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RE: A few issues with the proposed definition of contrast

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Mon, 12 Mar 2007 12:01:10 +0000
To: Loretta Guarino Reid <lorettaguarino@google.com>
CC: Gregg Vanderheiden <gv@trace.wisc.edu>, WCAG-WG <w3c-wai-gl@w3.org>
Message-ID: <7261AC2A5F73904CA41773C8F00813FF1C670D50@EA-EXMSG-C309.europe.corp.microsoft.com>
LGR: Sean, I don't understand how the issues that you raise wouldn't also apply to a more functional approach. They seems to relate to whether the author has sufficient knowledge or control of possible layouts to determine the background for text.

SH: The potential benefit of a more functional approach is that it addresses the legibility of the content as whole, as opposed to specifically limiting to worst case pointwise pixel comparisons. Of course similar issues apply that in some circumstances the content may be rendered in ways which are illegible, but if there exist typical content configurations in which text can be viewed in a manner which is legible, then in my opinion it should pass.


Sean Hayes
Standards and Policy Team
Accessible Technology Group
Microsoft
Phone:
  mob +44 7977 455002
  office +44 117 9719730



________________________________
From: Loretta Guarino Reid [mailto:lorettaguarino@google.com]
Sent: 11 March 2007 02:02
To: Sean Hayes
Cc: Gregg Vanderheiden; WCAG-WG
Subject: Re: A few issues with the proposed definition of contrast



On 3/9/07, Sean Hayes <Sean.Hayes@microsoft.com<mailto:Sean.Hayes@microsoft.com>> wrote:
GV: First, many of these comments don't have to do with the proposal per se.  They are generic questions about background that would apply to any contrast measurement I believe.   Would you agree?

Sean: Yes, I'd have to agree, contrast is notoriously difficult to measure. When you try to come up with a general method which is going to work across all web technologies I think you are on a losing wicket. Which is why previously I have tried to argue for a more functional approach based on whether the content could be used by individuals who have been assesed under clinical conditions to have atypical sight. Not that the content has to necessarily be tested by such individuals (although clearly that is the best approach), but that (with high inter-rater opinion) it could be.

Sean, I don't understand how the issues that you raise wouldn't also apply to a more functional approach. They seems to relate to whether the author has sufficient knowledge or control of possible layouts to determine the background for text.

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.

GV: Yes all this is true.  The author should not have a background image moving about behind the text that would not be different enough from the text to have the required contrast.

Sean: I'm more worried about the text moving about in front of the background. If you have to take worst case scenario's this is going to be almost impossible to meet in even fairly pedestrian and perfectly accessible content.

How is the text moving in front of the background?  Is this scrolling and reflow? Or is there a different scenario?

GV: If you do not specify the font or background color then you automatically pass.
Sean: But you are specifying the colors - you are just using symbolic names. You have to use these symbols correctly. It has been pointed out that CSS3 deprecates system colors, but its been in CR since 2003. It also allows opacity in all colours, which completely screws your formula.

How is the author specifying the colors in this situation?

...



Sorry to be a pain about this, as I do believe that high contrast modes are valuable to end users and we need to find a way to ensure they are available; I just don't believe we will come up with a single defensible test that we can write down which will actually be effective.

I think we may end up with a test that is conservative for some complex layouts and technologies. I think that would still be helpful.

Sean Hayes
Standards and Policy Team
Accessible Technology Group
Microsoft
Phone:
  mob +44 7977 455002
  office +44 117 9719730

Loretta
Received on Monday, 12 March 2007 12:01:24 GMT

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