GIF PATENT CONTROVERSY

Ploticus does not read GIF files. Ploticus writes run-length-encoded (RLE) GIF files. Our understanding is that these RLE GIF files do not use patented LZW compression.

Ploticus uses the miGIF package to produce RLE GIF output. miGIF includes this statement:

Copyright (C) 1998 Hutchison Avenue Software Corporation
               http://www.hasc.com
               info@hasc.com

Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted, provided
that the above copyright notice appear in all copies and that both that
copyright notice and this permission notice appear in supporting
documentation.  This software is provided "AS IS." The Hutchison Avenue
Software Corporation disclaims all warranties, either express or implied,
including but not limited to implied warranties of merchantability and
fitness for a particular purpose, with respect to this code and accompanying
documentation.

The miGIF compression routines do not, strictly speaking, generate files
conforming to the GIF spec, since the image data is not LZW-compressed
(this is the point: in order to avoid transgression of the Unisys patent
on the LZW algorithm.)  However, miGIF generates data streams that any
reasonably sane LZW decompresser will decompress to what we want.

miGIF compression uses run length encoding. It compresses horizontal runs
of pixels of the same color. This type of compression gives good results
on images with many runs, for example images with lines, text and solid
shapes on a solid-colored background. It gives little or no compression
on images with few runs, for example digital or scanned photos.

                              der Mouse
                     mouse@rodents.montreal.qc.ca
           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B

                            ivo@hasc.com

FUTURE OF GIF

At the current time the future of GIFs is clouded by the fact that the LZW patent holder requires licenses for software that creates LZW GIFs.

In response there is currently an industry movement away from GIF, in favor of PNG, which has superior compression and no red tape. The only disadvantage with PNG is that old browsers do not support it, and as time goes by, this problem will diminish.

Because of all this, PNG support has been added to ploticus as of version 1.2, and GIF support, even though it is non-LZW, may be discontinued at some point in the future.