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Re: [ft-devel] Rendering artifacts

From: Werner LEMBERG
Subject: Re: [ft-devel] Rendering artifacts
Date: Mon, 26 Jul 2010 18:29:10 +0200 (CEST)

> That said i first noticed the invisibility problem while using
> seamonkey/firefox/whatever which all rely on fontconfig.

Hmm.  You should file a bug report for fontconfig.

> FWIW i tried using Liberation Serif under Vista and it does AA the
> glyphs, however the leg of k is perfectly visible.

Vista uses ClearType by default, not yet supported by FreeType (see

> And while at it, i'd like to point at another interesting case,
> namely Linux Biolinum where when using full native hinter and rgb AA
> the color fringing is just insane (again under Vista there's no
> fringing)

I suspect this is the same issue (this is, missing ClearType support).

> And a final remark, i'm using decent CRT monitor and in general do
> not use AA at all, it's just that a friend was preaching the
> ClearType to me for a while and i decided to try it out, and indeed
> i was pleasantly surprised (after trying different AA options here
> on linux and osx, i'd say that the thing doesn't look all that worse
> than bitmap/non-antialiased-but-well-hinted fonts)

ClearType consists of two components:

  (a) Rasterizing a font with a greatly enlarged horizontal
      resolution, using some nasty tricks (with help of a database of
      known `problematic' fonts) to make that work for old legacy
      fonts.  In particular, a bunch of instructions are disabled,
      mainly for handling diagonal strokes.  We don't have this in
      FreeType yet.

  (b) Using the result from (a) and applying a special (patented)
      filter to achieve a good color balance for subpixel rendering.

(a) gives improvements on a CRT also.


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