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RE: A few issues with the proposed definition of contrast

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Thu, 15 Mar 2007 23:10:41 +0000
To: Gregg Vanderheiden <gv@trace.wisc.edu>, 'Christophe Strobbe' <christophe.strobbe@esat.kuleuven.be>, "w3c-wai-gl@w3.org" <w3c-wai-gl@w3.org>
Message-ID: <7261AC2A5F73904CA41773C8F00813FF1C6D99FB@EA-EXMSG-C309.europe.corp.microsoft.com>

I've been in contact with some colour experts at Microsoft, regarding the colour space issue, and their suggestion is to use two formulas - one for sRGB and a second one based on CIE L*; which is the lightness channel of a more general colour space, and one which most other colour models are based on.

L* has the added advantage of being more perceptual based, as well as being more widely applicable. I have asked them to create an equivalent formulation and we should have it in a week or so.
- Sean.

-----Original Message-----
From: w3c-wai-gl-request@w3.org [mailto:w3c-wai-gl-request@w3.org] On Behalf Of Gregg Vanderheiden
Sent: 12 March 2007 14:31
To: 'Christophe Strobbe'; w3c-wai-gl@w3.org
Subject: RE: A few issues with the proposed definition of contrast

- one method is to make sure that the worst case passes  (Standard

Another is to not do that

Another is to make sure that it doesn't fail unless the user does something
- -and that they could move the text back off the fail area to read it if
they need to (and they know they can since they put it there).

 -- ------------------------------
Gregg C Vanderheiden Ph.D.

> -----Original Message-----
> From: w3c-wai-gl-request@w3.org
> [mailto:w3c-wai-gl-request@w3.org] On Behalf Of Christophe Strobbe
> Sent: Monday, March 12, 2007 6:47 AM
> To: w3c-wai-gl@w3.org
> Subject: Re: A few issues with the proposed definition of contrast
> 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
> --
> 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
> http://www.docarch.be/
> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
Received on Thursday, 15 March 2007 23:10:54 UTC

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