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Re: [ft] Hinting and patents

From: Adam Twardoch
Subject: Re: [ft] Hinting and patents
Date: Fri, 30 Jun 2006 22:32:24 +0200
User-agent: Thunderbird (Macintosh/20060516)


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 ( ) completely ignore TrueType hinting instructions and rely exclusively on their own optimization methods.

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

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