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RE: sufficient color contrast


From: Marek Prokop
Date: Aug 20, 2003 4:59PM

John Britsios [SMTP: <EMAIL REMOVED> ] wrote:

> If I got your message right,...

Ok, once again ;-) Let me first quote The Techniques For
Accessibility Evaluation And Repair Tools, Technique 2.2.1:

( http://www.w3.org/TR/AERT#color-contrast )

Color visibility can be determined according to the following

(This is a suggested algorithm that is still open to change.)

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)) /
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.

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 for color brightness difference is 125. The range for
color difference is 500.

Now the question: do you consider the color brightnes difference
of 125 sufficient? I suggest it isn't sufficient because it
makes less than 50% brightness difference and I believe that the
safe difference is about 80% or more. What's your opinion?



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