# Suggested edits for guidelines 1.4 CONTRAST

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Wed, 22 Feb 2006 01:38:23 -0600
To: <w3c-wai-gl@w3.org>
Message-ID: <001c01c63782\$f63bfb00\$ee8cfea9@NC6000BAK>
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Here are some suggested edits for the WCAG Contrast guideline Definitions

They are to clarify some ambiguous parts but do not change the guidelines.

Gregg

-- ------------------------------
Gregg C Vanderheiden Ph.D.
Professor - Ind. Engr. & BioMed Engr.
Director - Trace R & D Center
The Player for my DSS sound file is at http://tinyurl.com/dho6b

Note:  All modified content segments are enclosed in double braces {{}}

definition for "luminosity contrast ratio"

[old definition...]

luminosity contrast ratio
{{(L1+.05) / (L2+.05) where L is luminosity and is defined as .2126*R +
.7152*G + .0722B using linearized R, G, and B values. Linearized R (for
example) = (R/FS)^2.2 where FS is full scale value (255 for 8 bit color
channels). L1 is the higher value (of text or background) and L2 is the
lower value.}}

[end of old definition]

[new definition...]

luminosity contrast ratio
{{(L1 + 0.05) / (L2 + 0.05), where L1 is the luminosity of the lighter of
the text and background colors, and L2 is the luminosity of the darker of
the text and background colors.

The luminosity of a color is defined as 0.2126 * ((R / FS) ^ 2.2) + 0.7152 *
((G / FS) ^ 2.2) + 0.0722 * ((B / FS) ^ 2.2). R, G, and B are the red,
green, and blue RGB values of the color; FS is the maximum possible full
scale RGB value for R, G, and B (255 for eight bit color channels); and the
"^" character is the exponentiation operator.

Note: Luminosity values can range from 0 (black) to 1 (white), and
luminosity contrast ratios can range from 1 to 21.}}

[end of new definition]
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Received on Wednesday, 22 February 2006 07:38:24 GMT

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