0200
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> And we can't go back and update Photoshop 4.0 (still in use!) to
> support BigTIFF, or to make it give a reasonable  error message -- 
> it's just going to say "this isn't a valid TIFF file".

I assume that Photoshop 1.0 is saying the same about a tiled TIFF. (I may of
course have version numbers and dates incorrect, but I mean to address the
general issue, of course.) Why was this not a problem back then? As far as
Photoshop 4.0 is concerned, BigTIFF is indeed not a valid TIFF file. It is not
uncommon for applications to not be able to foresee future incompatible versions
of file formats, users do know that, and expect Photoshop 4.0 to eg not know
what a DNG file extension means. That is merely logical, no user expect up to
date behaviour from an outdated version.

Incidently, Photoshop 7.0 is unable to read my YCbCr subsampled images. There's
plenty of other TIFFs it can't read. And that's pretty normal, anyone used to
TIFF knows that even the best of apps usually supports the reading of a limited
subset of TIFF.

>From a practical point of view: when there start being more BigTIFF around then
YCbCr subsampled images, chances are Photoshop 7.0 will not be in use anymore.

I'd like to bring some focus to the most general question: is this a new file
format, or a new version of an existing format? It wouldn't hurt to draw the
logical conclusion about the file extension and such, after answering that
question - that is, I think, the way it's always been done before. Right? Nobody
even suggested changing name to 'Tiled TIFF' and extension to '.ttf', I'm
reasonably sure.

>From this point of view, current applications refusing the new BigTIFF, has
nothing to do with the current applications, but everything with the fact that
we chose to not design BigTIFF to be backwards compatible with classic TIFF
readers, for which we had very good reasons. One backwards compatible option was
explored (http://www.asmail.be/msg0055356585.html), but it was quite rightly
quickly judged to be way too much hassle and way to ugly.

I feel the primary issue is: Is BigTIFF a new version? Or is it a new file
format? Let's decide, and be consistent, is what I propose. Do you plan to write
a new spec, or write a new version of the spec, that should give some indication
as to this question, and do we plan to design new codecs, or write new versions
of the existing ones? Seems that's all very related. If this is merely a new
version of an existing file format... It is extremely uncommon at the very least
to have version dependent file extensions, is it not?


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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