DjVuDigital is a very
efficient way of converting PostScript and PDF documents into DjVu. It relies
on a GhostScript driver named
GSDjVu that analyzes the sequence of rendering operations and
classifies each of them as foreground or background.
The rather sophisticated algorithm is fully described in this paper.
The resulting segmentation is then used to produce a DjVu file,
using, for instance, the DjVuLibre program csepdjvu.
This code was written five years ago
with the intention of making it freely available
to promote the development of DjVu.
Things did not happen as we wanted.
During the DjVu Summit
Conference, Carlos Domingo, new CEO of Lizardtech, agreed to the distribution of DjVuDigital
as a part of DjVuLibre. But AT&T Labs had to
release its part of the code, the GSDjVu Ghostscript driver. This took more
time than anyone expected.
Eventually, in June 2005, AT&T Labs released the
source code of the GSDjVu driver for Ghostscript under the terms of the Common Public License Version V1.0 (CPL).
We are very happy to finally see this code freely available,
and warmly thank all the persons who made this release happen.
The CPL is a genuine free software license that
unfortunately is incompatible with the GPL.
This is explained on the web pages of the Free
Software Fundation. This is very annoying because the GhostScript source
code is available under the terms of the GPL (also under
the AFPL which is too restricive for our purposes.)
The requirements of the CPL, including the
identified by the Free Software Fundation, only apply to the
redistribution of CPL licensed programs. Therefore we believe that
anyone is free to download both the GSDjVu and GhostScript source
code packages and to use them as they see fit. In particular,
anyone can combine and compile these source code
packages. However, we are certain that it is not possible
to redistribute the resulting
executable, because it is not possible to satisfy the redistribution
requirements of both the CPL and the GPL.
The above statement is merely the expression of our belief.
It should not be understood as a guarantee of any kind.
You must make your own opinion before compiling GSDjVu.
Do not use GSDjVu unless you understand the
consequences of this license incompatibility.
If you are determined to compile GSDjVu,
you will find much easier to use the
improved version prepared by the DjVuLibre
team (after all, we wrote this code in the first place.)
The updated source code is available from the DjVuLibre project page on Sourceforge. It comes with a
README file that explains how to compile a working
executable, and a COPYING file that discusses the
rather contradictory licensing conditions.
Because of the license incompatibility discussed above,
we cannot release precompiled binaries.
The original AT&T Labs release is available
| How to request a GPL release?|
The only practical way to solve the incompatibility issue is to
politely ask our AT&T friends to clarify their intentions.
Please send a brief email to
AT&T Intellectual Property Licensing
with a copy to
First thank them warmly because they worked very hard and
used their hard earned professional credit to help
release GSDjVu under a free license.
Second give your best argument to justify authorizing the
redistribution of GSDjVu under the GPL.
Here are a few examples:
Whatever the purposes of the GSDjVu open source release are,
this purpose would be better served by licensing terms that
facilitate the use of GSDjVu.
Legally, what does it mean to release a source code (GSDjVu),
whose operation technically depends on a second program (GhostScript),
under terms that are incompatible with those of this second program.
| Uses of GSDjVu besides DjVu|
In return we would like to drop a few ideas on commercialy feasible uses of
the GSDjVu technology besides DJVU compression. Do not hesitate to contact AT&T
<email@example.com> to commercially license GSDjVu for
GSDjVu is a very powerful technology that analyzes each page of an
electronically generated document and decomposes it as (1) a low
resolution continuous color background image, and (2) a collection of
high resolution foreground objects having each a single flat color.
Such a decomposition can be very useful:
PDF Optimization ---
The quality and size of PDF files vary
dramatically according to the quality of the input material.
The GSDjVu decomposition is a good basis to significatively
reduce the size of badly authored PDF files.
Most printers represent colors with dithering.
Large dithering patterns give accurate colors at the
expense of resolution. Small dithering patterns give
coarser colors with higher resolution. The GSDJVU decomposion
neatly identifies which parts of a page are best printed
using small or large dithering patterns.
Helping vision challenged persons ---
The GSDjVu decomposition
allows for dimming graphical embellishments that make reading
difficult and enhancing the contrast of the meaningful
text and graphics.