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From: tgl@zog.cs.cmu.edu (Tom Lane)
Newsgroups: comp.fonts,comp.lang.postscript
Subject: Re: METAFONT & PostScript
Summary: Metafont does quite a lot that PS cannot.
Message-ID: <3455@pt.cs.cmu.edu>
Date: 31 Oct 88 01:05:18 GMT
References: <902@cps3xx.UUCP> <10417@s.ms.uky.edu> <422@trigraph.UUCP>
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In article <10417@s.ms.uky.edu> sean@ms.uky.edu (Sean Casey) writes:
>I'm no great fan of either, but I have to point out that METAFONT does a lot
>more to generate fonts of a certain size than Postscript does. You can always
>send font outlines to Postscript for scaling, but the results aren't going to
>look as good as if you let METAFONT do it.

To which john@trigraph.UUCP (John Chew) replies in article <422@trigraph.UUCP>:
>The criticism of PostScript is misleading.  Certainly if you create
>a pure bitmap or pure outline PostScript font, it will be scaled as
>a bitmap or an outline: poorly.
> 
>If however you design a proper algorithmic PostScript font (one 
>which makes rasterization decisions based on the current font size),
> then the result will be every bit as good as, and quite possibly
>identical to that of METAFONT.

I disagree.  Chew seems to believe that Metafont's only virtue is that it
allows for nonlinear scaling of font dimensions.  This is true, but is only
part of the story.  Metafont also uses extremely careful (= costly)
algorithms for digitization: i.e., deciding exactly which pixels to blacken
to represent the infinitely-precise character outline.  At low resolution
(meaning less than 1000dpi), good digitization makes a lot of difference in
the appearance of a character.  Metafont also allows the font designer to
specify character dimensions in pixel-dependent units, to assist in
selecting the best possible digitization.

While a PostScript printer with a very large font cache could perhaps afford
to use similarly expensive digitization algorithms, I doubt that any
currently available implementations do so.  In any case, a PostScript font
designer has no means of specifying resolution-dependent --- as opposed to
size-dependent --- adjustment of character outlines.  (Correct?  I thought
that PostScript carefully hides the printer resolution...)

While we are on the subject, it's not clear to me that PostScript truly
allows for nonlinear font scaling.  In particular, the AFM file format seems
to dictate linear scaling of all major character dimensions, including
x-height.  Hence there is not really much room for altering character shapes
depending on actual size.

I'm no expert on PostScript, so I'd welcome hearing contrary opinions.  For
one thing, how standard is AFM format?  For another, can you discover the
actual resolution of your device?

-- 
				tom lane
Internet: tgl@zog.bcs.cmu.edu
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