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Date: Fri, 10 Jul 2009 10:59:01 -0400
From: Gary McGath <gary@hulmail.harvard.edu>
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Subject: Re: [Tiff] TIFFTAG_RICHTIFFIPTC definition
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  "Joris Van Damme \(AWare Systems\)" <info@awaresystems.be> wrote:

>> Please can someone tell me why the TIFFTAG_RICHTIFFIPTC tag is defined as 
>> using type TIFF_LONG? The information is actually an array of bytes not 
>> longs so swapping the bytes if the byte order of the computer and file 
>> differ corrupts the data.
> 
> You're right. This is a historical mistake, and it leads to trouble.
> 
> My humble advice when it comes to writing is using the datatype TIFF_BYTE or 
> TIFF_UNDEFINED. The latter is probably the most 'correct' as it literaly 
> signifies that the data is of mixed type and byte order and widths of data 
> members is defined outside the scope of TIFF. The datatype TIFF_BYTE can be 
> used as amounting to the same thing, though, mostly.

This raises the old issue of verifying a format by the book vs. 
verifying it by "reasonable" usage. JHOVE, by a policy which was set 
from its inception, checks format compliance by the book; thus, 
correcting the data type for TIFFTAG_RICHTIFFIPTC will make JHOVE say 
the file is invalid.

I'm becoming steadily more convinced that by-the-book validation isn't 
the best approach, perhaps especially for TIFF, where Adobe hasn't 
revised "the book" in well over a decade. I've already implemented some 
compromises; this may be one more I should add.

-- 
Gary McGath
Digital Library Software Engineer
Harvard University Library Office for Information Systems
http://hul.harvard.edu/~gary/index.html

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