W3C home > Mailing lists > Public > www-style@w3.org > October 2012

Re: Alternative Style Sheets

From: Gérard Talbot <www-style@gtalbot.org>
Date: Sat, 13 Oct 2012 22:21:34 -0400
Message-ID: <5d93783e20355ba2adc8b2e25a910971.squirrel@ed-sh-cp3.entirelydigital.com>
To: "Antony Kennedy" <antony@silversquid.com>
Cc: "Markus Ernst" <derernst@gmx.ch>, "www-style@gtalbot.org" <www-style@gtalbot.org>, "Dirk Schulze" <dschulze@adobe.com>, "www-style@w3.org" <www-style@w3.org>

Le Sam 13 octobre 2012 5:41, Antony Kennedy a écrit :
> More than that, there is no colour scheme that will satisfy all
> requirements. Even if you follow WCAG guidelines.
> Sent from my iPhone

Anthony, I respectfully disagree with you.

Checkpoint 2.2 - Ensure that foreground and background color combinations
provide sufficient contrast when viewed by someone having color deficits
or when viewed on a black and white screen
Technique 2.2.1 [priority 3] Test the color attributes of the following
elements for visibility:

Two colors provide good color visibility if the brightness difference and
the color difference between the two colors are greater than a set range.

Color brightness is determined by the following formula:
((Red value X 299) + (Green value X 587) + (Blue value X 114)) / 1000
Note: This algorithm is taken from a formula for converting RGB values to
YIQ values. This brightness value gives a perceived brightness for a

Color difference is determined by the following formula:
(maximum (Red value 1, Red value 2) - minimum (Red value 1, Red value 2))
+ (maximum (Green value 1, Green value 2) - minimum (Green value 1, Green
value 2)) + (maximum (Blue value 1, Blue value 2) - minimum (Blue value 1,
Blue value 2))

The rage (sic) for color brightness difference is 125. The range for color
difference is 500.
Techniques For Accessibility Evaluation And Repair Tools

And there are other color contrast analyzer algorithms which are
furthermore accessible. I read - but can not remember where - that Xerox
had color constrast algorithms furthermore accessibility-friendly.

about 8% of the male population have some form of color deficiency
Can Color-Blind Users See Your Site?

As far as big enough font-size, humans have a 2000 years experience of
usability and printed material.

For color constrast, humans have a 50,000 - 100,000 years experience in
usability. The first drawings of deers, horses and other animals in caves
by Cro-Magnons were meeting, were most likely passing those color contrast

CSS 2.1 Test suite RC6, March 23rd 2011

Contributions to CSS 2.1 test suite

Web authors' contributions to CSS 2.1 test suite
Received on Sunday, 14 October 2012 02:22:03 UTC

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