Thread Subject: Re: Flashing provisions
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From: Gregg Vanderheiden
Date: Fri, Jul 20 2007 10:10 PM
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I think what you are looking for might be in the notes. A specific screen
area is provided for standard content. The steradians is used because the
provision would apply to more than typical screens at typical viewing
angles. So people can use the measures provided or they can use their own
and justify it.
Gregg C Vanderheiden Ph.D.
> -----Original Message-----
> From: = EMAIL ADDRESS REMOVED =
> [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf
> Of Jared Smith
> Sent: Friday, July 20, 2007 6:39 PM
> To: TEITAC Web/Software Subcommittee
> Subject: Re: [teitac-websoftware] Flashing provisions
> Another issue...
> Unless I'm mistaken or misunderstanding something (I'm not an
> engineer), both steradians and "25% of any 10 degree visual
> field" are not testable. This is because they both change
> based on the viewing distance, something that we don't define
> or allow for. For instance, if I'm one inch from the screen,
> both .006 steradians and "25% of any 10 degree visual field"
> are VERY small.
> In order for either to be testable, we must either do
> something much different or we must define a typical or
> minimum viewing distance from which the 10 degree visual
> field must be measured. I'm not sure how we do that. If we
> can assume that viewing distance will always be relative to
> the display size (the bigger the display, the further I am
> likely to be from it), then we could do something like:
> "... 25% of any 10 degree visual field at a distance of 1.5
> times the greater of the display width or height."
> "1.5 times" assumes a typical minimum viewing distance that I
> just guessed at. This accounts for display size (anything
> from handheld devices to LCD projectors), visual field, AND
> the point from which that field is measured. This, of course,
> is very easy to test - for a two dimensional display that is
> roughly perpendicular to your line of sight it works out to
> always be a squared area that is 26% of the greater of width
> or height.
> Without some measure of viewing distance or some formula
> based upon display size, the flashing threshold will remain
> untestable as is.
> Of course, the other big problem is that even if we fix this,
> programmers and web designers still have little control over
> display size, so none of this is very useful to them anyways.
> OK, it's Friday and my brain is now officially fried - I'm out.
> Jared Smith
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