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Color & contrast- response to Lee's message

From: john_slatin <john_slatin@forum.utexas.edu>
Date: Wed, 17 Apr 2002 09:00:50 -0500
Message-ID: <6AC4E20EED49D411941400D0B77E52F0069396DD@forum.cc.utexas.edu>
To: "'Web Content Guidelines'" <w3c-wai-gl@w3.org>
I meant to send this to the list yesterday and not just to Lee, but
evidently hit 'Reply' instead of 'Reply-all'.
==Message begins==
Lee, thanks for the Microsoft reference.  I assume that the snippet below is
what you're referring to as grounds for the statement that text should
be darker than the background:
"It is clear to everybody that black text on a white background is extremely
easy to see, which is part of the reason why most of the printed material
read is black text on a white background. Likewise, white on black produces
high contrast, but it is more difficult to read because black is perceived
as being heavier than white and, thus, squeezes it out a little. "
I'm sure this is true for most people, especially those with so-called
normal vision. I am equally certain, however, that *some* people with
limited vision
find it far easier to read light text against a dark background.  If for
example you look at CCTV (closed circuit TV) systems that display magnified
of print material on computer and/or TV screens, you'll find that many of
them have switches that allow users to choose between dark on light and
on dark, as well as choosing different color combinations.  The same is true
for many software based screen magnifiers such as AI Squared's ZoomText. 
And Kara Pernice Coyne and Jakob Nielsen report in _Beyond ALT Text_
(Nielsen-Norman Group, 2001) that users with low vision often switched back
and forth
between "normal" and "inverted" video (i.e., between dark on light and light
on dark) to ease eyestrain and fatigue.  I used to do that when I could
see enough for ZoomText and CCTV to be worth the trouble.  And I used to use
MS Word's settings to display white text on a blude background-- the option
was there to ensnare Word Perfect users for whom those were the default
colors, but it was good for me, too.  I finally had to stop because JAWS
handle it any more....
So perhaps the success critierion should involve giving users the ability to
choose between light on dark and dark on light, and to make that choice
available rather than a one-shot deal.
Sorry for length of message.
John Slatin, Ph.D.
Director, Institute for Technology & Learning
University of Texas at Austin
FAC 248C, Mail code G9600
Austin, TX 78712
ph 512-495-4288, f 512-495-4524
email jslatin@mail.utexas.edu <mailto:jslatin@mail.utexas.edu> 
web http://www.ital.utexas.edu <http://www.ital.utexas.edu/> 
Received on Wednesday, 17 April 2002 10:01:00 UTC

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