W3C home > Mailing lists > Public > w3c-wai-er-ig@w3.org > June 2002

Re: Automatically testing Web content for flicker

From: Terje Bless <link@pobox.com>
Date: Sun, 9 Jun 2002 14:38:49 +0200
To: Phill Jenkins <pjenkins@us.ibm.com>
cc: w3c-wai-er-ig@w3.org
Message-ID: <r01050300-1015-F3CFC7107BA511D6B38E00039300CF5C@[]>

Phill Jenkins <pjenkins@us.ibm.com> wrote:

>I meant that it is an issue to have this unnecessary checkpoint in WCAG.
>My point, and I think Nick's, was that it should not be in WCAG, and we
>should not be trying to find methods to test to add to the WCAG success
>criteria because it is not a content responsibility.  Flicker is handled
>by the display's __mhz and the browser - so there is no requirement on
>the author.

Hmmm. I'm not sure I agree. If I understand correctly, photosensitive
epilepsy is triggered by specific frequencies of flicker that can be
generated by an animated GIF or a Flash file[0], or possibly even dynamic
content altered via a javascript. Achieveing a flicker rate of between 5
and 60 Hz (which is what the website suggest as the most dangerous range)
should be possible even accidentally. Making sure your content does not
contain any such seems emminently suitable for the WCAG, if perhaps a bit

But I may be mistaken?

Whether it makes sense to attempt to _test_ for this is a different matter.

[0] - Based on the fact that certain video games and tv programmes that
      for one reason or another (showing strobe lights, say) cause the
      screen to flicker in certain patterns are claimed to induce
      epileptic attacks.

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Received on Sunday, 9 June 2002 10:32:55 UTC

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