Message-ID: 4.2.0.58.20000229135702.01f39c10@icarus.com
To: tiff@olympiakos.com
Subject: Re: Tiff verification utility
From: "Louis H. Sharpe II" <lsharpe@picturel.com>
Date: Tue, 29 Feb 2000 14:55:02 -0700
In-Reply-To: <80256893.0056EFD2.00@apollo3.kainos.com>
Sender: owner-tiff@olympiakos.com


At 2/28/00 03:54 PM+0000, Neal Gordon wrote:

  > Does anyone know if there is a program, or publically available
  > algorithm which will allow me to generate a checksum for tiff images?

Message digests (such as MD5) are superior to checksums since they change 
in response to byte swaps. There is some (nearly) public code at:

   http://theory.lcs.mit.edu/~rivest/md5.c

We have run this on TIFF files and stored the results externally to the 
TIFF files.

If the community wanted a tag for this value, we would have to register a 
tag and define some rules for its use. What bytes would be included in the 
calculation? Image bytes only or the full file (except that's 
self-referential)? I guess it could be the whole file minus the n reserved 
bytes occupied by the fixed-length MD5 ASCII-encoded result string.

Lou
Picture Elements, Inc.



