Thread Subject: FW: NEW PROPOSED LANGUAGE FOR 2.1-B and for EDITS TO THE DEFINITION

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From: Robert_Nerhood@Dell.com
Date: Fri, Jan 04 2008 10:40 AM

All,



Attached is the refined 2.1-B language and definition for discussion next week. Can this be placed in the version we will be discussing next week.



Thanks,



Rob



From: Gregg Vanderheiden [mailto: = EMAIL ADDRESS REMOVED = ]
Sent: Friday, January 04, 2008 11:17 AM
To: Thomas Albin; Nerhood, Robert
Cc: Gregg Vanderheiden
Subject: NEW PROPOSED LANGUAGE FOR 2.1-B and for EDITS TO THE DEFINITION





2.1-B - Flashing
Products must not flash more than 3 times in any one second period, unless:

* Flashing created by software or content meets provision 3-J Flashing
* For flashing created by hardware, the flashing element along with reflected flash from adjoining surfaces of the product is be below the general flash and red flash thresholds.

Rationale: This provides equivalent coverage for hardware. It does not cover extremely bright point sources that might cause flare within the eye as we could find no data at this time on which to base such a requirement.

=======================

(PROPOSED EDITS TO DEFINITION ARE SHOWN IN BOLD)



General Flash and Red Flash Thresholds

A sequence of flashes or rapidly changing image sequences where all three of the following are true:

1. There are more than 3 General Flashes and/or more than 3 Red Flashes within any one-second period; and
2. The flashing is below 50 Hz; and
3. The combined area of flashes occurring concurrently occupy an area of 0.006 steradians or more of any 10 degrees of visual field on the screen (25% of 10 degrees of visual field) at typical viewing distance,

where:

* a. For software and content: A General Flash is defined as a pair of opposing changes in relative luminance of 10% or more of the maximum relative luminance where the relative luminance of the darker image is below 0.80; and where "a pair of opposing changes" is an increase followed by a decrease, or a decrease followed by an increase, and
* b. For hardware: A General Flash is defined as a pair of opposing changes in luminance of 20 candellas/m2 and where "a pair of opposing changes" is an increase followed by a decrease, or a decrease followed by an increase, and
* c. A Red Flash is defined as any pair of opposing transitions involving a saturated red.

Exception: The flashing is a fine balanced alternating pattern such a white noise or a checkerboard-like pattern with "squares" smaller than 0.5 degree on a side (area less than .000125 steradians).

Note 1: For general software or Web content, using a 341×256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024×768 pixels will provide a good estimate of a 10 degree visual field for standard screen sizes and viewing distances (e.g. 15-17 inch screen at 22-26 inches). (Higher resolution displays showing the same rendering of the content yield smaller and safer images so it is lower resolutions that are used to define the thresholds.)

Note 2: A transition is the change in relative luminance (or relative luminance/color for red flashing) between adjacent peaks and valleys in a plot of relative luminance (or relative luminance/color for red flashing) measurement against time. A flash consists of two opposing transitions.

Note 3: For general software, or Web content,the current working definition in the field for "pair of opposing transitions involving a saturated red" is where, for either or both states involved in each transition, R/(R+ G + B) >= 0.8, and the change in the value of (R-G-B)x320 is > 20 (negative values of (R-G-B)x320 are set to zero) for both transitions. R, G, B values range from 0-1 as specified in "relative luminance" definition. (Harding and Binnie 2002)

Note 4: For general software, or Web content, tools are available that will carry out analysis from video screen capture.

Note 5: No tool is necessary to evaluate for this condition if flashing is less than or equal to 3 flashes in any one second or greater than 50Hz. Content automatically passes (see #1 and #2 above).

Note 6: 50Hz is used to coincide with the AC line frequency in Europe and other countries. However almost half of the photosensitive population is susceptible to 50Hz flashing whereas only 15% are susceptible to 60Hz. 75Hz or higher is recommended where possible.

Note 7: To fail, the threshold change in luminance (or relative luminance) must be true for all points within the .006 steradians. (It is not the average value.)


Gregg

------------------------

Gregg C Vanderheiden Ph.D.
Professor - Depts of Ind. Engr. & BioMed Engr.
Director - Trace R & D Center
University of Wisconsin-Madison
<http://trace.wisc.edu/ <http://trace.wisc.edu/> > FAX 608/262-8848

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