WebAIM - Web Accessibility In Mind

E-mail List Archives

Re: Color Contrast Question

for

From: Jared Smith
Date: Sep 20, 2017 10:43AM

The WCAG formula generates the contrast ratios, but these don't align to a
percent or "times darker" value. The minimum is 1:1 and the maximum is
21:1. Your logic would suggest that 1:1 (white on white) means white is one
times darker than white, and black on white means black is 21 times darker
than white. That doesn't work. Your phrasing also wouldn't consider light
text on a black background. And the ratios are not linear - 4:1 is not
twice as much contrast as 2:1, for example.

In reality the formula doesn't consider many aspects of true contrast and
perception. WebAIM and others are trying to influence a reconsideration of
this formula and perhaps the WCAG pass/fail thresholds to better align them
with human perception. With that said, the WCAG ratios do give a relatively
accurate measure of *luminance* contrast - and that's pretty important. If
your colors fall well below the WCAG thresholds, they'll be difficult for
most anyone to read.

Jared Smith





On Wed, Sep 20, 2017 at 8:44 AM, JP Jamous < <EMAIL REMOVED> > wrote:

> Folks,
>
>
>
> I want to be able to breakdown 4.5:1 and 3:1 into a simple way. Is it
> correct to state the following?
>
>
>
> 4.5:1 means that the foreground color should be 4 and a half times darker
> or
> lighter than the background color to be seen properly by people with low
> vision individuals.
>
> 3:1 means that the foreground color should be 3 times darker or lighter
> than
> the background color to be seen properly by people with low vision
> individuals.
>
> If I am wrong can you correct me please?
>
>
>
> ---
> This email has been checked for viruses by AVG.
> http://www.avg.com
> > > > >