Steve Blackstock explains the Lempel-Ziv Welch (LZW) compression algorithm used in GIF files. LZW compresses data by recognizing repeated strings. In compression, the charstream becomes the input, and the codestream is the output. In decompression, the reverse happens. The GIF variation introduces special codes like clear code and end-of-information for efficiency. The compression size changes dynamically during encoding and decoding. The initial table includes root codes and two special codes. Variable compression sizes are managed by adjusting the bit length. The packaging of codes in the codestream must align with the lowest available bit. Understanding LZW and its GIF variations is key to mastering this compression technique.
https://www.eecis.udel.edu/~amer/CISC651/lzw.and.gif.explained.html