2004.10.02 01:21 "Re: [Tiff] Re: BigTIFF extension issue", by Joris Van Damme

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 That is merely logical, no user expect up to date behaviour from an outdated version.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
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