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Re: measuring contrast ratio and Windows Clear Type

From: Marc Haunschild <mh@zadi.de>
Date: Mon, 11 Aug 2014 12:24:43 +0200
Message-ID: <53E899EB.8060802@zadi.de>
To: w3c-wai-ig@w3.org
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. ;-)


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
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Telefon: +49 (0)228 996845-7324
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E-Mail: marc.haunschild@ble.de
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Received on Monday, 11 August 2014 10:25:14 UTC

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