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From: eeidson@eng.AUburn.EDU (Eric Eidson)
Newsgroups: comp.windows.x
Subject: Re: Displaying GIF pictures under X windows
Message-ID: <9011290832.AA08030@eng.auburn.edu>
Date: 29 Nov 90 08:32:51 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 47

In <1990Nov29.031653.28066@boingo.med.jhu.edu>, David Heath writes:

|> >From reading the compuserv GIF documentation, I was under the impression
|> the GIF standard was meant to be easily extensible. Software written for
|> old versions of the standard would just ignore blocks that they didn't
|> understand. If this is so, they WHY do so many programmers who write
|> GIF readers insist on checking for "GIF87a" in the header? This seems
|> incredibly short sighted to me.

|> If there is a good reason for this, I would like to hear it.

The only reasons that I can think of is:

a)  It's the easiest way to make sure that it is a gif format file...wouldn't 
	want to read a MACPaint file as a GIF, would we?

b)  I only know of two GIF formats, gif87a and gif89a.  Since most of the 
	programs were written before gif89a was released for designers, why
	would anyone NOT use it to check to see if the file was a GIF???

I don't mean for the above to sound rude.  You are right, the GIF format was
designed to be easily extensible from what I remember reading.  But when 
programmers weren't sure that there was ever going to be a new and improved 
format, that would just be an extension of the current format, why bother with
programming in extensibility when the programmer would not be sure what needed
extended?  Furthermore, if the new format was just an extension of the old 
format, isn't the only thing needed to handle the new block (the ones you are
currently ignoring) to add the pertinant code.

So, it's not really a good reason, I just can't think of a good reason not to
do it that way...

--------------------
The above is just the way I understood the situation... 
If I'm wrong, tell me... Send me any comments, corrections (likely), flames, 
praises (doubtful), etc...

Hunter Eidson

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