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Re: A few issues with the proposed definition of contrast

From: Christophe Strobbe <christophe.strobbe@esat.kuleuven.be>
Date: Mon, 12 Mar 2007 12:47:20 +0100
Message-Id: <>
To: w3c-wai-gl@w3.org

At 03:01 11/03/2007, Loretta Guarino Reid wrote:
>GV: The background would be what is immediately surrounding the 
>letter in the author defined presentation.   It the user scales the 
>font or changes the background etc, then the author is not 
>responsible under this guideline.
>Sean: HTML and similar technologies are too fluid to consider there 
>being a single "author defined presentation", there are many things 
>that cause text to move wrt. its background, scrolling, resizing the 
>viewport etc. - is the author relieved from responsibility when 
>these happen? I'd guess you'd say not, but then it outlaws any 
>scrolling container with a border.
>I don't understand your argument about scrolling. Is it that 
>scrolling doesn't guarantee any visual break between the scrolled 
>content and the border? In general, scrolling doesn''t change the 
>background and foreground colors.

Imagine that you have assigned different colours to paragraphs and to 
heading levels (h1 red, h2 blue, etc), and that you have a background 
image that does not scroll (CSS: background-attachment: fixed). When 
the user scrolls the text, different colours will move over the 
background image, resulting in different levels of contrast.
I'm not sure if this is what Sean had in mind.

I assume you would need to find the lowest contrast level that could 
occur in this situation, and that this contrast determines pass or fail.

Best regards,


Christophe Strobbe
K.U.Leuven - Departement of Electrical Engineering - Research Group 
on Document Architectures
Kasteelpark Arenberg 10 - 3001 Leuven-Heverlee - BELGIUM
tel: +32 16 32 85 51

Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
Received on Monday, 12 March 2007 11:47:42 UTC

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