GIFGIF, which stands for Graphics Interchange Format, is widely used for transmission of images across data networks. Introduced by CompuServe Information Service in 1987, it is supported by all web browsers making it a very popular format.
GIF displays a maximum of 256 colors, which makes it unsuitable for pictures with continuous colors. Its application is best for color clip art, black-and-white line drawings, or images with large blocks of solid colors. Other uses of GIF include images with transparent areas, colors in detached areas, buttons on sites, small icons, images containing texts, and animations.
The compression algorithm used in GIF is LZW, or Lempel Ziv Welch, which is a lossless compression/decompression scheme. This technique reduces the file size without diminishing its visual quality. The GIF file is stream-based, which means that it is composed of blocks, or data packets, each containing a separate set of information. These blocks are often divided into sub-blocks each containing additional data. Together these blocks and sub-blocks define the method to be used in the reproduction of the image.
There are two versions of the GIF format – 87a (the one first introduced in 1987), and 89a. The second version was introduced in 1989 (as the name implies) and allows the image to be animated. It is this format that is used for animations, which is actually a sequence of images in a single GIF file. It is best to have a system that supports both 87a and 89a versions, as the older version is still in use. A system that supports only one version, will not support the other.
GIF is supported by all software applications that read and write graphical image data, and can be used on various platforms like MS Dos, Macintosh, UNIX, and Amiga. The maximum image size produced by a GIF file is 64K X 64K pixels.
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