Re: Colour contrasts (was: WCAG2 Conformance Questions)

Colour Contrast Analyser Firefox Extension
http://juicystudio.com/article/colour-contrast-analyser-firefox-extension.php

Colour Contrast Analyser windows and MAC apps
http://www.paciellogroup.com/resources/contrast-analyser.html

regards
stevef

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.
>
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-- 
with regards

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

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