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Re: Request for Review: Working Draft of WCAG 2.0

From: Matthew Wickline <aware-colorlab@hwg.org>
Date: Fri, 13 Aug 2004 05:27:43 -0700
Message-ID: <411CB3BF.3070901@hwg.org>
To: public-comments-wcag20@w3.org

 > codifying color contrast
:
 > Any ideas are appreciated


When I read that text, the first thing I thought of was finding the
effective luminance of the two colors and requiring some minimum
separation. Then I compare that to

      http://www.w3.org/TR/AERT#test-color-contrast

and find that this is exactly where you're at currently. Once a
minimum separation value was determined, it'd be trivial to provide
a tool allowing web designers to input two colors and find out of
they satisfy the requirement. However, finding the value is the hard
part.

I don't personally have (or know of) any data that would suggest a
certain value, or make finding the value a simple matter of looking
in some table. I may be mistaken, but it sounds like an empirical
question. :/

If I were one of those usability gurus, I'd probably round up a
nice-sized sample of users of various ages and visual accuity and
have them perform tasks on web pages of various colors (maybe using
a variety of monitors as well... some lcd, some crt). The tasks
might be things like clicking some specific linked text in a minimal
amount of time or reading content and answering comprehension questions.

Hopefully this data would give some sort of contrast difference
requirement to ensure that x% of viewers will be able to access the
content without suffering losses in seek time or comprehension. A
statistician would probably need to help out with the sample
selection and results analysis to ensure that the values are
statistically valid (at a high confidence level) with a sufficiently
small margin of error.

For higher % values, you would need lower contrast difference. The
WG could select some % value (maybe 95 or 99) and then find the
associated contrast differential value.

Yeah, that's a bunch of work. Maybe somone like these guys could be
talked into taking it on:

      http://psychology.wichita.edu/surl/usability_news.html

I'm afraid I can't think of any way to get a good number without
actually testing though :/

-matt

(that guy from
     http://colorfilter.wickline.org/
     http://colorlab.wickline.org/
)
Received on Saturday, 14 August 2004 03:56:59 UTC

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