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<h1><a href="index.html">FreeType</a> & Patents</h1>
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<div id="bytecode-patents">
<h2>The TrueType Bytecode Patents Have Expired!</h2>
<p>Since May 2010, all patents related to bytecode hinting
have expired worldwide. It it thus no longer necessary to
disable the bytecode interpreter, and starting with
FreeType version 2.4, it is enabled by default.</p>
<p>The affected patents were</p>
<div class="quote">
<p><a href="https://patents.google.com/patent/US5155805">
Patent US5155805:<br>
<em>Method and apparatus for moving control points
in displaying digital typeface on raster output
devices</em></a></p>
<p><a href="https://patents.google.com/patent/US5159668">
Patent US5159668:<br>
<em>Method and apparatus for manipulating outlines
in improving digital typeface on raster output
devices</em></a></p>
<p><a href="https://patents.google.com/patent/US5325479">
Patent US5325479:<br>
<em>Method and apparatus for moving control points
in displaying digital typeface on raster output
devices</em></a></p>
</div>
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<!-- ************************************************** -->
<div id="other-patents">
<h2>ClearType Color Filtering Patent Issues</h2>
<p>A survey from June 2007 shows no less than ten patents
from Microsoft that cover ClearType.</p>
<div class="quote">
<p><a href="https://patents.google.com/patent/US6219025">
Patent US6219025:<br>
<em>Mapping image data samples to pixel sub-components
on a striped display device</em></a></p>
<p><a href="https://patents.google.com/patent/US6225973">
Patent US6225973:<br>
<em>Mapping samples of foreground/background color
image data to pixel sub-components</em></a></p>
<p><a href="https://patents.google.com/patent/US6239783">
Patent US6239783:<br>
<em>Weighted mapping of image data samples to pixel
sub-components on a display device</em></a></p>
<p><a href="https://patents.google.com/patent/US6243070">
Patent US6243070:<br>
<em>Method and apparatus for detecting and reducing
color artifacts in images</em></a></p>
<p><a href="https://patents.google.com/patent/US6282327">
Patent US6282327:<br>
<em>Maintaining advance widths of existing characters
that have been resolution enhanced </em></a></p>
<p><a href="https://patents.google.com/patent/US6307566">
Patent US6307566:<br>
<em>Methods and apparatus for performing image
rendering and rasterization operations</em></a></p>
<p><a href="https://patents.google.com/patent/US6393145">
Patent US6393145:<br>
<em>Methods apparatus and data structures for
enhancing the resolution of images to be rendered on
patterned display devices </em></a></p>
<p><a href="https://patents.google.com/patent/US6421054">
Patent US6421054:<br>
<em>Methods and apparatus for performing grid fitting
and hinting operations</em></a></p>
<p><a href="https://patents.google.com/patent/US6624828">
Patent US6624828:<br>
<em>Method and apparatus for improving the quality of
displayed images through the use of user reference
information </em></a></p>
<p><a href="https://patents.google.com/patent/US6973210">
Patent US6973210:<br>
<em>Filtering image data to obtain samples mapped to
pixel sub-components of a display device</em></a></p>
</div>
<p>Essentially, these patents cover several different
things, which can be grossly sub-divided into</p>
<ul>
<li>the process of displaying images where data is
‘mapped’ to individual (e.g., LCD)
sub-pixels, instead of whole pixels,</li>
<li>the process of displaying said images after filtering
them for various purposes, e.g., reducing color fringes,
and</li>
<li>the process of dealing with metrics and spacing
rounding in a sub-pixel world.</li>
</ul>
<p>It is possible that Microsoft acquired other patents
related to the field in the previous years.</p>
<p>Please note that above claims do <em>not</em> cover the
enhanced interpretation of TrueType bytecode
instructions as discussed
in <a href="https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx">Greg
Hitchcock's whitepaper</a>.</p>
</div>
<h3>Patent Claims, Prior Art, and Validity</h3>
<p>Steve Gibson claims that
the <a href="https://www.grc.com/ctwho.htm">technique used by
ClearType is a reinvention of a 20-years old thing used on
the Apple II</a>. His exact words are</p>
<div class="quote">
<p>Thus, Microsoft's ‘ClearType’ application of
sub-pixel text rendering does not represent the dramatic
