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Re: guideline 7.1 about screen flickering

From: David Woolley <david@djwhome.demon.co.uk>
Date: Wed, 25 Jul 2001 07:52:09 +0100 (BST)
Message-Id: <200107250652.f6P6q9302303@djwhome.demon.co.uk>
To: w3c-wai-ig@w3.org
Charles wrote:
> I am not so sure. The thing moves in my viewer at the sort of rate that is
> potentially a problem (between 5 and 50 hertz, roughly) for people with

The frame rate is 1/80ms, and there are four circuits in 30 frames,
so the complete sequence repeats at about 1.666 Hz, so I suspect it
may be too slow.

> photosensitive epilepsy, and is distracting for people with concentration
> difficulties. I think if it is going to be fine it will be so on the basis

However it is extremely distracting in the peripheral vision, so it
would fail on that point.

Incidentally, it's not technically accurate, as a real primary radar would
have a fast leading edge and a slow exponential trailing edge, whereas
this picture has slow leading and trailing edges.

> On Tue, 24 Jul 2001, Fitzgerald, Jimmie wrote:

>   really need to change their wording to 'element flicker' or something.  By
>   calling it screen flicker, I think monitor refresh rates.  And that is
>   something we as developers cannot control.

There is one case that I've seen a number of times where monitor refresh
rates are an issue and under designer control:  if you have a texture with
alternative scan lines light and dark, it will flicker at half the frame
rate, which is typically around 30Hz and very noticeable, if someone is
using an interlaced display.  I use an interlaced display at home because
my monitor, although about 10 years old, is still working quite adequately,
and that is the only way of getting the resolutin needed by modern software.
I'd consider it a waste of natural resources to commit it to land fill.
Received on Wednesday, 25 July 2001 02:52:17 UTC

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