Re: [ft] Hinting and patents

[Adam Twardoch]

Ric,

the Apple hinting patents describe a hinting method using special 
outline-manipulating instructions that are included in the glyph 
descriptions inside of a TrueType font. The TrueType rasterizer 
interprets the hinting instructions contained in the font and distorts 
the outline according to these instructions for certain screen sizes so 
that certain pixels "snap" in and out of the outline. This way, by 
distorting the outline using the hinting instructions, the font 
developer controls the final appearance of the rasterized bitmaps.

While this particular hinting method is patented by Apple, there are 
other methods of hinting that can be used with outline-based fonts. In 
the UNPATENTED_HINTING mode, FreeType does not interpret the hinting 
instructions contained in the font but analyzes the outline shapes 
themselves.

Note that the patented Apple TrueType hinting gives very good screen 
results only for carefully hand-hinted fonts, and practically only in 
monochrome unantialiased mode. In the majority of scenarios these days, 
fonts are rendered using antialiasing (typically grayscale), and the 
majority of retail TrueType fonts are not hand-hinted but autohinted 
instead. For these fonts, alternative hinting methods such as FreeType’s 
UNPATENTED_HINTING method often will yield better results.

You could use an analogy: if the font is a website and the font 
rasterizer is a web browser, then the TrueType hinting instructions are 
the CSS stylesheets. In the patented Apple TrueType hinting mode, the 
web browser blindly renders whatever the CSS stylesheet is specifying. 
In FreeType’s UNPATENTED_HINTING method, the web browser discards the 
CSS stylesheet, interprets the contents the web page and displays it in 
a unified way that is optimized for the current reader. One could argue 
that a web page that has a very carefully designed, typographically 
balanced CSS stylesheets would suffer if the stylesheet is discarded and 
replaced by the web browser’s default. On the other hand, the user will 
not regret that many of the auto-generated, horribly designed CSS 
templates are discarded and a sensible browser treatment is applied 
instead.

As a side-note: current and future operating systems (Mac OS X, Windows 
XP, Windows Vista) rely less and less on the patented Apple TrueType 
hinting method. The Mac OS X font rasterizer and the ClearType 
rasterizer that is the alternate rasterizer in Windows XP and will be 
the default rasterizer in Windows Vista, ignore a large number of 
TrueType hinting instructions and only interpret some of them 
selectively. This has to do with the fact that as the physical screen 
resolutions are increasing and the antialiasing methods are being 
refined (including subpixel positioning), the "one set of instructions 
fits all" approach of the Apple TrueType hinting method makes less and 
less sense. Some modern rendering systems such as XcgfK 
(http://www.em2-solutions.com/news/xcgfk.htm ) completely ignore 
TrueType hinting instructions and rely exclusively on their own 
optimization methods.

Regards,
Adam Twardoch


Ric Flinn wrote:
> As I understand it, hinting is patented by Apple and
> many font venders pay royalties to use Apple's hinting
> techniques. In FreeType I see references to
> UNPATENTED_HINTING, but I'm not exactly sure what this
> means, or what the implications are if I define or
> undefine this build option.
>
> I'd like to better understand this issue, and I'd like
> to be sure that I'm not including any code that may
> cause patent issues in my finished products. I don't
> need to use hinting in my application, so removing
> hinting capability altogether is desired. I'm using
> FreeType 2.1.10.
>
> Ric Flinn
>