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RE: SC 2.2.2 (Blinking) and contrast ratio

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Mon, 17 Sep 2007 00:00:24 -0500
To: 'Christophe Strobbe' <christophe.strobbe@esat.kuleuven.be>, 'wcag' <w3c-wai-gl@w3.org>
Message-id: <02b601c7f8e7$a8deb550$146fa8c0@NC84301>
Blink and flash have now been redefined.    Does this address the concern?  



switch back and forth between two visual states in a way that that does not
qualify as flash <http://www.w3.org/WAI/GL/WCAG20/#flash-def>  (e.g. it is
too slow or the change in relative luminance is too small to qualify as

Note: The slower blink is in contrast with flashing
<http://www.w3.org/WAI/GL/WCAG20/#flash-def> , which refers to rapid changes
in brightness which can cause seizures. See general flash and
<http://www.w3.org/WAI/GL/WCAG20/#general-thresholddef>  red flash



a pair of opposing changes in relative luminance of 10% or more where the
relative luminance of the darker image is below 0.80

Note: Flash is characterized by rapid changes of relative luminance
occurring more than three times per second, while blink
<http://www.w3.org/WAI/GL/WCAG20/#blinksdef>  is less than three times per

Note: See general flash
<http://www.w3.org/WAI/GL/WCAG20/#general-thresholddef>  threshold and red
flash threshold for more precise information about the applicability and
constraints of flash.




 -- ------------------------------ 

Gregg C Vanderheiden Ph.D. 




> -----Original Message-----

> From: w3c-wai-gl-request@w3.org 

> [mailto:w3c-wai-gl-request@w3.org] On Behalf Of Christophe Strobbe

> Sent: Wednesday, September 12, 2007 4:57 AM

> To: wcag

> Subject: SC 2.2.2 (Blinking) and contrast ratio



> Hi,


> The following question came out of some work on the Unified 

> Web Evaluation Methodology (UWEM) [1].

> The May 2007 draft of WCAG 2.0 defines blink as "turn on and 

> off between 0.5 and 3 times per second", with a note saying: 

> "The slower blink is in contrast with flashing, which refers 

> to rapid changes in brightness which can cause seizures. See 

> general flash and red flash thresholds."


> However, the definition of blink does not specify a contrast 

> ratio between the on and of states, so any blinking fails the 

> success criterion, even if the contrast between the two 

> states is very low. 

> Of course, low contrast would fail SC 1.4.3 (Contrast 

> (Minimum)), but evaluators, especially automated tools, would 

> want to establish whether blinking content fails SC 2.2.2 by 

> itself, regardless whether it passes or fails SC 1.4.3.

> So, my question is: does *all* blinking content fail SC 

> 2.2.2? (I assume it currently does.) Should we add a note 

> about this to the definition of blink?


> Best regards,


> Christophe


> [1] <http://www.wabcluster.org/uwem1_1/> UWEM is based on 

> WCAG 1.0; checkpoint 7.2 covers blinking content.



> -- 

> Christophe Strobbe

> K.U.Leuven - Dept. of Electrical Engineering - SCD

> Research Group on Document Architectures

> Kasteelpark Arenberg 10 bus 2442

> B-3001 Leuven-Heverlee


> tel: +32 16 32 85 51

> http://www.docarch.be/ 



> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm



Received on Monday, 17 September 2007 05:00:39 UTC

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