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RE: 2.3 cleanup- URL reference?

From: Gregg Vanderheiden <po@trace.wisc.edu>
Date: Tue, 24 Feb 2004 11:09:39 -0600
To: 'Sailesh Panchang' <sailesh.panchang@deque.com>, w3c-wai-gl@w3.org
Message-id: <0HTL00J6UMC5E3@smtp4.doit.wisc.edu>
Hi Sailesh,

 

Sorry,  

 

This will all be 'connected' when it is finished.     I should have removed
the links from this when I posted it.  I just cut and pasted it from the
main doc so all the links broke.     Too tired I guess to catch it at 1:30
am.

 

We are still writing up the  Wisconsin Computer Equivalence Algorithm.  

 Document.   It is a bit complicated - and we are trying to write it as
clearly and simply as we can.

 

 

Apologies. 

 
Gregg

 -- ------------------------------ 
Gregg C Vanderheiden Ph.D. 
Professor - Ind. Engr. & BioMed Engr.
Director - Trace R & D Center 
University of Wisconsin-Madison 

  _____  

From: w3c-wai-gl-request@w3.org [mailto:w3c-wai-gl-request@w3.org] On Behalf
Of Sailesh Panchang
Sent: Tuesday, February 24, 2004 10:02 AM
To: Gregg Vanderheiden; w3c-wai-gl@w3.org
Subject: Re: 2.3 cleanup- URL reference?

 

I was trying to check out the Wisconsin Computer Equivalence Algorithm link
given in this mail. It gives a page not found error. The searchh on the
wisc.trace.edu site too was not fruitful. Will appreciate  if you can
correct the link address.

Thanks,

Sailesh

----- Original Message ----- 

From: Gregg Vanderheiden <mailto:po@trace.wisc.edu>  

To: w3c-wai-gl@w3.org 

Sent: Tuesday, February 24, 2004 1:19 AM

Subject: FW: 2.3 cleanup

 

Here is a cleaned up version of the new 2.3 proposal based on discussion on
the list and telecom.

 

Gregg

 

 

 


Guideline 2.3 Allow users to avoid content that could cause photosensitive
epileptic seizures.


Level 1 Success Criteria for Guideline 2.3


1.	Content that violates the General Flash Threshold or Red Flash
Threshold  is
<file:///C:\Documents%20and%20Settings\Caldwell\Local%20Settings\Temp\tmp003
2.html#markedpriordef#markedpriordef> marked in way that the user can access
prior to its appearance. [I] 


Level 2 Success Criteria for Guideline 2.3 


1.	Content does not violate the General Flash Threshold or Red Flash
Threshold. [V] 


Level 3 Success Criteria for Guideline 2.3 


1.	Content does not violate any Spatial Pattern Thresholds. [V] 

 

 

General Flash Threshold 

*	A sequence of flashes or rapidly changing image sequences is not
permitted when both the following occur: 

1.	the combined area of flashes occurring concurrently (but not
necessarily contiguously) occupies more than one quarter of any 355 x 268
pixel rectangle anywhere on the displayed screen area when the page is
viewed at 1024 by 768 pixels and 
2.	there are more than three flashes within any one-second period. 

For this general flash threshold - a flash is defined as a pair of opposing
changes in luminance (i.e., an increase in luminance followed by a decrease,
or a decrease followed by an increase) of 20 candelas per rectangle meter
(cd.m-2) or more and where the screen luminance of the darker image is below
160 cd.m-2. 

Red Flash Threshold 

*	A transition to or from a saturated red at any luminance level is
not permitted when both of the following occur: 

1.	the combined area of flashes occurring concurrently occupies more
than one quarter of any 355 x 268 pixel rectangle anywhere on the displayed
screen area when the page is viewed at 1024 by 768 pixels and 
2.	there are more than three flashes within any one-second period. 

For the red flash threshold - a flash is defined as any pair of opposing
transitions to or from a saturated red at any luminance level . (See notes 1
and 2) 

Spatial Pattern Thresholds 

*	Clearly discernible stripes consisting of more than five light-dark
pairs in any orientation are not permitted when the stripes are stationary
when the pattern occupies more than 40% of any 355 x 268 pixel rectangle
anywhere on the displayed screen area when the page is viewed at 1024 by 768
pixels. 
*	Clearly discernible stripes consisting of more than five light-dark
pairs in any orientation that change direction, oscillate, flash, or reverse
in contrast are not permitted when the pattern occupies more than 25% of any
355 x 268 pixel rectangle anywhere on the displayed screen area when the
page is viewed at 1024 by 768 pixels. 

Clearly discernable stripes are stripes where the screen luminance of the
darker bars in the pattern is below 160 cd.m-2 and differs from the lighter
bars by 20 cd.m-2 or more

Note: 

1.      Video waveform luminance is not a direct measure of display screen
brightness. Not all display devices have the same gamma characteristic, but
a display with a gamma of 2.2 may be assumed for the purpose of determining
electrical measurements made to check compliance with these guidelines.

2.      For the purpose of measurements made to check compliance with these
guidelines, pictures are assumed to be displayed with peak white corresponds
to a screen illumination of 200 cd.m-2. 

3.      Thresholds are based on ITC Guidance Note for Licensees on Flashing
Images and Regular Patterns in Television (Revised and re-issued July 2001)
(http://www.ofcom.org.uk/codes_guidelines/broadcasting/tv/vrs_code_notes/fls
h_imgs/?a=87101) 
as modified by the Wisconsin Computer Equivalence Algorithm.

Editorial Note: A free tool will be available from the University of
Wisconsin's Trace Center that will carry out the above analysis on Web
content.   The tool will be available by the second quarter of 2004. 

 

 

 


Definitions: 


 

Wisconsin Computer Equivalence Algorithm 

The Wisconsin Computer Equivalence Algorithm is a method for applying the
United Kingdom's ITC "ITC Guidance Note for Licensees on Flashing Images and
Regular Patterns in Television (Revised and re-issued July 2001)" to content
displayed on a computer screen, such as web pages and other computer
content. The ITC Guidance Document is based on the assumption that the
television screen occupies the central ten degrees of vision. This is not
accurate for a screen which is located in front of a person. The Wisconsin
Algorithm basically carries out the same analysis as the ITC Guidelines
except that is does it on every possible ten degree window for a
prototypical computer display. For complete details see http://__________.

Editorial Note:   Appropriate link to referen         ces will be provided
when they become available

marked in way that the user can access prior to its appearance 

            

The content is marked in a fashion that would allow the user to determine
that provocative material is coming so that the user may avoid it.   Some
methods that might be used for this include:

*         metadata on page

*         information in header (so search engine shows it)

*         notification on page before provocative information is
encountered.

Editorial Note: This definition needs work.

 

 
Received on Tuesday, 24 February 2004 12:09:48 UTC

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