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RE: measuring contrast ratio and Windows Clear Type

From: Jim Tobias <tobias@inclusive.com>
Date: Mon, 11 Aug 2014 09:45:56 -0400
To: "'Greg Kraus'" <greg_kraus@ncsu.edu>, <w3c-wai-ig@w3.org>
Message-ID: <107101cfb56a$94028e30$bc07aa90$@inclusive.com>
Very interesting, Greg -- thanks for making that tool.

I'm not a vision scientist, but something tells me we need their input to make sure that our tools reflect that actual user needs. I think a vision scientist was involved in the original contrast algorithm, and maybe we're ready for a second pass, that looks at how low vision works above the pixel and multi-pixel level.

***
Jim Tobias
Inclusive Technologies
+1.908.907.2387 v/sms
skype jimtobias
  

> -----Original Message-----
> From: Greg Kraus [mailto:greg_kraus@ncsu.edu]
> Sent: Monday, August 11, 2014 8:11 AM
> To: w3c-wai-ig@w3.org
> Subject: Re: measuring contrast ratio and Windows Clear Type
> 
> I developed a tool to deal with issues like this. It's a Chrome
> extension called Color Contrast Analyzer.
> 
> https://chrome.google.com/webstore/detail/color-contrast-analyzer/dagdlcijhfbmgkjokkjicnnfimlebcll?hl=en
> 
> It takes a screen shot and compares a pixel with every pixel around
> it. You can set how wide of a radius you want to search around each
> pixel in order to deal with issues like anti-aliasing. The resulting
> image shows each pixel that has an adjacent pixel with enough contrast
> with the original pixel. In the end, the tool creates outlines in the
> page of what I call "contrast borders" that show where the contrast
> exceeds the given WCAG conformance level.
> 
> It lets you choose between AA and AAA, and also for standard sized
> text or medium-bold/larger text. The tool does require you to know
> what size text you are analyzing because it is simply doing pixel
> analysis. It has no idea what it is actually analyzing.
> 
> Another result of this is it will analyze contrast in images too.
> While contrast in images is not a WCAG requirement, it comes in handy
> when you need to analyze text in a picture, which is a WCAG
> requirement.
> 
> Greg
> --
> Greg Kraus
> University IT Accessibility Coordinator
> NC State University
> 919.513.4087
> gdkraus@ncsu.edu
> 
> On Mon, Aug 11, 2014 at 6:24 AM, Marc Haunschild <mh@zadi.de> wrote:
> > Hi Jan,
> >
> > I can just describe my practice: when I measure contrast with cca I try to
> > find a quite dark pixel (on light background) - normally this has less
> > contrast than the colors defined in the CSS.
> >
> > If the contrast is not high enough, I recommend to change the colors.
> >
> > Of course this is not for official testing (like in BITV-Test), but for real
> > life accessibility I think it is a good compromise.
> >
> > Reasons: On the one hand a user is able to change the Clear Type value
> > himself or to use a bigger font, on the other hand the author of the web
> > site improves the accessbility a little bit more than WCAG aks him to do.
> >
> > To me accessibilty is a matter of fairness and to me it seems to be fair,
> > the way I measure contrast. So I do it this way. ;-)
> >
> > Marc
> >
> >
> > Am 11.08.14 12:05, schrieb Joe Chidzik:
> >
> >> Whenever I've used the CCA with IE, fonts appear anti-aliased, meaning it
> >> is not clear which pixel to pick for the actual text colour. Firefox does
> >> not exhibit this problem for me, and so I've always used Firefox when
> >> measuring contrast with the CCA just to be sure I'm selecting the colours
> >> specified by the CSS.
> >>
> >> I don't know if it's possible to detect (via CSS\JavaScript) if a user has
> >> clear type enabled or not, but in my view, measuring the contrast via the
> >> values provided in the CSS should be all that it is required to check
> >> adherence to the success criteria.
> >>
> >> Joe
> >>
> >>
> >>> -----Original Message-----
> >>> From: Jan Eric Hellbusch [mailto:hellbusch@2bweb.de]
> >>> Sent: 11 August 2014 10:45
> >>> To: w3c-wai-ig@w3.org
> >>> Subject: measuring contrast ratio and Windows Clear Type
> >>>
> >>> Hi,
> >>>
> >>> I was giving a seminar the other day on Web accessibility testing and was
> >>> asked
> >>> by one of the participants how I measure contrast when clear type is
> >>> activated. I
> >>> was caught by surprise, because I had switched it off when setting my
> >>> Windows 7
> >>> laptop up a couple of years ago and I never gave it a second thought.
> >>> Since then I
> >>> have been measuring contrast ratios with clear type switched off.
> >>>
> >>> I have been trying to find more detailed information on the precise
> >>> differences in
> >>> measuring contrast ratios with and without clear type on Windows, but I
> >>> obviously
> >>> have the wrong search terms. Perhaps someone on this list can point me
> >>> out in
> >>> the right direction?
> >>>
> >>> * Using CCA there is the possibility of grabing several pixels at a time.
> >>> Does that solve the problem of measuring a correct contrast ratio?
> >>> * Or do I have to switch clear type off or  (in Firefox) set
> >>> gfx.content.azure.enabled
> >>> to false?
> >>>
> >>> I would greatly appreciate a hint or a resource.
> >>>
> >>> Thanks,
> >>> Jan
> >>>
> >>> --
> >>> Jan Eric Hellbusch
> >>> Tel.: +49 (231) 33005825 oder +49 (163) 3369925
> >>> Accessibility-Beratung: http://2bweb.de
> >>> Blog: www.chemnitzer-14.de
> >>> Bücher, Artikel: www.barrierefreies-webdesign.de
> >>>
> >>>
> >>>
> >>
> >>
> >
> >
> >
> > --
> > Mit freundlichen Grüßen,
> >
> > i. A. Marc Haunschild
> > Zugängliche Anwendungsentwicklung und Qualitätskontrolle
> > ________________________________________
> > Referat 414 / Abteilung 4
> > Bundesanstalt für Landwirtschaft und Ernährung
> > Deichmanns Aue 29, 53179 Bonn
> > Telefon: +49 (0)228 996845-7324
> > Fax: +49 (0)228 6845-3101
> > E-Mail: marc.haunschild@ble.de
> > Internet: www.ble.de ( http://www.ble.de/ )
> >
Received on Monday, 11 August 2014 13:46:33 UTC

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