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Concept
GIF
Summary
The Graphics Interchange Format (GIF; ɡɪf or dʒɪf , see pronunciation) is a bitmap that was developed by a team at the online services provider CompuServe led by American computer scientist Steve Wilhite and released on June 15, 1987. It is in widespread usage on the World Wide Web due to its wide support and portability between applications and operating systems.
The format supports up to 8 bits per pixel for each image, allowing a single image to reference its own palette of up to 256 different colors chosen from the 24-bit RGB color space. It also supports animations and allows a separate palette of up to 256 colors for each frame. These palette limitations make GIF less suitable for reproducing color photographs and other but 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 file size without degrading the visual quality.
CompuServe introduced GIF on 15 June 1987 to provide a color image format for their file downloading areas. This replaced their earlier run-length encoding format, which was black and white only. GIF became popular because it used Lempel–Ziv–Welch data compression. Since this was more efficient than the run-length encoding used by PCX and MacPaint, fairly large images could be downloaded reasonably quickly even with slow modems.
The original version of GIF was called 87a. This version already supported multiple images in a stream.
In 1989, CompuServe released an enhanced version, called 89a, This version added:
support for animation delays
transparent background colors
storage of application-specific metadata
allowing text labels as text (not embedding them in the graphical data). As there is little control over display fonts, however, this feature is rarely used.
The two versions can be distinguished by looking at the first six bytes of the file (the "magic number" or signature), which, when interpreted as ASCII, read "GIF87a" or "GIF89a", respectively.
Official source
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