General flashing threshold
A sequence of flashes or rapidly changing image sequences where both the following occur:

  1. The combined area of flashes occurring concurrently (but not necessarily contiguously) occupies more than one quarter of any 335 × 268 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels and…

2. There are more than three flashes within any one-second period.

Note: For the general flashing threshold, a flash is defined as a pair of opposing changes in brightness of 10% or more of full scale white brightness, where brightness is calculated as .2126*R + .7152*G + .0722B using linearised R, G, and B values. Linearised-X = (X/FS)^2.2 where FS is full scale (usually 255 today).

An “opposing change” is an increase followed by a decrease, or a decrease followed by an increase.

Red flashing threshold
A transition to or from a saturated red where the following occurs: The combined area of flashes occurring concurrently occupies more than one quarter of any 335 × 268 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels and there are more than three flashes within any one-second period.

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