29-09-2012, 04:08 PM
Graphics Interchange Format
ABSTRACT
The Graphics Interchange Format (GIF) is a bitmap image format that was intro-
duced by CompuServe in 1987 and has since come into widespread usage on the World
Wide Web due to its wide support and portability.
The format supports up to 8 bits per pixel thus allowing a single image to reference
a palette of up to 256 distinct colors. The colors are chosen from the 24-bit RGB color
space. It also supports animations and allows a separate palette of 256 colors for each
frame. The color limitation makes the GIF format unsuitable for reproducing color
photographs and other images with continuous color, but it is well-suited for simpler
images such as graphics or logos with solid areas of color.
GIF images are compressed using the Lempel-Ziv-Welch (LZW) lossless data
compression technique to reduce the ¯le size without degrading the visual quality. This
compression technique was patented in 1985. Controversy over the licensing agreement
between the patent holder, Unisys, and CompuServe in 1994 spurred the development of
the Portable Network Graphics (PNG) standard; since then all the relevant patents have
expired. If multiple images are stored within a GIF ¯le, they can be viewed sequentially
much like a slide show or a small animated movie. The way they appear is de¯ned by
control extensions built into the ¯le. With the appropriate tools, such as Ulead GIF
Animator