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Date: Thu, 11 Oct 2012 17:20:59 -0500 (CDT)
From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us>
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Cc: tiff@lists.maptools.org
Subject: Re: [Tiff] TIFFTAG_EXIFIFD tag type change in libTIFF 4.0.x?
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On Thu, 11 Oct 2012, Andrew Pangborn wrote:

> Hi,
>
> I have recently started working on migrating from libTIFF 3.9.5 to
> 4.0.3. I was running some regression testing on image metadata for my
> platform and ran into some snags with EXIF. Specifically, it looks
> like the tag type in tif_dirinfo.c for TIFFTAG_EXIFIFD was changed
> from TIFF_LONG to TIFF_IFD8. When writing a TIFF the file ends up with
> tag type 13 (TIFF_IFD) for TIFFTAG_EXIFIFD. Unfortunately our EXIF
> parser expects the EXIFIFD offset to be of tag type 4 (LONG) and
> doesn't follow the offset to the subifd.
>
> The following both specify that it should be type LONG

Without even looking into this issue, I should mention that due to 
libtiff 4 supporting the new BigTIFF format (supports huge files via 
64-bit offsets), offsets are now produced/consumed as 64-bit unsigned 
types.  Functions which now return a 64-bit type may also return an 
error code as -1 cast to the 64-bit unsigned type so it is very 
important that the return type size is 64-bit unsigned or else error 
handling won't work right (i.e. don't accidentially assign to a 32-bit 
value).  These are the main changes to the previously existing libtiff 
API.

See the text associated with the 4.0.0 release at 
"http://www.remotesensing.org/libtiff/v4.0.0.html".

Bob
-- 
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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