I personally wrote an implementation of lzw in Assembly in my late teens. It could deal with gifs... that was before 1999, when Unisys[0] claimed the patent (f

I personally wrote an implementation of lzw in Assembly in my late teens. It could deal with gifs... that was before 1999, when Unisys[0] claimed the patent (for all kind of uses) and had the patent for many a year, PNG was created not to use lzw since it was patented. The algorithm was patented for the encoding part but not decoding. [0]: https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Signal_Processing_and_Modeling/Information_and_Entropy_(Penfield)/03%3A_Compression/3.05%3A_Dynamic_Dictionary/3.5.01%3A_The_LZW_Patent https://eng.libretexts.org/Bookshelves/Electrical_Engineerin...