Thread Subject: Re: Contrast

From: Smith, Jamie
Date: Wed, May 09 2007 12:10 PM

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Gregg,
please send link of tool!

-----Original Message-----
From: = EMAIL ADDRESS REMOVED =
[mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of Gregg
Vanderheiden
Sent: Wednesday, May 09, 2007 1:32 PM
To: 'TEITAC Web/Software Subcommittee'
Subject: Re: [teitac-websoftware] Contrast

Hi Andrew,

I think that this is defined sufficiently that you COULD have automatic
testing - but it would have to be a very complicated and incredibly
intelligent tool (for some content) that could figure out the exact
outlines
of the characters and compare them to the surrounding color. But with
aliased text over a multicolor or dithered background I would love to
see the algorithm used to separate the two on a pixel level.

So we have to rely on human testing for some types of content and
background. As Sean pointed out - the equations make it clear what is
sufficient contrast. But you may need a human to determine what is
text
and what is background in order to apply them.


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



> -----Original Message-----
> From: = EMAIL ADDRESS REMOVED =
> [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of Sean
> Hayes
> Sent: Wednesday, May 09, 2007 10:59 AM
> To: TEITAC Web/Software Subcommittee
> Subject: Re: [teitac-websoftware] Contrast
>
> Gregg and I have had endless debates over this. We have evolved to the

> current compromise:
>
> Note 4: Background color is the specified color of content over which
> the text is to be rendered in normal usage. If no background color is
> specified, then white is assumed.
>
> Note 5: For text displayed over gradients and background images,
> authors should ensure that sufficient contrast exists for each part of

> each character in the content.
>
> I agree that the current wording not universally applicable.
> The fact that there is a formula in the provision shouldn't fool
> anyone into thinking this is automatically testable - it isn't. The
> idea is to give guidance as to what a reasonable contrast level is and

> to allow humans (developers and QA) to determine how to evaluate
> content.
>
> Sean Hayes
> Standards and Policy Team
> Corporate Accessibility Group
> Microsoft
> Phone:
> mob +44 7977 455002
> office +44 117 9719730
>
>
> -----Original Message-----
> From: = EMAIL ADDRESS REMOVED =
> [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of
> Andrew Kirkpatrick
> Sent: 09 May 2007 16:49
> To: TEITAC Web/Software Subcommittee
> Subject: Re: [teitac-websoftware] Contrast
>
> > Text (and images of text) have a contrast ratio of at least 5:1,
> > except if the text is pure decoration. Larger-scale text or
> images of
> > text can have a contrast ratio of 3:1.
> >
> > See 1.4.3 in WCAG 2.0 -
> > http://www.w3.org/WAI/GL/WCAG20/#visual-audio-contrast
>
> I wonder how this is to be evaluated in some situations. I see text
> that is over a multi-color or even image background often and not all
> of it strikes me as likely to be a problem to read. The contrast
> ratio formula doesn't seem to account for this - does it?
>
> AWK
>

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