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More font hinting stuff

From: Raph Levien <raph@acm.org>
Date: Fri, 3 Dec 1999 15:08:17 -0800
Message-Id: <199912032308.PAA10698@adsl-63-196-208-218.dsl.snfc21.pacbell.net>
To: www-svg@w3.org
Hi svg'ers,

   I've been continuing to research font formats since my last screed,
largely in the context of design work for a new X extension for
advanced 2D graphics rendering. I thought I'd bring a heads-up to you
guys.

   First, there is a lot of variation in rendering for hinted type1
fonts. The Adobe renderer is a lot better than either of the two major
free implemntations, GhostScript and the one in the X server (which is
derived from donated IBM code). I was under the impression that the
free ones were better, so I was disappointed. Just a word of warning.
A comparison is available at:

      http://www.dcs.ed.ac.uk/home/jec/programs/xfsft/renderers.html

   Second, I came across a paper that explains how to do _awesome_
automatic hinted rendering. This is paper 89/2-17.ps in John Hobby's
bibliography (a rather impressive collection of documents, by the
way):

      http://cm.bell-labs.com/who/hobby/pubs.html

   This technology has some very interesting properties. First, it
doesn't depend on manual hints in the font; it works totally
automatically. This is significant because the current SVG font
proposal has no hints. Second, while the paper doesn't explicitly
discuss the issue, it would appear likely that it can be adapted well
to rotations and affine transformations. The constraint subsystem
already contains an "integer offset property" mechanism for getting
smooth, consistent results from diagonal lines. Third, it seems to be
very nicely script-independent. Type1's hinter contains a number of
features optimized for latinlike and kanji scripts.

   There is some interest within the free software community (Gnome
and X) in doing a production-quality implementation of these ideas. It
looks like they'll require quite a bit of investment of time and
mathematical skill. If there's anyone out there who'd be interested in
funding such an implementation, I'd be happy to hook you up.

   It would appear that the techniques in this paper are free of
patent problems. Certainly John Hobby is unaware of any such issues.

   Third, I've come across some patents relating to antialiased +
hinted fonts, ie using the hints to perturb the outlines, then filling
them using an antialiasing technique. Microsoft has a patent (US
5,684,510) that would appear to cover this, as does Apple (patent
number not handy right now, but I can dig it up).

   Thus, it seems like requiring antialiasing with hinting is probably
not a good idea. Since some people might like to use it if it were
available, it might be putting in an option, much like the existing
one for selecting antialiasing.

   Hope some of this information comes in handy.

Raph
Received on Friday, 3 December 1999 18:10:10 GMT

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