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CSS3 Color tests: font smoothing/anti-aliasing may result in apparent test failure

From: Sylvain Galineau <sylvaing@microsoft.com>
Date: Fri, 15 Jan 2010 23:32:36 +0000
To: "public-css-testsuite@w3.org" <public-css-testsuite@w3.org>
Message-ID: <045A765940533D4CA4933A4A7E32597E102E11C4@TK5EX14MBXC113.redmond.corp.microsoft.com>
At least two CSS3 Color testcases compare an RGB foreground color with an RGBA equivalent:

http://www.w3.org/Style/CSS/Test/CSS3/Color/current/html4/t040202-rgba-a0-6-a.htm
http://www.w3.org/Style/CSS/Test/CSS3/Color/current/html4/t0302-opacity-basic-0-6-a.htm

Both testcases verify that rgb(102,102,102) looks like either rgba(0,0,0,0.6) or rgb(0,0,0) with 0.6 opacity. 
This works fine with background colors but may be problematic for UAs that apply anti-aliasing and other 
font smoothing algorithms since the output of the latter will vary depending on the text color. In this case, the rgba() 
version of the text may end up looking darker than expected since the font smoothing code will initially run on black text 
against a white background. Subsequently applying alpha on the smoothed text will thus not look identical to smoothing 
rgba(102,102,102,1) text. 
Received on Friday, 15 January 2010 23:33:13 GMT

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