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Re: Colour contrasts (was: WCAG2 Conformance Questions)

From: Steven Faulkner <faulkner.steve@gmail.com>
Date: Fri, 22 Aug 2008 15:43:09 +0100
Message-ID: <55687cf80808220743j6a0ab2e3ma09d5b57078cc842@mail.gmail.com>
To: "Gregg Vanderheiden" <gv@trace.wisc.edu>
Cc: "David Woolley" <forums@david-woolley.me.uk>, "wai-ig list" <w3c-wai-ig@w3.org>

Colour Contrast Analyser Firefox Extension

Colour Contrast Analyser windows and MAC apps


2008/8/21 Gregg Vanderheiden <gv@trace.wisc.edu>:
> there are contrast tools available as a plug in tool for Firefox.   They may
> also create one for your platform if you approach them.
> I would check with faulkner.steve@gmail.com
> Gregg
> -----------------------
> Gregg Vanderheiden Ph.D.
> Director Trace R&D Center
> Professor Ind and Biomed Engr
> University of Wisconsin-Madison
> On Aug 21, 2008, at 5:11 PM, David Woolley wrote:
> Peter Thiessen wrote:
> ORCA.  But as for contrast testing, an automated tool, or any sort of tool
> would be helpful start. Or hell, even a few examples wouldn't hurt.
> What the formulae are doing is converting the image to greyscale and
> then requiring a certain ratio between the absolute intensities of
> adjacent shades of grey.  The numerator and demoninator are offset
> slightly so that you need a significant difference at low intensities.
> Unfortunately image manipulation tools don't seem to provide an sRGB to
> linear conversion function, so you will need to perform a gamma
> correction (mid level slider, or gamma function), then simply convert
> the result to grayscale.  (sRGB isn't a gamma curve at low intensities.)
> The one thing that this doesn't automate is looking the the contrasts in
> the resulting grayscale image.  To this subjectively, you should first
> convert back to the colour profile of your monitor.
> The complexity in doing the greyscale conversion is in that it does it
> reasonably accurately, whereas your image manipulation tool probably
> goes straight into the weighted sum.
> --
> David Woolley
> Emails are not formal business letters, whatever businesses may want.
> RFC1855 says there should be an address here, but, in a world of spam,
> that is no longer good advice, as archive address hiding may not work.

with regards

Steve Faulkner
Technical Director - TPG Europe
Director - Web Accessibility Tools Consortium

www.paciellogroup.com | www.wat-c.org
Web Accessibility Toolbar -
Received on Friday, 22 August 2008 14:43:44 UTC

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