Re: [Devel] Rendering (by FreeType) and hinting of Latin small 'a'

[David Turner]

Hello Vadim,

Vadim Plessky wrote:
> I'd like to discuss (again) rendering of Serif fonts, and, in particular (to 
> narrow the scope) - Latin small 'a'.
> I have prepared a web page with examples demonstrating different rendering of 
> this glyph
> http://freetype.newmail.ru/misc/hinting-a.html
>
> [...]
>
> Now about problem I see at a moment.
> 1) topology of 'a' is destroyed at all examples, except non-AA rendering.
> I refer here to central, near-horizontal curve, in the middle of 'a'
> enabling sub-pixel rgb decimation doesn't help here.
I have introduced some changes in the automatic and Postscript hinters
lately to deal with disappearing curved diagonals (like in "S" or "2").
There are chances that these might also enhance the hinting of
your "a"s. Could you test the rendering of the current CVS code
to see if something changed ??

> 2) in ftview rendering, even bottom part of 'a' is disconnected from the 
> vertical stem.
> It's very visible at screenshot in natural size, and on enlarged s/s as well.
This is not very surprising, since the second glyph doesn't have any
hint on the lower stem. The Postscript hinter relies on what is provided
by the font file and won't try to detect stems on its own.

Note that the auto-hinter does render all three glyphs identically, since
their outlines are the same.



> 3) My testing of 5 different Times clones (variants), in addition to the 
> version I develop,  demonstrates, that all variants of Times, with exception
>  of Times New Roman, have similiar problem described above.
> See screenshots at th ebottom of th epage (Times New Roman is 2nd in series, 
> each three rendered glyphs are 12pt, 11pt, 10pt Latin 'a')
>
> Here are my questions:
> a) can this *topology* (visually broken  curve) issue be fixed?
> I demonstrated problem on example of 'a', but many other glyphs are affected 
> (in AA or RGN-AA modes), too.
Maybe, please test and report your opinion on that..


> b) how rendering (by FreeType, not too much interested in Adobe Type Manager 
> or Windpows' rasterizer) of middle part of 'a' can be enhanced?
> Should I artificially deformate curve to make constrains snapping to 
> horizontal position? (like is done in Times New Roman)
> This is not very desirable, as 'a' in Times New Roman has too small bottom 
> part, IMO, and this is not easy for screen reading.
> Diagonal hinting also doesn't help here, as, frankly speaking, this part 
> does't conform to diagonal hinting definition.
Try to make the stem slightly larger when it connects to the vertical
stem in the "a". This should help make it stronger/visible. Otherwise,
I don't see what could really done..


> c) Is it possible, in some way, to increase *tension* for FT rasterizer when 
> it follows some part of the contour/curve?
> It's like of driving a car with high speed, and follow smooth turn to, say, 
> left at 80km/hour.
> It can be done, if you increase your speed instantly /with acceleration/ :-)
> So, I think we should find a way to do the same with such curves.
> Is it possible to do?  What are your opinions?
I fail to understand precisely what you mean here. Do you have anything
more visual as an explanation (maybe a small graphics could help ??)


Best Regards,

- David