These are the patents the Netpbm maintainer knows about that relate to
Netpbm.  It is basically just information the maintainer has stumbled
over at some point -- no search has been done.

No licenses have been granted by patent owners to the maintainer of
Netpbm.  Therefore, if you need a patent to use something in Netpbm,
you need your own license.

A note about patents in general: A patent gives an inventor the
exclusive right to make, sell, or use the invention.  If you
independently invent something without knowing that the patent holder
already did, that makes no difference -- the patent holder still has
the exclusive right.  It makes no difference if you give the original
inventor credit.  The patent applies to a method, not its expression,
so writing a program from scratch to implement a certain method is
still a patent infringement.  Infringing a patent is not a crime per
se, but to the extent that it costs the patent holder money, the
infringer has to make it up.

The original purpose of patents is probably perverted when patents are
applied to things you implement in computer programs.  This is one of
the Free Software Foundation's causes.  See 
<http://www.gnu.org/philosophy.html#laws>.

The Jbigtopnm and Pnmtojbig programs use arithmetic coding patents and
other patents covering various aspects of the "front end."


JPEG patents
------------

The Pnmtojpeg and possibly Jpegtopnm programs in some cases may use
the arithmetic coding patents owned by IBM, AT&T, and Mitsubishi.
There is difference of opinion on whether they do.

Forgent owns a patent it believes covers JPEG compression.  This
patent was virtually unknown before July 2002, when Forgent began to
enforce it.  It has successfully enforced it against two companies
(Sony and an unnamed Japanese digital camera maker), but without court
ruling.  This patent, U.S. Patent No. 4,698,672, expires in 2006.

Philips and Lucent Technologies also own patents they claim cover
JPEG.

The following Netpbm components may be restricted by these patents:
Jpegtopnm, Pnmtojpeg, Ppmtompeg, Tifftopnm, Pnmtotiff.  These all
do their JPEG work via a JPEG library not distributed with Netpbm.
Your JPEG-related liability for using Netpbm is limited to your 
liability for using your JPEG library.

Note that it is possible to use Ppmtompeg without involving JPEG and to
build it without the ability to involve JPEG.

The next best alternative to JPEG is probably PNG and maybe JBIG for
bilevel (black and white) images.

http://burnalljpegs.org contains information on this issue.


MPEG patents
------------

The original University of California distributeion of the Ppmtompeg code
conatins this statement in a README file:

  ... patents are held by several companies on various aspects of the MPEG
  video standard.  Companies or individuals who want to develop commercial
  products that include this code must acquire licenses from these companies.
  For information on licensing, see Appendix F in the standard.


Expired LZW patents
-------------------

Unisys owns patents on LZW compression, which is used by
Ppmtogif, and maybe on LZW decompression, which is used by Giftopnm.  IBM also
owns a patent that may cover the GIF tools.  Unisys offers a license of the
patent for trivial use for $5000.  Its U.S. patent (Number 4,558,302) expired
June 20, 2003.  In most of Europe, the patent expired June 18, 2004.  In
Japan, it was June 20, 2004 and in Canada, July 7, 2004.  IBM's U.S. patent
expired August 11, 2006.

Neither company has ever enforced the patent against trivial users of
it.  <http://news.cnet.com/news/0-1005-200-1713278.html> is an article
dated April 18, 2000 on the issue.
http://www.unisys.com/about__unisys/lzw/> is Unisys' view of the
matter.  For information from another perspective, see
<http://burnallgifs.org>.

The following Netpbm components may be restricted by these patents:
Ppmtogif, Giftopnm.

A good substitute for GIF if the patents are a problem is PNG (see
pngtopnm, pnmtopng), which was developed with a primary purpose of not
using any patented technology.

You can also use the -nolzw option on ppmtogif to avoid using the LZW
patent.  The images so generated are larger than traditional
LZW-compressed GIFs, but any GIF decoder can decode them just the
same.
