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Re: [ft] Regression in rendering quality with subpixel antialiasing

From: David Turner
Subject: Re: [ft] Regression in rendering quality with subpixel antialiasing
Date: Wed, 20 Sep 2006 14:46:01 +0200

Hello Bernd,

thank you for providing me with the additionnal screenshot, they were
exactly what I needed (the ones provided with the bug-report weren't
enough informative). 

The short answer to your question is that, to get rid of the bluriness,
you should select a different hinting mode (medium or strong/full in
your font preferences dialog), which is rather easy.

To get the exact *exact* same results than before, you will also have to
re-enable the patent-infringing bytecode interpreter, if your build of 
FreeType didn't do that.

However, I consider doing the latter  to be a rather bad thing, or even in
the case of Debian, a grave political mistake since I believe it goes completely
against the goals of Debian; And I never quite understood why the FreeType deb
package always had the bytecode enabled by default in this distribution (or in
Ubuntu); the first thing I do when I install one of them is to re-install a 
build of FreeType.

I'll let the political discussion for later, and will now try to explain the
"problem" with more details, for those who want to understand the issue

- your fonts.conf shows that you've selected the "light" hinting mode
  (called "hintslight" in fontconfig parlance), which normally corresponds
  to the least possible distorsion in order to respect the original glyph
  outlines. The consequence of this is also fuzzier rendering, à la Mac OS X

- however, the "before" screenshot also show that you used a build of 2.1.10
  with the patent-infringing bytecode interpreter *enabled*. In this specific
  case, 2.1.10 and previous versions simply ignore the hinting mode you
  provided and always rendered the glyphs with the bytecode interpreter

  which I considered a bit stupid, since this denies any user preferences.

- in 2.2.1, the font engine was slightly modified, first to improve the
  "light" hinting mode results, but also to force FreeType to not use the
  bytecode interpreter if this mode was selected.

  this, in order to enable users of the bytecode-enabled FreeType (like
  unsuspecting Debian and Ubuntu users :-) to get "light" hinted text
  as well *if* they choose to (the "light" mode isn't a default on any
  distribution I know). This was done completely on purpose, and is
  a feature, not a bug :-)

So the real problem is that you've selected the "light" hinting mode, while
not knowing what it meant. Which isn't surprising since it probably didn't
change anything to your text rendering when you were on 2.1.10

No, another note about the "after" screenshot: if you're on a LCD, you'll 
see that they exhibit annoying color edges. This is a bug in the filtering
code used by libXft and Cairo. More on this later.

- David Turner
- The FreeType Project  (

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