RE: [Devel] Type 1 rendering and Euler numbers

[Turner, David]

Hello Graham,

> -----Message d'origine-----
> 
> 2. Berthold Horn notes ('Hinting' of scalable outline fonts, 
> TUGboat, Volume 18 (1997), No. 4) that the less powerful hinting system 
> relies on a subtler rasterizer:
> 
> "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."
> 
> FreeType uses a single rasterizer for all font types, so 
> obviously cannot do this - I think. Any comments?
> 
That's right. The only thing you could do for the moment is modify the
Type 1 driver to automatically render a glyph bitmap when the load flags
contain the FT_LOAD_RENDER bit, and then use a different algorithm.

However, this would mean that later conversions of outlines, e.g. with 
FT_Glyph_To_Bitmap, would generate different results. I let you imagine
what kind of support nightmare this could be.

Making FreeType capable of using distinct rasterizers based on the original
font format would mean quite a number of changes to the library. Note that
this is uninteresting, but it's a lot of work.


> 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).
> 
Maybe yes. The Type 1 hinter now lags severely behind the automatic hinter
for certain fonts. For others, its results are still better (especially
for monochrome rendering).


Regards,

- David Turner
- The FreeType Project  (www.freetype.org)

> Best wishes,
> 
> Graham Asher
>