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The core of this program is derived from Martin Weber's
(martweb@gmx.net) Autotrace. Bryan Henderson adapted it to Netpbm in
February 2006.
Much of the Autotrace code has been rewritten to be easier to read and match
Netpbm coding style.
Pieces of Autotrace that duplicate other Netpbm programs or just don't fit
the Netpbm philosophy have been removed. In particular, Autotrace has the
ability to take formats other than Netpbm formats for input, to despeckle
the image before tracing, and to quantize colors before tracing. Pamtosvg
has none of that.
Pamtosvg uses libnetpbm to read the input image, process the command line,
manage memory, and do several other minor things. Autotrace has its own
code for those things.
Autotrace uses a shmaltzy trick to deal with open outlines. There is a
piece of the program that divides an outline at its corners and then creates
a curve for the pieces between every two corners. For an open outline,
there are segments of the outline at each end that are not between two
corners. One piece of code finds the corners, and another computes the
curves between them.
In order to use the closed outline code for the open outline case,
Autotrace includes a dummy corner at the start of the outline in the
list of corners. The curve-finding code then has a special case for
the segment after the last corner. Pamtosvg uses a cleaner approach.
The corner list is an actual list of corners -- there is no dummy
corner. The curve-finding code has two special cases for open
outlines -- one for the segment before the first corner, and one for
the segment after the last corner.
STRATEGY
--------
Autotrace is capable of many more vector graphics output formats
besides SVG. The basic curve tracing is the same for all; it just has
output formatting modules. Netpbm ought to be able to generate those
formats as well. SVG is just the beginning.
Of course, having a program that generates multiple output formats based
on command line options is not the Netpbm way to approach it. A pure
traditional Netpbm approach would be to have a converter between PAM
and each of the vector graphics formats.
That isn't practical because of the information that gets lost when you
convert from vector to raster form, and also because 99% of the logic
in converting between PAM and a vector graphics format is the same for
all the vector graphics formats.
Therefore, the strategy is to adopt a single vector graphics format
and use it as the common intermediate format. Right now, it looks
like SVG would be a good choice for that. However, it may turn out to
be better to create a vector graphics format specially for Netpbm.
The reason for that is that an intermediate Netpbm format has a rather
different requirement from all these other formats -- it isn't meant
to be transmitted or stored, but it is meant to be easy for a
programmer to work with.
We need a program to go the other way -- to convert from SVG to PAM.
I.e. a curve drawing program. The Ppmdraw program does this kind of
curve drawing (in fact, a Ppmdraw script can be considered a vector
graphics format). Ppmdraw itself might not be adaptable, but the
library routines it uses are probably all we need to convert SVG to
PAM.
The Pamtosvg code should be reworked to use a libnetpbm tuple array
instead of its at_bitmap_type for the raster.
Nobody has any plans to do any of this work. I document the strategy
only so that if someone decides to do some work, he can go in the
right direction.
COPYRIGHT CONSIDERATIONS
------------------------
Bryan took the code and has distributed it under a copyright license
granted to him, as a member of the public, by the authors. That
license is the GNU Lesser Public License Version 2.1. All the authors
offer that same license for Pamtosvg to the public. A copy of it is
in the Netpbm doc/ directory.
CREDITS
-------
Autotrace's source code listed the following as contributors to it:
Martin Weber <martweb@gmx.net>
Bernhard Herzog (Postscript, svg and sk export filter)
Ian MacPhedran (xfig export filter)
Martin Kroeker (bugfixes)
Tobias Polzin (bugfixes)
Kevin O'Gorman (Shockwave support)
MenTaLguY (png import filter)
Peter Cucka (bugfixes)
Enrico Persiani (emf export)
Johannes Schindelin (Magick import filter)
Masatake YAMATO (library, help with cvs)
Steffen Politzky (dxf export)
David A. Bartold (part of despeckle)
Han-Wen Nienhuys (rpm-spec file)
R. P. C. Rodgers (man page)
Allen Barnett (improved emf export)
Andrew Elia (dr2d export filter)
Ralf Stubner (bugfixes about pstoedit usage)
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