Thread Subject: Re: New Flash Provision

Note

This archival content is maintained by WebAIM and NCDAE on behalf of TEITAC and the U.S. Access Board . Additional details on the updates to section 508 and section 255 can be found at the Access Board web site.

From: Phill Jenkins
Date: Sun, Apr 08 2007 10:10 PM

I don't think I understand this phrase:

b) the combined area of flashing occurring concurrently and contiguously
occupies less than one quarter of any 10 degrees of visual field.

nor is it defined. It is estimated by the following:

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.

So, can it not be simplified by just using a percentage? 341x256 is 11%
of 1024x768. (87,295/786,432)

And what if the user has the screen magnified and is right on the
"flashing content"? If its set to 8x , then 80% of the screen is flashing.
Is that the user's concern and not the author's? It seems to me that
this "10 degrees of visual field" is dependent on how close the users is
to the items flashing as well. For example, looking at a whole screen
1024 by 768 flashing, but from a distance of 10 meters is probably less
than 10 degrees. I believe that in any standard, more than one
stakeholders may have a role. Such as in the case when magnifying the
screen beyond its initial settings.

However, I do agree we should harmonize with new WCAG 2.0 wording.

btw, the rationale for this is because of "photosensitive seizure
disorders" which is broader than "photosensitive epilepsy" - but I do not
have a reference. Wikipedia redirects "seizure disorder" to Epilepsy.
[something I learned at CSUN 2007].

Regards,
Phill Jenkins
IBM Research - Human Ability & Accessibility Center
http://www.ibm.com/able





"Gregg Vanderheiden" < = EMAIL ADDRESS REMOVED = >
Sent by: = EMAIL ADDRESS REMOVED =
04/08/2007 07:18 PM
Please respond to
TEITAC General Interface Accessibility Subcommittee
< = EMAIL ADDRESS REMOVED = >


To
"'TEITAC General Interface Accessibility Subcommittee'"
< = EMAIL ADDRESS REMOVED = >
cc

Subject
[teitac-general] New Flash Provision






We should change the provision so that it is limited to those things that
are truly problem and so that it doesn?t cover flashing LEDs and other
things that are not a big problem.

We discussed this before. But didn?t have the latest WCAG wording. WCAG
has been working on this and their wording adopted last week is shown
below.

If we want to adapt this to 508/255 (where we must cover not only web
content but other flashing) it would look some thing like this.



<proposal for 508/255 wording>

No more than 3 flashes above thresholds
No part of the product flashes more that three times in any one
second period unless
a) the flashing is greater than 50 hz or
b) the combined area of flashing occurring concurrently
and contiguously occupies less than one quarter of any 10 degrees of
visual field
c) the flashing is not fully saturated red and the
change in brightness is less than 10 percent of full scale brightness.

<end proposal for 508 / 255>




WCAG proposal (for reference)


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

DEFINITIONS in WCAG 2.0
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.



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/> FAX 608/262-8848
DSS Player at http://tinyurl.com/dho6b

WebAIM is an initiative of:
Center for Persons with Disabilities (CPD) Utah State University