Proposal for SC 2.3.1

The following proposal is a revision to SC 2.3.1 and it's definitions for discussion on the 05 April 2007 teleconference.

2.3.1 Flash Threshold: Content does not flash more than 3 times in any one second period unless the flash is below the general flash threshold and the red flash threshold. How to meet 2.3.1

general flash threshold

A sequence of flashes or rapidly changing image sequences where all four of the following occur:

1. there are more than three flashes within any one-second period; and
2. the flashing is below 50 Hz; and
3. the brightness of the darker image is below .80 of full scale white brightness; and
4. the combined area of flashing occurring concurrently and contiguously occupies more than one quarter of any 10 degree visual field on the screen (or a total of .006 steradians).

Notes:

• For the general flash threshold, a flash is defined as a pair of opposing changes in brightness of 10% or more of full scale white brightness
• Brightness is calculated as 0.2126 * ((R / FS) ^ 2.2) + 0.7152 * ((G / FS) ^ 2.2) + 0.0722 * ((B / FS) ^ 2.2). R, G, and B are the red, green, and blue RGB values of the color; FS is the maximum possible full scale RGB value for R, G, and B (255 for eight bit color channels); and the "^" character is the exponentiation operator.
• An "opposing change" is an increase followed by a decrease, or a decrease followed by an increase.
• For general web content using a 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 x 768 pixels will provide a good estimate of a 10 degree visual field of standard screen sizes and viewing distances.
  
  

red flash threshold

transition to or from a saturated red where all three of the following occur:

1. there are more than three flashes within any one-second period; and
2. the flashing is below 50 Hz; and
3. the combined area of flashing occurring concurrently and contiguously occupies more than one quarter of any 10 degree visual field on the screen (or a total of .006 steradians).

Note: For general web content using a 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 x 768 pixels will provide a good estimate of a 10 degree visual field of standard screen sizes and viewing distances.