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contrast algorithm for 1.4.3: Contrast (Minimum)

From: Christophe Strobbe (on behalf of BenToWeb) <christophe.strobbe@esat.kuleuven.be>
Date: Fri, 01 Feb 2008 21:09:22 +0100
Message-Id: <6.2.5.6.2.20080201205832.02d1c500@esat.kuleuven.be>
To: public-comments-wcag20@w3.org

Hi,

Success criterion 1.4.3 relies on an algorithm 
for relative luminance [1] that is different from 
the algorithm in the draft for “Techniques For 
Accessibility Evaluation And Repair Tools” [2]. 
Research in BenToWeb investigated four different 
formulas for calculating colour contrast:

* WAI Accessibility Evaluation and Repair Tools 
(Ridpath and Chisholm, 2000), brightness equations (“AERT/B”),

* WAI Accessibility Evaluation and Repair Tools 
(Ridpath and Chisholm, 2000), colour contrast equations (“AERT/CC”),

* W. S. Thune (2003) [3] has provided a series of 
equations, known as the Catman equations, using 
linear, quadratic and cubic functions (Catman1, Catman2, Catman3),

* WCAG 2.0 – Working Draft 17 May 2007: contrast ratio definition (WCAG2).

AERT/B turned out to be closer to real user 
experience (based on user testing) than the other 
algorithms. User testing led to the 
recommendation of a brightness difference of at least 66.8.

[1] http://www.w3.org/TR/WCAG20/#contrast-ratiodef

[2] http://www.w3.org/TR/AERT#color-contrast

[3] http://www.iastate.edu/~class.12003.engl.313/cps/contrast.html


Best regards,

Christophe Strobbe



-- 
Christophe Strobbe
K.U.Leuven - Dept. of Electrical Engineering - SCD
Research Group on Document Architectures
Kasteelpark Arenberg 10 bus 2442
B-3001 Leuven-Heverlee
BELGIUM
tel: +32 16 32 85 51
http://www.docarch.be/ 


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Received on Friday, 1 February 2008 20:15:15 GMT

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