GIFLIB is a package of portable tools and library routines for working with GIF
images. You can find the latest version at the GIFLIB home page
http://www.ccil.org/~esr/giflib.

 The Graphics Interchange Format(c) specification is the copyrighted property of
CompuServe Incorporated. GIF(sm) is a service mark property of CompuServe
Incorporated. As this package existed before UniSys's lawyeritis attack of New
Years' Day 1995, it is grandfathered in under their license terms and you do not
have to pay fees for using it.

 This package has been released under an X Consortium-life freeware license. Use
and copy as you see fit. If you make useful changes, add new tools, or find and
fix bugs, please send your mods to the maintainers for general distribution.

 The util directory includes programs to clip, rotate, scale, and position GIF
images. It includes an X11 viewer, code to dump GIFs to an Epson-compatible
printer in graphics mode, and many conversion utilities. These are no
replacement for an interactive graphics editor, but they can be very useful for
scripted image generation or transformation.

 The library includes program-callable entry points for reading and writing GIF
files, an 8x8 utility font for embedding text in GIFs, and an error handler. GIF
manipulation can be done at a relatively low level by sequential I/O (which
automatically does/undoes image compression) or at a higher level by slurping an
entire GIF into allocated core.

 This library speaks both GIF87a and GIF89. The differences between GIF87 and
GIF89 are minor: in the latter, the interpretation of some extension block types
is defined. The library never needs to actually interpret these, but giftext
notices them.


Utilities

Here is a summary of the utilities in this package. If you're looking at this
page through a web browser, each utility name should be a hotlink to HTML
documentation.


Conversion Utilities


 gif2bgi
 display GIFs on IBM PC displays using the BGI (Borland) driver
 gif2epsn
 dump images saved as GIF files on Epson type printers
 gif2herc
 display GIFs on IBM PC displays using the Hercules graphic card
 gif2iris
 display GIFs under SGI NeWs window system
 gif2ps
 print GIF file on laser printers supporting PostScript
 gif2rgb
 convert images saved as GIF to 24-bit RGB image(s)
 gif2rle
 convert images saved as GIF to RLE (Utah raster toolkit) format
 gif2x11
 display images saved as GIF files under X window system
 raw2gif
 convert raw 8-bit image data into GIF files
 rgb2gif
 convert 24 bit images to a GIF image using color quantization
 rle2gif
 convert images saved as RLE (Utah raster toolkit) to GIF format

 Test Pattern Generators


 gifbg
 generate a single-color test pattern GIF
 gifcolor
 generate color test patterns
 gifwedge
 create a test GIF image resembling a color monitor test pattern

 Image Manipulation Components


 gifasm
 assemble multiple GIFs into one, or burst a multiple-mage GIF
 gifclip
 clip or crop a GIF image
 gifclrmp
 modify GIF image colormaps
 gifcomb
 combine 2 GIF images of exactly the same size into one
 giffix
 clumsily attempts to fix truncated GIF images
 gifflip
 flip GIF image along X or Y axis or rotate by 90 degrees
 gifinter
 convert between interlaced and non interlaced images
 gifovly
 generate one composite GIF from a multiple-image GIF
 gifpos
 change a GIF's screen size or recondition it.
 gifrotat
 rotate a GIF through any desired angle
 gifrsize
 resize a GIF by deletion or duplication of bits
 gifburst
 burst a GIF image into subrectangles.

 Report Generators


 giftext
 print (text only) general information about a GIF
 gifhisto
 generate color-frequency histogram from a GIF

 GIF Composition Tools


 icon2gif
 converter/deconverter to/from an editable text format
 text2gif
 generate GIF images out of regular text in 8x8 font
 gifinto
 end-of-pipe fitting for GIF-processing pipelines
 gifcompose
 use giflib tools to compose images

 C Code Templates


 giffiltr
 template code for filtering a GIF sequentially
 gifspnge
 template code for filtering a GIF with in-core operations


Under MS-DOS, most filters will print the current input scan line number
(counting up) whenever they read image input, and will print output image line
number (counting down) when they dump output. Utilities that only read or write
always print in increasing order. Utilities (like GifPos that only change
positions) that copy the image as a block of compressed data will print nothing
--- they cannot identify a scan line number, and are enough faster that the
feedback to the user doesn't seem necessary.

 Some of the utilities require memory on the order of the whole screen, while
others read one scan line at a time. Each utility HTML file has entry called
Memory Usage which will be one of:




 Line
 memory required is on the order of one scan line
 Image
 proportional to the size of the biggest image in GIF file
 Screen
 proportional to GIF screen size


In all cases a byte is allocated per pixel, so an image of 320 by 200 pixels
will requires approximately 64k bytes of main memory.


Library Functions

The library contains two groups of C functions. One group does sequential I/O on
the stream-oriented GIF format. The other supports grabbing an entire GIF into
allocated core, operating on it in core, and then writing the modified in-core
GIF out to disk.

 Unless you are on a 286 or some other very memory-limited machine running under
DOS, you probably want to use the second group.

 Detailed documentation on the library entry points is in gif_lib.html. Library
error codes are described in liberror.html


The GIF Standard

The doc subdurector includes flat-ASCII descriptions of GIF89 format and
Lempel-Ziv Compression.


History

This package was originally written by Gershon Elber in 1990 on an IBM PC under
MS-DOS using Borland Turbo C. He made it portable to several UNIX environments.

 The 2.1 version featured substantial changes and additions by Eric S. Raymond .
These included the DGifSlurp/EGifSpew function pair for enabling non-sequential
operations on GIF images and the tools icon2gif, gifovly, gifburst, and
gifcompose.

 The 2.4 version converted all the docs from an idiosyncratic plain-text formal
to to HTML.


Package Status

GIFLIB's current maintainer is Eric S. Raymond. You can find his home page at
http://www.ccil.org/esr.

 GIFLIB is not under active development, but bug fixes are being accepted.