Table of Contents
GIFLIB is a package of portable tools and library routines for working with GIF images.
The Graphics Interchange Format(c) specification is the copyrighted property of CompuServe Incorporated. GIF(sm) is a service mark property of CompuServe Incorporated.
This package has been released under an X Consortium-like open-source 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. 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.
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.
display images saved as GIF files under X window system.
assemble multiple GIFs into one, or burst a multiple-image GIF
clip or crop a GIF image
modify GIF image colormaps
combine 2 GIF images of exactly the same size into one
clumsily attempts to fix truncated GIF images
flip GIF image along X or Y axis or rotate by 90 degrees
convert between interlaced and non interlaced images
generate one composite GIF from a multiple-image GIF
change a GIF's screen size or recondition it.
rotate a GIF through any desired angle
resize a GIF by deletion or duplication of bits
converter/deconverter to/from an editable text format
generate GIF images out of regular text in 8x8 font
end-of-pipe fitting for GIF-processing pipelines
use giflib tools to compose images
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.
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 extremely memory-limited machine 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 doc subdirectory includes flat-ASCII descriptions of GIF89 format and Lempel-Ziv Compression.
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.