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RE: SC 2.2.2 (Blinking) and contrast ratio

From: Christophe Strobbe <christophe.strobbe@esat.kuleuven.be>
Date: Mon, 17 Sep 2007 10:44:55 +0200
Message-Id: <6.2.5.6.2.20070917104121.03b0aad0@esat.kuleuven.be>
To: w3c-wai-gl@w3.org

Hi Gregg,

At 07:00 17/09/2007, you wrote:
>Blink and flash have now been redefined. Does this address the concern?
>
>
>
>blink
>
>
>
>switch back and forth between two visual states in a way that that 
>does not qualify as 
><http://www.w3.org/WAI/GL/WCAG20/#flash-def>flash (e.g. it is too 
>slow or the change in relative luminance is too small to qualify as flashing)
>
>Note: The slower blink is in contrast with 
><http://www.w3.org/WAI/GL/WCAG20/#flash-def>flashing, which refers 
>to rapid changes in brightness which can cause seizures. See 
><http://www.w3.org/WAI/GL/WCAG20/#general-thresholddef>general flash 
>and red flash thresholds.

Yes, thanks, that addresses my concern.

Best regards,

Christophe

>
>
>
>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 
><http://www.w3.org/WAI/GL/WCAG20/#blinksdef>blink is less than three 
>times per second.
>
>Note: See 
><http://www.w3.org/WAI/GL/WCAG20/#general-thresholddef>general flash 
>threshold and red flash threshold for more precise information about 
>the applicability and constraints of flash.
>
>
>Gregg
>  -- ------------------------------
>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
BELGIUM
tel: +32 16 32 85 51
http://www.docarch.be/ 


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Received on Monday, 17 September 2007 08:45:17 GMT

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