2006-10-25 05:56:59 -04:00
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<title>Proposal to Implement BigTIFF Support in LibTiff</title>
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<h1>Proposal to Implement BigTIFF Support in LibTiff</h1>
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2006-12-24 07:11:05 -05:00
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<p><b>NEWS:</b> We have located all four required sponsors. There are no more
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2007-03-02 13:36:11 -05:00
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open slots. We will issue appropriate press release shortly.</p>
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2006-10-25 05:56:59 -04:00
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<h2>0. Summary</h2>
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<p>BigTIFF logically extends the original TIFF file format (referred to as
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'ClassicTIFF' from this point on), breaking the 4 gigabyte boundary, in theory
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allowing files up to 18,000 petabytes in size. The BigTIFF specification is the
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result of work by a variety of parties on the LibTiff mailing list, including
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the current LibTiff maintainers, Joris Van Damme and Adobe staff. The BigTIFF
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specification has not yet been officially approved by the TIFF specification
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owner (Adobe) but implementation within LibTiff could accelerate that
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process.</p>
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<p>For more information on the BigTIFF file format, we recommend
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<a href="http://www.awaresystems.be/imaging/tiff/bigtiff.html">AWare Systems'
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BigTIFF page.</a></p>
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<p>BigTIFF is expected to be especially useful for people and vendors that are
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confronted with unusually large images, and still seek to use an open, simple,
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and extendable format. This requirement is frequently seen in the geospatial
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field, but also affects large format scanners, medical imaging and other
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fields.</p>
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<h2>1. Sponsoring</h2>
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<p>It is planned that LibTiff 4.0, the BigTIFF upgrade to LibTiff, would start
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March 1, 2007. A preliminary version (LibTiff 4.0alpha1) will be operational by
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June 15, 2007. Testing and final release improvements for LibTiff 4.0 will be
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completed by July 30, 2007.</p>
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<p>The LibTiff BigTIFF upgrade team is seeking USD 24,000 from four sponsors (USD
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6,000 each) to fund the project. Sponsorship payment will be invoiced upon
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delivery of the LibTiff 4.0alpha1 release (on or before June 15) with a 30 day
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payable, giving time for some technical review.</p>
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<p>In addition to the benefits of open interchange of BigTIFF data that comes from
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support in a public and free open source codec, sponsors will be given proper
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public acknowledgment. During development, they will be mentioned in the
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appropriate sections of the LibTiff and AWare Systems site.</p>
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<p>When LibTiff 4.0 with BigTIFF support is released, they will additionally
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receive public acknowledgment in a formal press release, distributed widely to
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news venues in the imaging and geospatial industries.</p>
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<p>A 'migration guide' document or any functional equivalent thereof will be
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included in the standard free distribution, but sponsors will additionally
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receive up to 20 hours of consulting and support on any BigTIFF migration issues
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that they may be facing, and/or any additional related requests they may have.</p>
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<h2>2. Development and Testing</h2>
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<p>The work will primarily be done by Joris Van Damme on behalf of his company
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AWare Systems. Joris was closely involved in the drafting of the BigTIFF file
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format proposal, and has also developed the proprietary AWare Systems TIFF
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codec that already supports BigTIFF. Joris Van Damme has a deep understanding
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of the TIFF format, and has been acting as a LibTiff co-maintainer for over a
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year, contributing the upgraded OJPEG codec as well as several other
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improvements.</p>
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<p>Joris and AWare Systems have agreed to crosstest their proprietary codec and
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LibTiff's support for BigTIFF extensively. Joris will also extend the test image
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library included with LibTiff, with a number of varying BigTIFF test files.
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These files will primarily include test files with issues that relate closely
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to the BigTIFF file format and the difference with ClassicTIFF. For instance,
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in BigTIFF the datatypes TIFF_LONG, TIFF_LONG8, TIFF_IFD and TIFF_IFD8 are all
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valid for tags pointing to additional IFDs, and thus files will be included to
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illustrate and enable testing all of these. Additionally, Joris will build a
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tool to enable creating test files that exceed 4 gigabyte, as these can of
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course not be included in the test suite in a more direct manner, and a tool to
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convert files from ClassicTIFF to BigTIFF, as well as the other way around for
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source BigTIFF files that do not exceed 4 gigabyte in size.</p>
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<p>Frank Warmerdam has also agreed to be involved in a consulting and validation
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role. Frank has been LibTiff's primary maintainer since approximately the year
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2000, develops large-image exploitation software for the geospatial industry
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(GDAL) and is currently President of the Open Source Geospatial Foundation
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(OSGeo). Frank will also be ensuring that BigTIFF improvements are made
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accessible to all users of the GDAL library.</p>
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<h2>3. Implementation Strategy</h2>
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<p>Many people who have a need for BigTIFF, use LibTiff already. We thus plan to
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support BigTIFF in LibTiff, applying a minimum change strategy much like the
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one that was applied in the creation of the new file format in the first
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place.</p>
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<p>To support BigTIFF, we will use a 64bit integer datatype. It is anticipated
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that some older platforms will not be able to comply with this need, and for
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that reason we will encapsulate all required changes inside a conditional
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compilation switch.</p>
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<p>While it is anticipated that there will be ABI (application binary interface)
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changes as part of a BigTIFF support upgrade to LibTiff, and possibly some
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more to support other major upgrades to LibTiff, the plan is such that
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the source level API will remain compatible for most LibTiff applications.
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Applications using specialized interfaces may require some minor source code
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changes, but we will provide backwards compatibility to support the majority
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of existing application level code.</p>
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<p>The resulting LibTiff version would transparently support reading traditional
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32bit ClassicTIFF files, and 64bit BigTIFF files, as well as writing either
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ClassicTIFF or BigTIFF files based on a flag in the TIFFOpen/TIFFClientOpen call.</p>
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<h2>4. Intellectual Property and Licensing</h2>
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<p>The licensing agreement of LibTiff will remain unchanged.</p>
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<h2>5. Contact information</h2>
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<p>Please contact <a href="mailto:warmerdam@pobox.com">Frank Warmerdam</a> and/or
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<a href="mailto:info@awaresystems.be">Joris Van Damme</a> for more information
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on sponsorship agreements.</p>
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