- 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>
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