GIF - Data Compression

Apart from reducing the number of colours, GIF uses common entropy coding to get further compression. A slightly modified version of the LZW algorithm will be applied.

LZW is a lossless compression method suitable for arbitrary data. The abbreviation stands for Lempel-Ziv-Welch designating the inventor Terry Welch and the basic work of Abraham Lempel and Jacob Ziv.

The used data compression algorithm is characterised by its ability to compress recurring sequences of pixels effectively.

At run-time a sequence table is developed reflecting the already encoded part of the picture. Instead of the colour information, indices to this table will be used. The compression effect arises if longer sequences are already contained in the table.

This algorithm is particularly effective with simple graphics, technical drawings, sketches or diagrams. Photo-realistic representations or high definition pictures are not suited for this format.