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slight edit to the definition of General Flash

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Tue, 11 Apr 2006 19:30:47 -0500
To: <w3c-wai-gl@w3.org>
Message-ID: <006701c65dc8$5ed1fbe0$eebddb46@NC6000BAK>
OOPs.  My error.   There is one clause missing from the definition of
general flash.   Just spaced it. 




The OFCOM guidance has the following condition (for the general flash only).

"This applies only when the screen luminance of the darker image is below
160 cd.m-2. "


When translated from TVs with 200 cd.m-2 max to the equivalent for Web
content this becomes:


This applies only when the brightness of the darker image is below .80 of
full scale white brightness. 


This should be placed in our definition at the end of note1 as shown below.
(sorry for missing this earlier)







general flash 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 341 x 256
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 1: 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, where 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. This
applies only when the brightness of the darker image is below .80 of full
scale white brightness.






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  
For a list of our list discussions  <http://trace.wisc.edu/lists/>

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Received on Wednesday, 12 April 2006 00:31:11 UTC

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