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From: ken@watsun.cc.columbia.edu (Ken Rossman)
Newsgroups: comp.graphics
Subject: Re: GIF for the Mac. How? (Please Help!)
Message-ID: <2544@cunixc.cc.columbia.edu>
Date: 21 Dec 89 20:30:36 GMT
References: <8731@amherst.bitnet>
Sender: news@cunixc.cc.columbia.edu
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In-reply-to: KSBOLDUAN@amherst.bitnet's message of 16 Dec 89 12:09:12 GMT


  I've found lots of archives that have GIF files, but none of them are in
  .hqx format. I FTP from my VAX and then download to my Mac. I tried to do
  this with some of the GIF files, but it wouldn't work unless they were
  binhexed first.

I've run into this also.  I've been trying to move GIFs back and forth
between some Suns here and some Mac II's, with little success so far.

  Am I mistaken or is a GIF a GIF a GIF regardless of what machine you want
  to view them on (IBM, MAC, AMIGA etc.) ?

Well, I've run into a couple of problems so far with the idea that "GIF is
GIF no matter where you are".  One problem that you definitely have to
watch out for, and this is the case with any binary file, is the method of
file transfer.  You have to somehow tell the program you are using not to
do any funny transformations in the transfer (like CRLF's to CR's, or LF's
to CRLF's, etc).

The other thing that ought not to matter really, but sometimes does,
depending on how the translation code is written, is the problem of byte
ordering across different machine architectures.  You mentioned in your
letter both Mac's and VAXen.  They stuff bytes in words in a different
order.  I can never remember which is which, but one is called "big
endian", and the other is "little endian".  The difference is whether the
most significant byte comes first in the word or the least significant byte
comes first.

Problems arise here when the image translating code tries to operate on
data items larger than a byte.  If the code operates on a word at a time,
then bytes can be reversed when moving data from a VAX to a Mac, for
example.  I'm still trying to figure out if this is what happened to some
images that got fouled in transfer here.  But I'm no Mac hacker, and that's
where the images are failing now...  sigh...

Ken Rossman
Computer Center
Columbia University
ken@columbia.edu
ken@cunixc.bitnet
...!rutgers!columbia!ken