GIFencoding

GIF encoding refers to the process of converting raster images or sequences of images into the Graphics Interchange Format (GIF), a bitmap image format introduced by CompuServe in 1987. GIF uses a palette-based color model and supports animation by encoding multiple frames in a single file, each with timing and disposal instructions. Typical GIFs use 8 bits per pixel, allowing up to 256 colors per frame.

Encoding process: first, color quantization reduces the source image to a palette of up to 256 colors. This palette can be global (shared by all frames) or local (per frame). Each source pixel is replaced by the index of its closest color in the chosen palette, optionally with dithering to preserve image detail. The resulting index data is then compressed using Lempel-Ziv-Welch (LZW) compression to form the image data blocks.

GIF structure supports features: the file begins with a header 'GIF87a' or 'GIF89a'; a logical screen descriptor; optional global color table; then one or more image blocks representing frames, each with an image descriptor and local color table if used. Extensions provide functionality such as transparency (a transparent color index), user-defined delays between frames, loop counts (e.g., infinite looping via Netscape application extension), and disposal methods that describe how the next frame should be drawn.

Limitations and usage: GIF is well-suited for simple graphics, line art, and small animations, with strong support for transparency and predictable color handling. It is less suitable for detailed photographic images due to the 256-color limit per frame. Alternative formats like PNG or WebP provide higher color fidelity, while GIF remains widely supported across browsers and platforms. Tools and libraries exist to encode GIFs, including general image processing suites and dedicated GIF encoders.

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