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2007.07.05 20:39 "Re: Tiff Digest, Vol 38, Issue 16", by Kemp Watson
Craig: Unfortunately, this is not quite true :( First, a BigTIFF file is distinct from a BigTIFF tool. Gary's comment that an existing TIFF reader can't read a BigTIFF file is correct. That's not the same as being able to read a ClassicTIFF file generated by a BigTIFF tool. Also, for borderline file sizes, the BigTIFF writer cannot in advance practically determine the resultant file size after compression, especially lossy, and is thus not really able to make a really exact automatic decision on file format prior to beginning compression; i.e. the writing application will _NOT_ normally know all of the parameters before-hand to make this decision. My opinion here is that part of what Aperio did does make some sense - have a flag or function that allows the compressor to specify perhaps one of these options: - compress with ClassicTIFF, and accept possibility of failure if file> 4GB - compress with BigTIFF - let the tool decide, try, and rewrite if the tool guessed wrong initially (risk of time loss, but best compatibility result). Probably biased toward trying ClassicTIFF first in the borderline cases. I would hazard a guess that the default should be the third option. Kemp Watson Date: Thu, 5 Jul 2007 14:51:20 -0400 From: Craig Bruce <csbruce@cubewerx.com> Subject: Re: [Tiff] Re: BigTIFF To: tiff@lists.maptools.org Message-ID: <200707051851.l65IpKMf005318@tux.cubewerx.com> Content-Type: text/plain; charset="iso-8859-1" Gary McGath <gary@hulmail.harvard.edu> wrote: > The possibility of modifying and rebuilding software to make it > compatible is not the same as compatibility in existing software. If > you run any existing TIFF reader on any BigTIFF file, the reader will > be unable to interpret it. I believe the BigTIFF spec says something to the effect that if the writing application determines that it will not be generating a >4GB file that it should write ClassicTIFF instead. Therefore, "BigTIFF" is 100% compatible with all existing software up to 4GB. The writing application will normally know all of the parameters before-hand to make this decision. BigTIFF is also 100% compatible with all existing software for ClassicTIFF images above 4GB. (Since there is no such thing.) So there you have it -- 100% compatibility No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.476 / Virus Database: 269.10.0/886 - Release Date: 04-Jul-2007 1:40 PM