Path: utzoo!mnetor!uunet!husc6!necntc!ima!trb
From: trb@ima.ISC.COM (Andrew Tannenbaum)
Newsgroups: comp.fonts
Subject: Re: Universal font standard
Message-ID: <952@ima.ISC.COM>
Date: 13 Apr 88 20:18:14 GMT
References: <3178@gryphon.CTS.COM> <219@ateng.UUCP> <7645@brl-smoke.ARPA> <701@sun.soe.clarkson.edu>
Reply-To: trb@ima.UUCP (Andrew Tannenbaum)
Organization: Interactive Systems, Boston, MA
Lines: 54

In article <701@sun.soe.clarkson.edu> nelson@sun.soe.clarkson.edu.UUCP (Russ Nelson) writes:
> Doug is right.  Isomorphic fonts look nice iff you have enough bits to
> represent them, which implies that low-resolution fonts should be represented
> using bitmaps, while high-resolution fonts should be represented using
> outlines.

As Dr Peter Karow points out in "Digital Formats for Typefaces"
URW Verlag 1987 ISBN 3-926515-01-5 (this is the English Version)

	(p. 106)
	Inherent in the hierarchy, and fundamental in the URW
	philosophy, is that the IK format has a digital precision which
	is greater than that required by the typesetting machine.
	Letters in IK format are stored in a raster of 15,000 x 15,000
	per em.  This has the advantage that when preparing coarser
	rasters there is no interference between the stored raster and
	the target raster.

He goes on to explain that at 400 rasters/em, which he considers the
current average for good typesetting machines, the samples would be
every 37.5 lines, which is sufficient, whereas if you were sampling
from an 800 rasters/em master, there would be major problems in
generating a smooth image at both 400 and 401 rasters/em (for
instance).

That takes care of the problem of reducing the incidence of aliasing
problems in scaling - a finely grained master coupled with other
smoothing strategies will get you your best scaled bitmap typefaces.

For commonly used coarse grain typefaces, like typical screen
typefaces, you are going to get more palatable results by hand tuning
anyway.  My point is that I don't think that isomorphism is the real
problem, I think that if you take any typeface and scale it down to 100
rasters/inch (current screen size, approximately), it's going to look
ugly without tuning.

The notion of 15000 raster/em masters might make you uncomfortable, but
your system isn't going to be continually referring to the master.
I just don't think that you can just dismiss isomorphic typefaces.

I am talking about the case where you are generating typeface families,
not the case where you have a Postscript engine and you want to
generate a 11 point Times Roman on a 87 degree slant on on a 13 degree
baseline on a 300 dots/inch grid on the fly.  I don't think anyone is
going to give you beautiful typefaces yet in real-time with those kind
of constraints, though Adobe does a hell of a job.  Karow does discuss
other formats besides bitmap, he covers various vector formats and
greyscale formats.

While I don't worship Dr. Karow as the one true master, I would
definitely recommend his book.  If anyone can suggest a better
reference for digital typeface formats, let me know.

	Andrew Tannenbaum   Interactive   Boston, MA   +1 617 247 1155