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From: roy@mchip00.med.nyu.edu (Roy Smith)
Newsgroups: alt.graphics,comp.graphics,alt.graphics.pixutils
Subject: Re: Why does Illustrator AutoTrace so poorly?
Date: 26 Apr 1993 13:05:57 GMT
Organization: New York University, School of Medicine
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Message-ID: <1rgmnl$cfr@calvin.NYU.EDU>
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mac@utkvx.bitnet (Richard J. McDougald) writes:
> Since there's no (not really) such thing as a decent raster to vector
> conversion program, this "tracing" technique is about it.  Simple stuff,
> like b&w logos, etc. do pretty well, while more complicated stuff goes
> haywire.

	The first and only thing I've ever tried to auto-trace was a piece
of a USCG nautical chart using Adobe Illustrator 3.2.  I wanted to get the
outline of the coast for Western Long Island Sound.  I was simultaneously
suprised at how good a job it did and disappointed at how poorly it did.  I
suspect what I gave it was a very difficult thing; not only is the coastline
very irregular, but overlaid on the chart are numerous sets of gridlines
(not only lattitude and longitude, but loran grids as well).  The most
common mistake it make was whenever the coastline was roughly parallel and
tangent to a grid line, it would take off following the gridline instead of
the coast.  I think the best improvement would be some sort of interactive
algorithm that would let you step in and say "no, dummy, you're going the
wrong way".

	Steve Reisberg, a friend of mine a few years back(*), did his
doctoral work analysing electron micrographs of filimentous phage (virii).
A good chunk of the work was writing a program to take a digitized
micrograph and automatically trace the centerline of the virus particles.
This is essentially the same problem that Illustrator tries to solve with
its auto-trace tool.

	In some respects the problem Steve worked on was harder, since he
was trying to do quantitative analysis of the virus structure and finding a
good centerline was only the first step, but a step on which all future
analysis depended.  However, in other respects, it was an easier problem
since the program could be written with a lot of knowledge about what the
virus particles were supposed to look like, and the analysis could be
restricted to those particles which happend to be relatively straight,
clean, and well imaged; you don't always have that freedom auto-tracing real
life images.  In any case, it gave me some insight into just how difficult
this problem is to solve in the general case.

	(*) Steve is no longer with us.  He and his wife disappeared while
on vacation in Hawaii a couple of years after they graduated.  Their last
known location was hiking in a densely wooded in a mountainous area.  While no
bodies were ever found, they are presumed to have been the victim of some
sort of fall or accident in the woods.
-- 
Roy Smith <roy@nyu.edu>
Hippocrates Project, Department of Microbiology, Coles 202
NYU School of Medicine, 550 First Avenue, New York, NY 10016
"This never happened to Bart Simpson."
