koreth@ssyx.ucsc.edu (Steven Grimm) (04/21/88)
I have gotten lots of requests for the GIF file format since I posted some
GIF pictures to rec.arts.startrek. Here's a document describing what GIF
files look like. I'm crossposting this article to several groups, so keep
that in mind when following up. It is a uuencoded and compressed text file.
-Steve
-----------* cut here *------------
begin 600 GIF.DOC.Z
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endjensen@gt-eedsp.UUCP (P. Allen Jensen) (05/14/88)
Where can I get a detailed description of the GIF format ?
--
P. Allen Jensen
Georgia Tech, School of Electrical Engineering, Atlanta, GA 30332
USENET: ...!{allegra,hplabs,ihnp4,ulysses}!gatech!gt-eedsp!$me
INTERNET: $me@gteedsp.gatech.edujohnm@trsvax.UUCP (05/16/88)
> Where can I get a detailed description of the GIF format ? > -- > P. Allen Jensen On CompuServe "GO PICS" to get to the GIF area and you will find the specification in Download Area 1. John Munsch
greg%pipe@gatech.edu (Greg Williams) (02/04/89)
I have recently been getting a lot of GIF picture files, and I was wondering if anybody could tell me exactly what the format of a GIF file is. I want to eventually write my own GIF file viewer, and I need to know what the file looks like. Send replies to ccastgw@prism.gatech.edu greg@pipe.gatech.edu GREG WILLIAMS "Barbaric Penguin" Disclaimer: The usual stuff.
ian@media.UUCP (Ian Poynter) (02/04/89)
I have been asked by someone in our company who does not have access to news
to post this question. Please direct all responses either to me by e-mail
or to comp.graphics, since I don't read comp.sys.ibm.pc.
Thanks.
The following is an excerpt from the GIF image format specification:
SCREEN DESCRIPTOR
The Screen Descriptor describes the overall parameters for all GIF
images following. It defines the overall dimensions of the image space
or logical screen required, the existence of color mapping information,
background screen color, and color depth information. This information
is stored in a series of 8-bit bytes as described below.
bits
7 6 5 4 3 2 1 0 Byte #
+---------------+
| | 1
+-Screen Width -+ Raster width in pixels (LSB first)
| | 2
+---------------+
| | 3
+-Screen Height-+ Raster height in pixels (LSB first)
| | 4
+-+-----+-+-----+ M = 1, Global color map follows Descriptor
|M| cr |0|pixel| 5 cr+1 = # bits of color resolution
+-+-----+-+-----+ pixel+1 = # bits/pixel in image
| background | 6 background=Color index of screen background
+---------------+ (color is defined from the Global color
|0 0 0 0 0 0 0 0| 7 map or default map if none specified)
+---------------+
Unfortunately, the document does not specify anywhere what is meant by
"Color Resolution." It does not appear to mean what comes to mind, i. e.
color resolution of 0 implying 2 ** 1 colors, 1 meaning 2 ** 2 ...
This poses no problem in reading a GIF file, as all necessary information is
provided elsewhere but it remains unclear what value to enter into this
field when writing out an image.
I would appreciate any clarification I can get.
--
Ian (I answer *all* mail) Poynter Phone: +1 (301) 495-3305
UUCP: ..!{mimsy,sundc}!{prometheus,hqda-ai}!media!ian
Internet: (new) ian%media@pentagon-ai.army.mil (but too new to work?)
(old) ian%media@hqda-ai.arpa (going away real soon now)paulc@hpgrla.HP.COM (@Paul Charlton) (02/08/89)
> Unfortunately, the document does not specify anywhere what is meant by >"Color Resolution." It does not appear to mean what comes to mind, i. e. >color resolution of 0 implying 2 ** 1 colors, 1 meaning 2 ** 2 ... >This poses no problem in reading a GIF file, as all necessary information is >provided elsewhere but it remains unclear what value to enter into this >field when writing out an image. > >I would appreciate any clarification I can get. "pixel + 1" is the number of bits used as a palette index ie: if (pixel == 4), the picture uses 32 colors. the "color resolution" is an indication of how many bits are in each palette slot, for 24 bit color, the "color resolution" is (8 - 1) = 7 for 12 bit color, the "color resolution" is (4 - 1 ) = 3 PaulC { paulc@hpgrai.hp.com } | { hplabs!hpgrai!paulc }
jcocon@hubcap.clemson.edu (James C O'Connor III, 2846) (02/09/89)
From article <4180015@hpgrla.HP.COM>, by paulc@hpgrla.HP.COM (@Paul Charlton): >> Unfortunately, the document does not specify anywhere what is meant by >>"Color Resolution." It does not appear to mean what comes to mind, i. e. >>color resolution of 0 implying 2 ** 1 colors, 1 meaning 2 ** 2 ... >>This poses no problem in reading a GIF file, as all necessary information is >>provided elsewhere but it remains unclear what value to enter into this >>field when writing out an image. >> Does someone have the GIFF format? Please E-mail it to me. Thanks, Jim O'Connor
john@cooper.cooper.EDU (John Barkaus) (03/28/89)
Hi,
I would like information on the format of .GIF files.
