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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>
</div>
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<div id="cleartype-patents">
<h2>The ClearType Color Filtering Patents Have Expired!</h2>
<p>Since August 2019, all patents related to ClearType color
filtering have expired worldwide.</p>
<p>The affected patents were</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 covered 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>
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<div class="updated">
<p>Last update: 17-Aug-2020</p>
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