W3C home > Mailing lists > Public > public-pfwg@w3.org > February 2015

Action-1571 re CSS Composite and Contrast Calculation

From: Janina Sajka <janina@rednote.net>
Date: Tue, 17 Feb 2015 09:24:54 -0500
To: W3C WAI Protocols & Formats <public-pfwg@w3.org>
Cc: Gregg Vanderheiden <gv@trace.wisc.edu>
Message-ID: <20150217142454.GD1287@opera.rednote.net>
During our discussion of issues and concerns arising from CSS Composite
during our regular weekly teleconference on 28 January last:
http://www.w3.org/2015/01/28-pf-public-minutes.html#item06

I was actioned to request information from Dr. Gregg Vanderheiden
concerning the history behind WCAG 2.0's 4.5 ratio:
https://www.w3.org/WAI/PF/Group/track/actions/1571

His response follows below.

Dr. Gregg Vanderheiden writes:
> it was Trace working with Aries Arditi the Lighthouse for the blind.
> 
> 
> The current tools work for evaluating text and background at any point in time. 
> 
> We had graded backgrounds at the time=  and text that ran over multiple background colors.  
> 
> As for dynamic — you can calculate the effective background at any point in time.     
> 
> The trick is to change the lightness/darkness of the text as it moves over the backgrounds.    
> 
> You can’t solve  text over a mesh - but that is hard to read by all.
> 
> 
> 4.5 was chosen rather than 5 because at a contrast ration of 5:1 you can’t have to different things contrast with a third.  you can only have two.  But at 4.5 there is just enough room to have  “A” contrasts with “B” which contrasts with “C” .    But A has to be essentially black, and C needs to be essentially white  ( very slight tint of white). 
> 
> We even have color charts that show the colors you can use.
> 
> So how can I help you.   
> 
> gregg
> --------------------------------------------------------
> Gregg Vanderheiden Ph.D.
> Director Trace R&D Center
> Professor Industrial & Systems Engineering
> and Biomedical Engineering University of Wisconsin-Madison
> Co-Director, Raising the Floor - International - http://Raisingthefloor.org <http://raisingthefloor.org/>
> and the Global Public Inclusive Infrastructure Project -  http://GPII.net <http://gpii.net/>
> > On Feb 11, 2015, at 5:38 PM, Janina Sajka <janina@rednote.net> wrote:
> > 
> > A question to you from the WAI PF Working Group who's been digging into
> > our group memory recently ...
> > 
> > We've  been looking at visual contrast concerns in recent CSS draft
> > specifications. We're coalescing around the view that we may need some
> > new WCAG techniques, and probably some automated tools to properly
> > support authors who want to do the right thing by contrast.
> > 
> > Among other things, we see today's technologies using multiple layers
> > (more than just foreground/background), transparencies and gradients
> > that make human contrast calculations difficult, though we do believe
> > tools could be developed that could work.
> > 
> > As we discuss this we're recalling that you had someone do some research
> > back in the days when WCAG developed the 4.5 contrast ratio, but we're
> > not recalling who that was. Can you help identify that person for us?
> > 
> > Thanks in advance for any wisdom you can share on this.
> > 
> > Janina
> > 
> > 
> > -- 
> > 
> > Janina Sajka,	Phone:	+1.443.300.2200
> > 			sip:janina@asterisk.rednote.net
> > 		Email:	janina@rednote.net
> > 
> > Linux Foundation Fellow
> > Executive Chair, Accessibility Workgroup:	http://a11y.org
> > 
> > The World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI)
> > Chair,	Protocols & Formats	http://www.w3.org/wai/pf
> > 	Indie UI			http://www.w3.org/WAI/IndieUI/
> > 
> 

-- 

Janina Sajka,	Phone:	+1.443.300.2200
			sip:janina@asterisk.rednote.net
		Email:	janina@rednote.net

Linux Foundation Fellow
Executive Chair, Accessibility Workgroup:	http://a11y.org

The World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI)
Chair,	Protocols & Formats	http://www.w3.org/wai/pf
	Indie UI			http://www.w3.org/WAI/IndieUI/
Received on Tuesday, 17 February 2015 14:25:18 UTC

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