Thread Subject: Flashing provisions
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From: Jared Smith
Date: Fri, Jul 20 2007 3:50 PM
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The General Requirements and the Web requirements state a Flashing
timing requirement (more than 3 per second) and then reference the
General Flash and Red Flash Thresholds which again specified the same
timing requirement. This is a bit confusing. I think these could
simply state, "Flashing must be under the General Flash and Red Flash
Thresholds" as these thresholds include the timing requirements.
The application of general and red thresholds within the definition is
also a bit awkward (to me). Here's a stab at clarifying and
simplifying the definition.
A sequence of flashes or rapidly changing sequences where all three of
the following occur:
1. There are more than three and less than 50 flashes within any
one-second period; and
2. The combined area of flashes occurring concurrently and
contiguously occupies more than a total of .006 steradians (25% of any
10 degree visual field on the screen); and
3. The relative luminance of the opposing changes is 10% or more and
the relative luminance of the darker image is below 0.80, or the
opposing changes are to or from a saturated red.
Note 1: A 10 degree visual field for standard screen sizes and viewing
distances is approximately a 341 x 256 pixel rectangle anywhere on a
1024 x 768 display.
Comments/questions:
- Removed the word "image" from the definition, recombined both timing
requirements, and recombined general and red requirements. This means
we could simply call this "Flash Threshold" for simplicity.
- Made some wording more consistent ("opposing changes",
"transitions", "flashes", etc.)
- What exactly is "a saturated red"? I'm assuming it is #ff0000 in
RGB, but if so, this certainly would have no different impact than
#ff0001. I also assume this is referring to my programmed colors, not
the colors as displayed on screen, correct?
- Shortened Note 1 and removed "For general Web content" as this
applies beyond the web.
Jared Smith
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