[Devel] Re: Type 1 rendering and Euler numbers

[Werner LEMBERG]

> I've had some trouble with the quality of Adobe Type 1 fonts at low
> resolutions (sample of cmr12.pfb at small ppem attached as a bitmap
> image enlarged threefold: note dropout on top-right branch of 'x',
> for example).

The Type 1 hinter in FreeType sucks.  There are some serious bugs, and
I will try to improve it in the near future.  However, these fixes are
rather related to the positioning of hints, not drop-out control.

> "Type 1 fonts use a different (undocumented) rasterization algorithm
> that first creates a continuous outline that has no drop-outs, but
> that is approximately 1/2 pixel too wide all the way around.  It
> then erodes this outline using Euler-number-preserving binary image
> operations – which cannot introduce drop-outs."

It's the first time I hear this.  Very interesting.  Any more
information?  Note that the rasterizer has set the dropout mode
hardwired to 2, regardless what the (TrueType) fonts asks for.  A
longer time ago I asked for the reason, but I got no answer.  You
might do some experiments and change it.

> 3. Would it help to turn on auto-hinting for Type 1 fonts? (Of
> course I'll try this myself, but any other experiences are welcome).

Currently the auto-hinter produces better results than the Type 1
hinter, I think.


    Werner