Thread Subject: Re: Flashing provisions
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From: Jared Smith
Date: Fri, Jul 20 2007 5:40 PM
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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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