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March 2005
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2005.03.17 03:53 "Re: libtiff and EXIF", by Bob Friesenhahn
On Thu, 17 Mar 2005, Ron wrote: > I've been looking at what is required to parse exif data using libtiff, > and it looks like surprisingly little. It was trivial to bypass enough > sanity checks to easily get it to recognise and read the ExifIFD and > auto register all the tags it found there. And not that much harder to > get it to recognise a similar tiff'ette extracted from the APP1 section > of a jpeg file with exif data and then fed to libtiff. > > So the biggest question is how you all feel about supporting this from > libtiff. Obviously TIFFFieldInfo for exif tags, if people wanted them, It is intended the libtiff support it, or at least cleanly allow it. I was about to dive into this myself. Please post a clean patch against the libtiff CVS version to libtiff's bugzilla at "http://bugzilla.remotesensing.org/enter_bug.cgi?product=libtiff". That should hasten getting some support into libtiff. > could be cleanly separated from the main lib, so the main issue would be > how to provide the necessary functions for generic IFD handling. > (generic tags are already handled beautifully) > > The easy way is to just provide some alternative functions, that (ab)use > the existing structures as my proof of concept does, without the > operations that are specific to valid .tif, but not found in exif > data. The harder, but long term more rewarding way, would be to factor > out a generic IFD interface, and reimplement the strictures of TIFF vX.Y > on top of that. Harder because it probably means breaking the ABI (at > least) to split common parts out of existing structures -- which is a > pretty extreme step to add support for something not strictly tiff but > might be justified in other ways all the same. Perhaps this can be a task for libtiff 4.0. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/