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What Is the Graphics Interchange Format?

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  • Written By: Robert Grimmick
  • Edited By: R. Halprin
  • Last Modified Date: 14 April 2014
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The Graphics Interchange Format (GIF) is a computer file format used for images and simple animation. It was developed by CompuServe® in the late 1980s and grew in popularity with the proliferation of the Internet. GIF is a bitmap format supporting up to 256 colors and a form of lossless compression that decreases file size without a loss in image quality. GIFs became a source of controversy in the mid-1990s when a company tried to enforce a software patent related to collecting licensing fees.

File formats dedicated to pictures and images have existed since computers first became capable of displaying them. As technology has evolved, new formats have been created to add new capabilities. Specifications for the graphics interchange format were first released in 1987 by CompuServe®, a U.S. Internet service provider. Prior to this, most image formats were limited to black and white and were not optimized for transmission over the Internet.

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GIF was the first image format to be widely supported by web browsers, and has remained popular online despite the introduction of newer formats. The GIF format isn’t particularly well suited to photographs since it can only support 256 colors, but it can deliver both clarity and efficiency for simpler images like illustrations or logos. The second revision of the format, GIF89a, supports transparencies. One fairly unique feature of the graphics interchange format is support for animation. Multiple GIF images can be saved within a single file and played back in sequence, much like a roll of film in a movie projector.

Images created using the graphics interchange format are saved in what is known as a raster or bitmap image format. This means the format contains information describing the width and height of the image and where individual pixels belong in that image. The other type of image format, vector graphics, saves images in a mathematical format that describes how an image should be drawn on a screen. Vector images, unlike bitmaps, can be resized without a loss in quality, but are much more computationally intensive.

Like many of the image and graphics file formats used on the Web, GIFs are compressed to reduce file size and enable faster transmission over the Internet. Some formats, such as the Joint Photographic Experts Group (JPEG) format, use lossy compression, which reduces the image’s file size by decreasing image quality. The graphics interchange format uses a form of lossless compression called Lempel-Ziv-Welch (LZW), named for the three men who developed the technique. LZW compression utilizes a mathematical algorithm to compress and decompress data within a file, thereby resulting in smaller file sizes without any loss of quality.

The use of GIF images became controversial when it was revealed that the format was subject to a software patent owned by information technology company Unisys®. The patent did not apply to the image format itself, only the LZW compression that GIF used. Unisys® announced in late 1994 that it expected those using LZW compression, whether for GIF images or other file formats, to pay a licensing fee. Some web masters feared the company would try and collect royalties from any website using GIFs, and the Portable Network Graphics (PNG) format was created as a patent-free alternative. PNG images did not become the immediate success some had hoped; in 2003 the Unisys® patent on LZW expired, meaning that both formats can now be used freely.

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