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RE: measuring contrast ratio and Windows Clear Type

From: Jan Eric Hellbusch <hellbusch@2bweb.de>
Date: Fri, 15 Aug 2014 20:16:34 +0200
To: "'Joe Chidzik'" <joe.chidzik@abilitynet.org.uk>, <w3c-wai-ig@w3.org>
Message-ID: <000c01cfb8b5$0c1d4570$2457d050$@2bweb.de>
Hi Joe and all,

maybe I should put my question a bit differently:

> I don't know if it's possible to detect (via CSS\JavaScript) if a user has
clear type
> enabled or not, but in my view, measuring the contrast via the values
provided in
> the CSS should be all that it is required to check adherence to the
success
> criteria.

I agree, because a web developer cannot make considerations for all screen
settings a user may have made.

In fact, the glossary in WCAG 2.0 basically says the same:

"Note 2: Because authors do not have control over user settings as to how
text is rendered (for example font smoothing or anti-aliasing), the contrast
ratio for text can be evaluated with anti-aliasing turned off."

But when reading the "understanding" documents for success criteria 1.4.3
and 1.4.6 I discovered a different approach:
http://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast7.html

"Note 1: When fonts have anti-aliasing applied to make them look smoother,
they can lose darkness or lightness. Thus, the actual contrast can be
reduced. Thicker stem widths will reduce this effect (thin fonts could have
the full stem lightened rather than just the ends). Using larger fonts and
testing for legibility in user agents with font smoothing turned on is
recommended."

Is that considered a reliable test? Antialiasing will deliver different
results on different user agents. 

Should antialiasing be turned on or off for measuring contrast ratios? ...
and for WCAG 2.0 conformance? 

BTW: Both suggestions appear on the same page, too (link above). 

Thanks 
Jan


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Jan Eric Hellbusch 
Tel.: +49 (231) 33005825 oder +49 (163) 3369925
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S
Received on Friday, 15 August 2014 18:16:49 UTC

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