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by M.I.T. but is also freely distributable. It appears that
the arithmetic coding option of the JPEG spec is covered
by patents owned by IBM, AT&T, and Mitsubishi. Hence
arithmetic coding cannot legally be used without obtaining
one or more licenses. For this reason, support for arithmetic
coding has been removed from the free JPEG software.
(Since arithmetic coding provides only a marginal gain over
the unpatented Huffman mode, it is unlikely that very many
implementations will support it.) So far as we are aware,
there are no patent restrictions on the remaining code. The
IJG distribution formerly included code to read and write GIF
files. To avoid entanglement with the Unisys LZW patent,
GIF reading support has been removed altogether, and the
GIF writer has been simplified to produce "uncompressed
GIFs". This technique does not use the LZW algorithm; the
resulting GIF files are larger than usual, but are readable by
all standard GIF decoders. We are required to state that "The
Graphics Interchange Format(c) is the Copyright property
of CompuServe Incorporated. GIF(sm) is a Service Mark
property of CompuServe Incorporated."
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