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From: rg@msel.unh.edu (Roger Gonzalez)
Newsgroups: comp.graphics,comp.compression
Subject: Re: gif encoding questions
Message-ID: <1991Apr11.213950.16265@unhd.unh.edu>
Date: 11 Apr 91 21:39:50 GMT
References: <1991Apr9.142255.186@unhd.unh.edu> <1991Apr10.095103.26252@ukpoit.co.uk>
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>In article <1991Apr9.142255.186@unhd.unh.edu> I write:
>>Why have I seen gray scale (256) GIFs that don't have simple color maps like
>>00 00 00 01 01 01 02 02 02 03 03 03 ... FE FE FE FF FF FF
>>
>>Some of them are really strange...

But what I meant was: 
When looking at grayscale 256 GIFs, I would expect
>>00 00 00 01 01 01 02 02 02 03 03 03 ... FE FE FE FF FF FF
but have seen (in ppmtogif results, for example)

000000   47-49-46-38-37-61-00-02   00-02-E7-00-00-00-00-00   GIF87a@B@B.@@@@@
000010   C9-C9-C9-8F-8F-8F-55-55   55-1B-1B-1B-E4-E4-E4-AA   ......UUU[[[....
000020   AA-AA-70-70-70-36-36-36   FF-FF-FF-C5-C5-C5-8B-8B   ..ppp666........
000030   8B-51-51-51-17-17-17-E0   E0-E0-A6-A6-A6-6C-6C-6C   .QQQWWW......lll
000040   32-32-32-FB-FB-FB-C1-C1   C1-87-87-87-4D-4D-4D-13   222.........MMMS

And I was wondering why the screwy ordering.  Sorry if I wasn't clear.

I've been trying to reverse engineer what my problems are with my
encoder by comparing my output with the results of rawtopgm | ppmtogif,
but my comparison can only go so far before I hit a root code that 
is different that mine because their greyscale map is different.

Why am I writing my own encoder when I could swipe code from everyone else?
'Cause I'm a masochist.  So what if its a memory pig, I don't use hashing 
yet, and its slower than shit?  I'm having fun!  

If you are equally masochistic, and would like to give me a hand, my
almost-but-not-quite encoder is on msel.unh.edu in /pub/gif for ftp-ing.

I'm really close.. I get one good scan line out (using VUIMAGE on a
PC), and then a shitty scan line, and then it stops. I think it barfs
because I don't change bit sizes where it expects me to.  Sigh.

-Roger
-- 
"The question of whether a computer can think is no more interesting
 than the question of whether a submarine can swim" - Edsgar W. Dijkstra 
rg@[msel|unhd].unh.edu        |  UNH Marine Systems Engineering Laboratory
r_gonzalez@unhh.bitnet        |  Durham, NH  03824-3525