Steve Martin wrote:
> 
> > Hmn, would it be useful or feasible to allow POV to read .zip files
> > directly? Are there any license restrictions on .zip compression, or any
> > other reason this wouldn't be done?
> 
> I don't know if there are any license restrictions on the zip format
> (which, I believe, was invented by PKWare in their PKZip product).
> However, if PKZip (and the zip file format) uses LZW compression,
> there is indeed a huge legal stink going on. Unisys is claiming that
> anyone who uses, creates, downloads, or otherwise even thinks about
> any software that reads, writes, translates, or otherwise processes
> practically anything that even touches LZW needs a written license
> from them. Their Web site includes in this blanket statement such things
> as the PDF file format used by Adobe Acrobat, Postscript-2, the
> V.42bis modem technology, and others. If one were to add the ability
> to read LZW-compressed material into POV-Ray, the way the Unisys site
> reads, the authors of the code, the users of the resultant program,
> and anyone who downloaded an image created with the code would be
> liable for patent infringement litigation.
> 
> Read all about it at http://www.unisys.com/unisys/lzw
> 
> (BTW, according to the GNU Web site, this whole stink is why GNU
> zip was created, to get around legal entanglements with the
> compress program, which uses LZW. This is also why their site
> boasts of using no GIF files, as GIF files use LZW compression.)

POV-Ray already uses LZW (support for GIF's as heightfields).  I'm not
sure we have a written agreement with Unisys, since that feature
predates my joining the team.  I'll ask.  If it becomes a serious
problem, we also support PNG heightfields.

POV-Ray also uses (as part of PNG support) zlib, which includes
functions that provide support for GNU zipped files.  The gzip manual
page says that gzip and PKZip both use Lempel-Ziv rather than LZW, so
that should be completely clear of problems.

That handles feasibility.  So, how useful do people think such a thing
would be?

-Mark Gordon

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