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Re: colour contrast algorithm


From: gez
Date: Sep 18, 2003 6:12AM

Hi Dey,

I've been trying to find out myself if there has been any more work on the
algorithm, but haven't been able to come up with anything.

Personally, I think the suggested algorithms works well, but I think the
threshold for the difference in colour is a bit high. I know that HP use the
algorithm, but instead of using a threshold of 500 for the colour
difference, they use a colour difference of 400, which is much more
workable. The W3C's threshold for the difference in brightness seems to work
OK from the tests I've done.

The algorithms only really work with normal text, and don't take into
account the weight of the font. You get the same results for bold or normal
text, where bold text will obviously be more distinguishable.

I've implemented the algorithm on my site, so you can quickly test colours
to see what works: http://www.juicystudio.com/services/colourcontrast.asp

Best regards.


----- Original Message -----
From: "Dey Alexander" < <EMAIL REMOVED> >
To: "Webaim forum" < <EMAIL REMOVED> >
Sent: Thursday, September 18, 2003 9:38 AM
Subject: colour contrast algorithm

> The suggested algorithm for testing to see if text and background
> colours provide sufficient contrast (as documented in the W3C's draft
> techniques document for Accessibility Evaluation and Repair Tools at
> http://www.w3.org/TR/AERT#color-contrast) has recently been discussed on
> this list (between 20-26 August 2003).
> However the discussion did not lead anywhere terribly useful, and my
> query is slightly different to the original focus of the earlier
> The W3C document indicates that the algorithm is a "suggested" one that
> is "still open to change". Can anyone shed any light on whether this is
> then a reliable indicator of colour contrast, or whether some more
> authoritative/reliable algorithm exists?
> Reason for my question: sponsors/clients of a project I am currently
> working on believe that the requirements are too stringent. This view
> was expressed after I used the algorithm to generate a report on a range
> of colour options that were being considered--very few of them passed
> muster, as I expected.
> I would be extremely grateful for any advice or references to other
> resources/expert opinions.
> Cheers,
> Dey
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