If there is any interest, I will post what I find out.
Thanks in advance.
John
John M. Barkaus at the Cooper Union, NY, NY.
INTERNET: john%cooper.cooper.edu@cmcl2.nyu.edu
UUCP: cmcl2!cooper!johndavidsen@steinmetz.ge.com (Wm. E. Davidsen Jr) (03/30/89)
In article <1479@cooper.cooper.EDU> john@cooper.cooper.EDU (John Barkaus) writes: | I would like information on the format of .GIF files. | If there is any interest, I will post what I find out. The GIF standard is in the GIF section of *IX BBS System sixhub (*IX BBS) Phone 518-346-8033 login bbs board mbs area GIF -- bill davidsen (wedu@crd.GE.COM) {uunet | philabs}!steinmetz!crdos1!davidsen "Stupidity, like virtue, is its own reward" -me
macs3440@rocky.oswego.edu (Craig Siegelson) (03/30/89)
Can anyone supply me with a list of systems connected to this
NETwork?
I know the list may be very extensive, but if anyone can mail me a copy
or post me a copy.
Thanx.....
Craig R. Siegelson
macs3440@rocky.Oswego.EDUed@maven.UUCP (Ed Hand) (05/31/89)
Can anyone out there provide me with or point me to a document that defines
the GIF specs? I would greatly apreciate it.
And no, this has NOTHING to do with all the recent er um ah discussions :-).
aTdHvAaNnKcSe
_____________________________________________________________________________
/---\ | ...I may be crazy... | Ed Hand
( o o ) * | ...But it just might be | Intergraph Corp.
\ ^ / *** | a lunatic your looking | b11!maven!ed@Ingr.com
\ ~ / /* | for... | or
---\___/ | Billy Joel | !uunet!ingr!b11!maven!ed
-----------------------------------------------------------------------------cas00772@uxa.cso.uiuc.edu (06/03/89)
ftp to hubcap.clemson.edu .... in the directory pub/gif there is a file
"gif.doc" that explains it as well as can be expected....
-Carycs__sjh@umt.UUCP (Jeffrey Heng) (05/02/90)
Does anyone out there have the specifications of GIF file formats? How many colors is a GIF file able to store? I've used a program to convert GIF files to TARGA-16 files and the converted TARGA-16 files are much , much bigger than GIF files. A friend suggested looking into CompuServe for the GIF file format, but I do not have access to CompuServe. If anyone could post the GIF specifications, it would be greatly appreciated. Thanks.
rosen@polar.bu.edu (David B. Rosen) (05/04/90)
I don't have the GIF Format, but I know why it's smaller: it's
compressed! As I understand it, the GIF file format has LZW (Lempel
Ziv Welch) compression (like unix compress) built in. If you use a
standard compression utility on your TARGA-16 files, they may end up
about the same size as the GIF file (unless TARGA-16 has an internal
structure that would make it relatively incompressible on a
byte-string basis). LZ algorithms are somewhat subtle, but they rely
on the encoder and the decoder each building up the same dictionary of
frequently-occuring strings of arbitrary length, where each string is
represented as a fixed-size codeword (typically 16 bits or less) in
the compressed data stream.
--
David B Rosen, Cognitive & Neural Systems rosen@bucasb.bu.edu
Center for Adaptive Systems Bitnet: rosen%thalamus@buacca
Boston University UUCP: {harvard,uunet}!bu.edu!bucasb!rosen