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June 1999

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1999.06.03 19:48 "Large File Support", by Bruce Forsberg
1999.06.04 03:45 "Re: Large File Support", by Frank Warmerdam
1999.06.04 07:32 "Re: Large File Support", by Rob Tillaart
1999.06.07 07:05 "Re: Large File Support", by Rainer Wiesenfarth
1999.06.08 21:14 "Re: Large File Support", by Peter Smith
1999.06.08 21:58 "Re: Large File Support", by Ed Grissom
1999.06.08 22:52 "Re: Large File Support", by Peter Smith
1999.06.09 01:27 "Re: Large File Support", by Martin Bailey
1999.06.09 06:50 "Re: Large File Support", by Owen Pearn
1999.06.09 14:33 "Re: Large File Support", by Martin Bailey
1999.06.09 08:07 "Re: Large File Support", by Rob Tillaart
1999.06.04 18:35 "Re: Large File Support", by Bruce Forsberg
1999.06.07 13:03 "Re: Large File Support", by Frank Warmerdam
1999.06.09 03:05 "Re: Large File Support", by <glen@lumisys.com>
1999.06.09 13:13 "Re: Large File Support", by Ed Grissom
1999.06.09 13:33 "Re: Large File Support", by Frank Warmerdam
1999.06.09 14:08 "Re: Large File Support", by Ed Grissom
1999.06.09 18:50 "Re: Large File Support", by Chris Barker
1999.06.09 18:41 "Large File Support", by Chris Barker
1999.06.10 13:21 "Re: Large File Support", by Chris Hanson
1999.06.10 13:52 "Re: Large File Support", by Frank Warmerdam
1999.06.10 14:37 "Re: Large File Support", by John Aldridge
1999.06.10 15:10 "Re: Large File Support", by Peter Smith
1999.06.10 16:56 "Re: Large File Support", by Chris Barker
1999.06.14 11:16 "Re: Large File Support", by Martin Bailey
1999.06.14 14:58 "Re: Large File Support", by Tom Lane
1999.06.14 15:30 "Re: Large File Support", by Eric Shapiro
1999.06.14 16:27 "Re: Large File Support", by Chris Barker
1999.06.14 15:51 "Re: Large File Support", by Martin Bailey
1999.06.09 15:52 "Re: Large File Support", by Ed Grissom
1999.06.10 09:48 "Re: Large File Support", by Klaus Bartz
1999.06.10 13:05 "Re: Large File Support", by Chris Hanson
1999.06.11 01:48 "Re: Large File Support", by <glen@lumisys.com>

1999.06.14 11:16 "Re: Large File Support", by Martin Bailey

I've been pondering the idea of large file support, and especially the
ideal of minimising the impact that any changes would have on existing
readers etc. I see backward compatibility as extremely important to ensure
that any changes would be acceptable both to application creators and to
the user community. As others have already said, we really don't need a new
file format right now.

As I see it the minimum change would be:

* Require that all FIDs and indirectly referenced tag values fall within
the first 4 GB of the file. This means that FID pointers in the header and
at the end of each FID, and value pointers can all remain as 4 bytes. In a
very large file it may be more efficient for some readers if the FIDs are
at the start of the file anyway.

* Add a new tag type - LONG64, maybe also a signed version - SLONG64, with
a strong recommendation that they only be used where required.

* Adjust some tag descriptions, e.g. StripOffsets may currently use a SHORT
or LONG value, add LONG64 to the valid types.

Yes, I know this is a somewhat cludgy, but changes to existing formats
where backward compatibility is an important consideration tend to be.

I also realise that this simple suggestion does not necessarily mean that
it would be simple to update applications to work with large TIFF files. If
a tool is not 64-bit ready it will still be hard to amend it.

What do people think?



Regards

Martin Bailey

----------------------------------------------------------
 Digital Print & Publishing                 Harlequin Ltd
 martinb@harlequin.com           http://www.harlequin.com
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 I try to ensure that my views expressed here accord with
 my employers, but I am not a spokesman for Harlequin and
        the buck stops with me for what I say here
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