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Date: Fri, 10 Jul 1998 08:39:31 -0400
Subject: Citable, true specification for PackBits?
To: tiff@sgi.com
From: d_smith@ecrm.com (Dan Smith)
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Question (1): What text do we include if we want to reference 
"the TIFF spec?" "TIFF Revision 6.0, Final - June 3, 1992,
Aldus Developers Desk, Aldus Corporation, 411 First Avenue,
South Seattle, WA 98104-2871, CompuServe: GO ALDSVC, 
Message Section #10, Applelink: Aldus Developers Icon
For a copy of the TIFF 6.0 specification, call (206) 628-6593"
does not seem very useful! (I guess Seattle is still around, but
neither Aldus, CompuServe, nor AppleLink is). Does a TIFF
support organization still exists within Adobe? Does anyone know
the correct text with which to replace the above?

Question (2): Is there a clean specification for PackBits anywhere
that we can include or reference?  The description in the TIFF
spec ("Use the Toolbox routines... pseudocode to do it
_might_ look like this... it is _best_ to... that is the _essence_
of the algorithm... here are some _additional_ rules") is not,
IMHO, a real spec.  If someone writes what they think is
PackBits-compressed data and we don't unpack it properly,
we want to know which party needs to revise their code, not
get into spirited discussions along the lines of "but you
didn't say we _had_ to do that, you just said it was _best_."

My company makes a hardware product (a SCSI controller for our
imagesetters) that, among other things, has built-in hardware
PackBits decompression) and we're in the process of reviewing
the documentation for it.  I believe that this documentation really
ought to specify _exactly_ what we mean by "PackBits decompression,"
either by including a true specification of the decompression scheme
itself, or by including a usable reference to a true specification...

(BTW I get the Apple Developer CD's and am unaware of anything
suitable in the Technical Notes... Can anyone point me to
a real Apple spec, not just another chatty "try this, watch out 
for that" discussion?) (Also, I do understand that PackBits is pretty
simple and you can PROBABLY code to the informal notes in the TIFF
spec and not go wrong.  But I don't feel OUR specification can
just say "Hey, D00D, just do it--everyone knows how PackBits works,
you shouldn't have any problems unless your head is screwed on wrong.")


