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Re: Colour Contrast and Text Shadows

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Thu, 03 Nov 2011 17:25:01 +0100
To: James Nurthen <james.nurthen@oracle.com>
Cc: WCAG <w3c-wai-gl@w3.org>
Message-id: <6DEF9BEF-07ED-4D35-A286-B74EE93F9FFB@trace.wisc.edu>
Yes if done correctly, it can be used to create the contrast needed. I'm not sure if "shadow" is quite the right word since shadows only would provide contrast for two sides of the character.  Halo might be a better description.   A black outline on a letter has also been used. 

the "readable white text" example is a good example of adding a dark outline to a letter to make it have better contrast. 

However the shadows on the first items (text shadows -- and - fuzzy text shadows)   on the page you indicate actually seems to reduce contrast -- and may cause the letters to fail if the otherwise would have succeeded.  in order to help with contrast they 'shadow' would have to be at the opposite end of the lightness scale - not the same as the letter. 

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
and the Global Public Inclusive Infrastructure Project
http://Raisingthefloor.org   ---   http://GPII.net

On Nov 3, 2011, at 5:02 PM, James Nurthen wrote:

> I was posed an interesting question the other day about the use of text shadows to overcome colour contrast issues
> This is similar to the "Readable White Text" example at http://www.w3.org/Style/Examples/007/text-shadow.en.html
> Can someone use a text shadow in order to meet the colour contrast requirement? It seems like they should be able to - as the example on the page above seems very readable, but I'm not sure how I would go about determining the luminosity contrast ratio of the above example as the ratio is different at different parts of the letter.
> A similar - but related - question has also been posed to me about text over css gradients. Were the background colour is a gradient (or a pattern) which point do we use in order to determine the luminosity contrast ratio?
> Regards,
> James
Received on Thursday, 3 November 2011 16:25:57 UTC

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