Re: [Devel] Dropouts in AA text

[David Turner]

Hi Keith,

> 
> This makes sense except that smaller sizes have the diagonal present so at
> least in the raw form, the diagonal edges are not coincident.  It must be
> the TrueType hints which are causing the problem.  The output at smaller
> sizes looks as if no hinting was done.
> 
It _is_ the hinting that creates the problem. The glyph programs were
written a long time ago now, and didn't foresee the use of high-quality
anti-aliasing..

> > There is no generic way of solving the problem of "incorrectly" hinted
> > glyphs. We could try to provide drop-out control in the anti-aliasing
> > renderer, but this would require significant work. Another solution is
> > to use a monochrome renderer to generate 4x times bigger glyph _with_
> > drop out control, then filter them down..
> 
> Even the monochrome rasterizer won't completely solve the problem; I
> suspect the diagonal would be one pixel wide at the oversampled resolution
> and then nearly disappear when resampled.
>
Actually, it really depends on the filter you're using. The one used in
Windows (and in FT 1.0) only uses 5 gray levels and produces 'reasonable'
diagonals for this kind of glyphs.. Of course, the curves are somewhat less
smooths with most glyphs..

> I guess I should go buy better fonts.
> 
Or try to improve significantly the auto-hinter, which I'll start
in January, hopefully :-)

- David