Re: A few issues with the proposed definition of contrast

On 3/9/07, Sean Hayes <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