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RE: CLOSED: Issue #344

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Tue, 13 Dec 2005 11:04:03 -0600
To: <w3c-wai-gl@w3.org>
Message-ID: <002b01c60007$3921df10$8c17a8c0@NC6000BAK>

Hi Chris 

You are correct. I believe their comments have to do with the old formula. 

The current algorithm was developed to be color deficiency tolerant.   As
you point out - no algorithm will give the same contrast for all users for
all color combinations.   The slides we posted give some idea for color
performance though they do not (and really cannot from what I understand)
simulate all the types of colorblindness.

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

-----Original Message-----
From: w3c-wai-gl-request@w3.org [mailto:w3c-wai-gl-request@w3.org] On Behalf
Of Chris Ridpath
Sent: Tuesday, December 13, 2005 10:52 AM
To: Roberto Scano (IWA/HWG); w3c-wai-gl@w3.org
Subject: Re: CLOSED: Issue #344

> Here is it:
> http://english.contrastocolori.org/
Thanks! However, I'm not sure how to interpret that formula. Looks like I'll

have to wait for the formal paper in a couple of months.

The article raised a couple of contentious issues that should be addressed 
before the group settles on a final algorithm.

"The W3C algorithm isn't intended for color blindness." This referred to the

previous algorithm but I think it applies to the current algorithm as well. 
Our bug 1736: "Current algorithm in 1.4.1 and 1.4.3 takes color deficiency 
into account  by using luminosity contrast." was closed but I still have 
some concerns. For example the color red (#ff0000) on a black (#000000) 
background has a contrast ratio of 1:5.25 which means it's OK for someone 
with good color perception. A person with protanopia would perceive the red 
as much darker and the contrast ratio would be much lower and not OK for 

"No single algorithm alone, used ahead of time to define a set of colors, 
can later adapt itself to different environmental conditions." Yes, there 
needs to be some sort of disclaimer on whatever algorithm we settle on that 
it's not perfect. Your mileage may vary depending on environmental 

Received on Tuesday, 13 December 2005 17:04:21 UTC

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