Re: Anti-aliased font support library ready

[Jens Lautenbacher <jtl schlund de>]

Philip Armstrong <phil@kantaka.co.uk> writes:

> additional followup:
> 
> If you want to see why truetype antialiasing is awful, take a look at
> 
> http://www.kantaka.co.uk/freetype.png
> 
> and compare with
> 
> http://www.kantaka.co.uk/type1.png
> 
> The truetype was rendered with the freetype library, whilst the
> postscript font was rendered with t1lib.
> 
> There are several problems with the truetype font:
> 
> 1) The truetype standard says that letters *must* be aligned on pixel
> boundaries. This leads to the nasty 'jumps' in the apparent weight of
> the font as you increase the size. 

Nothing in freetype forces you to use HINTING (which is what you mean
with grid aligning.)

Freetype is capable of producing just AA glyphs without any hinting at
all, which, depending on the quality of the font (better: the hinting
in the font) will look better or worse.

Examples for perfect fonts are the ones from MS (arial, verdana, times
new roman, courier new..). Here for sizes between (if I remember
correctly) 9 and 16 point the hinted variant looks crisp clear.
 
> 2) The small pixel sizes look nothing like the larger ones.
> 
> By comparison the postscipt font, which is sub-pixel antialised looks
> *far* beter, and is readable down to the smallest point sizes ( if you
> can focus that small :) Of course, this also means that the font looks
> good on low-res devices like handhelds and tv screens. Psion and palm
> et al are missing a trick by not anti-aliasing their displays...)
> 
> There is at least one significant problem with the postscrit, which is
> that it appears to 'fade out' as you get to smaller point sizes. I
> think this is because t1lib is not using the hinting/scaffolding
> information contained in the font to 'fill in' the font at small point
> sizes.

As said above, you're missing the point. The hinting information for a
type1 font isn't as "strict" as it is for a truetype font. While a
conformant truetype hinting processor will give the exact same pixels
as any other conformant truetype hinting processor, this isn't true for
type1. At least the X11 type1 renderer has much space left for
improvement in using hinting. On the other hand, the hinting in almost
all free fonts be it type1 or truetype is very very bad, so it doesn't
get you anything most of the time.

But if hinting is good, it will improve drastically the readeability
of a font, and grid alignement helps very much with this.

For readability it is only a secondary goal to preserve e.g. the
interchar spacing. it is much more important to have vertical and
horizontal stems be sharp by not blurring them through AA.

        jtl