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Thread: RE: sufficient color contrast
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From: ED COHEN
Date: Mon, Aug 25 2003 2:08PM
Subject: RE: sufficient color contrast
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The algorithm:is all well and good for text and backgrounds, but what about images?
As the W3C says, "Ideally, images and multimedia object should also be tested for color visibility but algorithms are beyond the scope of this specification." So what's a body to do?
According to our IT folks, my SVGA ViewSonic G800 monitor driver willnot permit me to go monochrome. It only allows me to adjust color temperature and they aren't all that keen on me fooling with that. Do I need to find a 1980's version PC and monitor?
Are people checking graphics for for color contrast and brightness and if so, how are you doing it?
>>> = EMAIL ADDRESS REMOVED = 8/20/03 5:49:25 PM >>>
John Britsios [SMTP: = EMAIL ADDRESS 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