AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

1998.07.10 12:39 "Citable, true specification for PackBits?", by Dan Smith

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.")