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Re: Clarification of duration of flashing or flickering (Success Criteria 2.3.1)

From: <Accessys@smart.net>
Date: Wed, 28 Oct 2009 07:54:55 -0500 (EST)
cc: w3c-wai-ig@w3.org, public-comments-wcag20@w3.org
Message-ID: <Pine.LNX.4.58.0910280751130.7691@fzneg.arg>

remember that most of these "standards" are usually a 90th percentile  so of
100 affected people 10 might still not be helped....
  you propably would not be violating the WCAG but you might still
cause a problem in a very small percentage of the people who might be
observing this.

Bob



On Tue, 27 Oct 2009, Phill Jenkins wrote:

> Is the duration of the flashing or flickering (i.e., more than one second
> of time) a factor in determining accessibility compliance to WCAG 2.0
>         See Success Criteria 2.3.1 http://www.w3.org/TR/WCAG20/#seizure
>         "... do not contain anything that flashes more than three times in
> any one second period..."
>
> In my special case example, there is a slightly less than 1 second
> duration of 3 flashes in an Adobe Flash image at the top of a draft
> Shanghai EXPO 2010 page.
>
> WARNING - currently it flashes 3 times for slightly less than one second,
> then repeats several seconds later.
>         see http://fr.expo2010.cn/indextest.htm
>
> Assuming the developer adds a capability to stop the repeating Adobe Flash
> movie, is it still a problem because it flashes 3 times, regardless of the
> duration (e.g., 1 second, 10 seconds, etc.)?  Or does it need to flash
> more that 3 times a second of time for more that 1 second of duration?
>
> The "Understanding Guidelines 2.3" further mentions: "likely to cause
> seizure when viewed even for a second or two."
>         see http://www.w3.org/TR/UNDERSTANDING-WCAG20/seizure.html
>
> metrics to consider: Frequency, Duration, and Size (the text only really
> address frequency and size, not duration)
>         frequency:      (or interval) more than 3 flashes per second of
> time? (3 to 50 Hz)
>         duration:       more than one second duration of time? if it
> flashes more than 3, but for less than 1 second, is it a problem?
>         size:           341 x 256 pixel block or larger - see
> http://www.w3.org/TR/WCAG20/#general-thresholddef
>
> Since my example only flashes 3 times and not more than 3, and it soon may
> change to not repeat - Guidelines 2.3 says "more than three", then I think
> I do not have a problem, but I'm not sure - hence the question to the
> list.  Your informed opinions welcomed.
>
> I also believe the text and explanation can be simplified.  For example:
> 1. by addressing the three different metrics; frequency, duration, and
> size.
> 2. by addressing the lower and upper limits of each.  For example, if the
> frequency is 40 times in a second, but only lasts 1 second or less,
> regardless of size it may be hardly noticeable and not be a problem.
> 3. add some more common passing and failing examples.  The two existing
> ones are good.
>
> Regards,
> Phill Jenkins,
>

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Received on Wednesday, 28 October 2009 12:55:22 GMT

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