Re: [ft] Algorithm Of Freetype

[Werner LEMBERG]

Hello Zéyǔ!


> Background
>
> On the tradition screen,one pixel have R/G/B three sub pixel.  Some
> algorithm like Microsoft ClearType. (Here some paper like displaced
> filtering for patterned display it calculate the minimum perceptual
> color error.)  I think these algorithm designed for "font display".
> Here my job is to research the panel sub pixel arrangement and sub
> pixel rendering for oled screen.  As we all know, Samsung have the
> Pentile arrangment in RGBG which one pixel have only two sub pixel.

Hehe, I hear this Samsung stuff the first time, so I'm not one of the
`all' :-)

> Question:
>
> 1. what does mac or apple system using for "font display".  Is that
>    the “truetype”?

`TrueType' is a font technology using second-order Bézier curves.  It
is not related to font display at all.  A similar font using
third-order Bézier curves is CFF (from Adobe).  Both formats are used
in OpenType fonts (which today usually have the file extension
`.otf').

> 2. ClearType using 3 channel to calculate the rendering font.  [...]

My knowledge regarding this filtering stuff is very limited;
hopefully others can answer this.

> 3. Because the ClearType only do the horizontal so some Vertical
>    Shape may have sawtooth?  There are many reason:
>
>    1. horizontal have three subpixel;
>    2. human visual system are sensitive to the horzontal direction.

I suggest that you read the following, very detailed work on TrueType
hinting (and in particular ClearType)

  http://www.beatstamm.com/Typography/index.htm

                                 *  *  *

The main question, however, is whether you need to take care of
sub-pixel arrangement at all for fonts!  Given that OLED screens have
200dpi and higher, normal font rendering should be sufficient, no?  It
would be great if you can give us more information here.


    Werner