Re: [Devel]Oversampling and rounding TrueType glyphs

[Keith Packard]

> I have sent some notes regarding this very problem to the Render
> list. Did you receive it ? In all cases, please try the following
> method, and re-contact me if this doesn't work:

Somehow I missed it, sorry.  In any case, the scaling does indeed 
rasterize the glyphs correctly now, for example, here's an 'f' in
crude ascii graphics (8 intensity levels ' ','.',':',';','=','+','*','#'):

char 0x66 (f):
       :;==+**#########;            
      *#####;                       
########################            
      ######                        
      ######                        
      ######                        
      ######                        
      ######                        

You can see the edges of the glyph are nice and sharp.

A straightforward RGB decimation yields noticable chromatic aberrations,
the ClearType paper suggests a simple filter (they use a box) to reduce 
these effects; but filtering in this manner generates vertical edges which 
are no longer sharp.  The filter picks up samples across the sharp edge 
and smooths both the chromatic change along with the intensity change.  
Hmm.  That might be the key.

As a kludge, I changed the filter to confine itself within a pixel 
boundary; this ensures that sharp edges remain sharp, but generates 
additional chromatic effects.  The results can be compared here:

        http://xfree86.org/~keithp/render/clear.html

I'll have to ponder this a bit more.

address@hidden   XFree86 Core Team              SuSE, Inc.