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Your comments on WCAG 2.0 Last Call Working Draft of December, 2007

From: Loretta Guarino Reid <lorettaguarino@google.com>
Date: Mon, 10 Mar 2008 17:19:07 -0700
Message-ID: <824e742c0803101719v45d8ea67sb7e94c2a2a9a05d6@mail.gmail.com>
To: "Jane Berliss-Vincent" <jbvincent@cforat.org>
Cc: public-comments-WCAG20@w3.org

Dear Jane BerlissVincent,

Thank you for your comments on the 11 Dec 2007 Last Call Working Draft
of the Web Content Accessibility Guidelines 2.0 (WCAG 2.0
http://www.w3.org/TR/2007/WD-WCAG20-20071211). The WCAG Working Group
has reviewed all comments received on the December draft. Before we
proceed to implementation, we would like to know whether we have
understood your comments correctly and whether you are satisfied with
our resolutions.

Please review our resolutions for the following comments, and reply to
us by 31 March 2008 at public-comments-wcag20@w3.org to say whether
you accept them or to discuss additional concerns you have with our
response. Note that this list is publicly archived.

Please see below for the text of comments that you submitted and our
resolutions to your comments. Each comment includes a link to the
archived copy of your original comment on
http://lists.w3.org/Archives/Public/public-comments-wcag20/, and may
also include links to the relevant changes in the WCAG 2.0 Editor's
Draft of 10 March 2008 at

Note that if you still strongly disagree with our resolution on an issue,
you have the opportunity to file a formal objection (according to
3.3.2 of the W3C Process, at
to public-comments-wcag20@w3.org. Formal objections will be reviewed
during the candidate recommendation transition meeting with the W3C
Director, unless we can come to agreement with you on a resolution in
advance of the meeting.

Thank you for your time reviewing and sending comments. Though we
cannot always do exactly what each commenter requests, all of the
comments are valuable to the development of WCAG 2.0.


Loretta Guarino Reid, WCAG WG Co-Chair
Gregg Vanderheiden, WCAG WG Co-Chair
Michael Cooper, WCAG WG Staff Contact

On behalf of the WCAG Working Group

Comment 1: SC 1.4.3 - Step backwards from WCAG 1.0?
Source: http://lists.w3.org/Archives/Public/public-comments-wcag20/2008Jan/0055.html
(Issue ID: 2433)
Original Comment:

In using the new version of the Colour Contrast Analyzer, which
permits analysis via both the WCAG 1.0 or 2.0 criteria, I've found
instances where questionable color combinations passed at both the AA
and AAA levels using the new criteria, but failed using the old.

Proposed Change:
Assuming that the Analyzer tool is reliable, this suggests a need for
more stringent criteria in terms of higher contrast ratios. Thanks.
(BTW, I very much like that WCAG 2.0 no longer distinguishes between
bitmapped and regular text for this guideline.)

Response from Working Group:

The WCAG 2.0 contrast algorithm does not test for good color
combinations, just for those combinations with sufficient contrast
(based on brightness or relative luminance).

The new WCAG 2.0 algorithm was chosen because it is much more
consistent in its results. For one thing the old algorithm was
calculated in non-linear color space while the new algorithm is
calculated in in linear terms.  There is no way to correctly calculate
contrast in non-linear space. It will give you irregular results (good
results in some areas of the color space and bad results in others).

The new WCAG 2.0 rule also is based on luminance contrast alone -
whereas the old measure included color contrast as well.  This causes
the old algorithm to fail things that have plenty of visual contrast
for people with all types of color limitation.  For example some color
combinations will fail the old tool even though they are eminently
readable and have a luminance contrast of 15:1 or more  (where 21:1 is
pure black on white).   Very dark charcoal gray on yellow (contrast
ratio of 16:1) would fail the old algorithm. 100% green on black (same
as old CRTs) (contrast ratio of 15:1) would also fail the old

Having said all that, the new contrast ratio was chosen to be somewhat
less stringent than the old - in order to provide a larger color
palette for authors who are trying to meet the provision.

IN SUMMARY: The new algorithm is a better overall algorithm. However,
the values chosen for use with the new algorithm (5:1) do result in a
somewhat less strict level for some color combinations. This was done
to allow a somewhat less restricted number of colors when creating
pages that could meet the criterion.  However, the new criterion is
more strict than the old in some areas, but it is much more consistent
in its results. For one thing, the old algorithm was calculated in
non-linear color space while the new algorithm is calculated in in
linear terms which better match vision.
Received on Tuesday, 11 March 2008 00:19:23 UTC

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