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a. a standard compressed file format used for pictures
b. a picture held in this format
GIF(Graphics Interchange Format) A popular bitmapped graphics file format developed by CompuServe. Pronounced "jif" or "gif" (hard g), GIF images are widely used on the Web because the format is compressed and takes up less space.
GIF supports 8-bit color (256 colors), but it gets the most mileage out of its limited colors by using a built-in color palette. For example, the palette for an image of a forest would mostly contain shades of green and brown. If all the colors in the image are within a tight range, GIFs provide excellent realism for an 8-bit format. In contrast, JPEGs are 24 bits. See indexed color.
GIF87a and GIF89a
The original GIF87a and subsequent GIF89a are named after their year of introduction. GIF89a allows one of the colors to be transparent and reflect the background color of the underlying page or window (see alpha channel). GIF89a also supports a limited form of animation by rendering multiple frames in sequence (see animated GIF).
GIFs and JPEGs
Both GIF and JPEG images are widely supported on the Web. Charts, screen shots and technical drawings are typically GIFs, because GIFs use lossless compression, and the text is maintained properly. Photos are generally better rendered as JPEGs, which support 24-bit color, and they can be highly compressed. However, if images are saved as JPEGs with limited compression (users have a choice), text does render rather well (see JPEG). See GIF patents, lossless compression, graphics formats and PNG.
|More Shades Than Apparent|
|At first glance, it looks like the Android robot logo is only green, white and black. Zooming into one of its antennas shows more shades (see dithering).|
|Even More Colors|
|The GIF format picks the 256 most used colors in an image. Notice how the colors in the palettes match the two images.|