breakthrough that they claim and <em>it can not be the
valid subject for intellectual property
acquisition</em>.</p>
</div>
<p>(emphasis added).</p>
<p>Unfortunately, we believe that Mr. Gibson doesn't
understand patent law well. Under the current US regime,
any minor improvement to a previous technique can be
considered an ‘invention’ and
‘protected’ by a patent under the right
circumstances (e.g., if it is not totally trivial). If we
look at
the <a href="https://www.google.com/patents/US6219025">first
ClearType related patent mentioned above</a>, we see that
the <a href="https://www.google.com/patents/US4136359">Apple II
Wozniak patent</a> covering this machine's display technique
is listed <em>first</em> in the patents' citations. This
shows that both Microsoft and the patent examiner who
granted the patents were aware of this ‘prior
art’.</p>
<p>We are not trying to defend Microsoft here, just wanting to
avoid feeding false hopes to people who would like to see
the patent revoked.</p>
<p>Another popular view is
that <a href="https://answers.google.com/answers/threadview?id=723683">these
patents are too general to be enforceable</a>. Well, to be
fair, some of the claims in these patents do indeed use
rather vague descriptive terms (even for a patent lawyer or
an ‘expert in the field’). This is
absolutely <em>not</em> surprising, it is a direct
consequence of how the patent game works.</p>
<p>We won't cover this in greater detail since there
are <a href="https://www.iusmentis.com/patents/claims/">many</a>
<a href="https://www.tms.org/pubs/journals/JOM/matters/matters-9007.html">interesting</a>
<a href="https://en.wikipedia.org/wiki/Claim_(patent)#Basic_types_and_categories">pages</a>
on the subject. However, in case you invalidate a single
patent claim (e.g., with prior art), that doesn't mean the
whole patent is busted. Any other independent <em>and</em>
dependent claim can still be enforced.</p>
<p>Some of these patents have up to 40 claims. Invalidating
them is going to need <em>serious</em> prior-art, even if
there are also strong chances to invalidate the most general
claims in there. For example, many of the cheap LCD screens
on digital cameras have used a screen where each pixel is
either red, green, or blue, with colour images directly mapped
to them; they have been doing it for years, even when
displaying text or menus, and this corresponds exactly to what
the most general claims cover. If we can find a proof that
the technique was deployed before the patent's filing date, we
could have valid prior art to bust these.</p>
<h3>Possible Work-Arounds</h3>
<p>People have proposed alternatives to the ClearType color
filtering method. A very good example is
the <a href="http://www.oyhus.no/SubLCD.html">SubLCD</a>
technique, which employs a different way to use sub-pixels
compared to Microsoft's ClearType implementation. Its
author even says it doesn't infringe the ClearType
patents.</p>
<p>Unfortunately, the FreeType team doesn't share this
enthusiasm. The reason is precisely the very vague patent
claims described previously. There is a non-negligible
(even if small) chance that these claims also cover the
SubLCD technique. The situation would probably be different
if we could invalidate the broader patent claims, but this
is not the case currently.</p>
<h3>Does FreeType Implement Any of the Patented Techniques?</h3>
<p>Technically, no. The patents cover the whole process of
generating and displaying sub-pixel images. Since the font
engine doesn't do the display part, it cannot infringe.
Apart from that, FreeType has provided the capability of
converting vector shapes into un-filtered sub-pixel images
for a long time.</p>
<p>By default, FreeType's scan-line converter returns
‘gray’ sub-pixel images, where for each pixel
the color components are equal (this is, R=G=B). The result
is visually identical to gray anti-aliasing and cannot
infringe any of the ClearType patents.</p>
<p>Similarly, the LCD-specific filtering API is disabled by
default, which means that it returns an error and doesn't
alter sub-pixel images.</p>
<p>You can override these limitations by activating option
<code>FT_CONFIG_OPTION_SUBPIXEL_RENDERING</code> in
FreeType's <code>ftoption.h</code> configuration file, but
you should do that at your own risk.</p>
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<p>Last update: 13-Feb-2018</p>
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