User's Manual

English

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 soft-

ware. (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 les. To avoid entanglement with

the Unisys LZW patent, GIF reading support has been removed altogether, and the GIF writer has

been simplied to produce “uncompressed GIFs”. This technique does not use the LZW algorithm; the

resulting GIF les are larger than usual, but are readable by all standard GIF decoders.

“The Graphics Interchange Format(c) is the Copyright property of

CompuServe Incorporated. GIF(sm) is a Service Mark property of

CompuServe Incorporated.”

Appendix C – PNG decoder

Header part:

/* png.h - header le for PNG reference library

* libpng 1.0.2 - June 14, 1998

* For conditions of distribution and use, see the COPYRIGHT NOTICE below.

* COPYRIGHT NOTICE:

* The PNG Reference Library is supplied “AS IS”. The Contributing Authors

* and Group 42, Inc. disclaim all warranties, expressed or implied,

* including, without limitation, the warranties of merchantability and of

* tness for any purpose. The Contributing Authors and Group 42, Inc.

* assume no liability for direct, indirect, incidental, special, exemplary,

* or consequential damages, which may result from the use of the PNG

* Reference Library, even if advised of the possibility of such damage.

* Permission is hereby granted to use, copy, modify, and distribute this

* source code, or portions hereof, for any purpose, without fee, subject

* to the following restrictions:

* 1. The origin of this source code must not be misrepresented.

* 2. Altered versions must be plainly marked as such and must not be

* misrepresented as being the original source.

* 3. This Copyright notice may not be removed or altered from any source or

* altered source distribution.

* The Contributing Authors and Group 42, Inc. specically permit, without

* fee, and encourage the use of this source code as a component to

* supporting the PNG le format in commercial products. If you use this

* source code in a product, acknowledgment is not required but would be

* appreciated.