案例库 · 软件与 IT · 技术决策 · 1990–1996
这条还没译成中文，下面是英文原文。
Deflate became the web's compression because it was published free, not patented.
Phil Katz's LZ77+Huffman scheme was released as an open RFC, so ZIP, gzip, zlib and PNG used it freely, while the patented LZW in GIF was enforced.
PKWARE · Phil Katz · the IETF
那一手
In the early 1990s the dominant lossless method, LZW (used by Unix compress and by GIF), sat behind a Unisys patent, US 4,558,302. LZW-based compress even disappeared from many Unix distributions because of the patent and because gzip beat it on ratio.
Phil Katz's Deflate, shipped in PKZIP 2 in 1990, paired LZ77 string back-references with entropy-coded Huffman trees. He patented his encoder but published the Deflate format as RFC 1951, describing a stream any implementer could produce.
That separation mattered: the Deflate format could be used without a licence. In 1993-94 Unisys moved to enforce licensing fees on LZW in GIF, which pushed the market toward patent-unencumbered formats and helped create PNG, which uses Deflate.
The result was that Deflate, not LZW, became the web's default compression and lives on in ZIP, gzip, zlib, PNG and PDF, whose default is Deflate rather than LZW.
为什么管用
- LZW compression was ring-fenced by a Unisys patent that its owner later enforced
- Publishing the Deflate format as an RFC made implementing it licence-free
- A free format was a safe default for developers navigating the patent mess
- gzip beat compress on ratio as well, so switching was beneficial, not just safe
可以搬走什么
If you can split the format from the encoder, give the format away: a royalty-free spec captures the whole market, while keeping the patent on your particular implementation.
后来呢
Deflate became the basis of gzip, zlib, PNG and the ZIP archive, and is the default compression used inside PDF for much text data. Unisys's LZW patent expired in the US in June 2003, but by then the free Deflate format had already won the default slot.
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