Potential update to G18 or new failure technique for SC 1.4.3 [SEC=UNCLASSIFIED]

Greetings WCAG 2.0 Working Group

Update to Technique G18
I would like to make a recommendation to update General Technique 18, or create a new failure technique for insufficient colour contrast on anti-aliased text, to help address Success Criterion 1.4.3.

The problem occurs for anti-aliased text which while having sufficient colour contrast on vertical strokes, has insufficient contrast on pixels in parts of the character (especially diagonal strokes or corners of letters). To support this case, I have included two images of a website which currently displays this anti-aliased text which in parts both passes and fails G18. The text in the image uses #545454 on #ffffff (has a ratio of 7.6:1, but in parts of the anti-aliased letters has a ratio of just 1.7:1). This is especially problematic when viewing the text at normal size, as the font appears fuzzy and not sufficiently visible.

This was noticed on this website: http://www.verseone.com/main.cfm?type=WEBACCESSIBILITY on 24/11/11. I tested in Firefox 7.0.1 and Internet Explorer 8, as well as the Colour Contrast Analyser (Vision Australia) and the Firefox plug-in WCAG Contrast checker 1.1.02.

The lack of sufficient colour contrast appears on anti-aliased text typically on light/fine or serif fonts, or on thin character parts such as in the letters k, e, w and o as well as some numbers.

Currently G18 notes: "Note: For aliased letters, use the relative luminance value found two pixels in from the edge of the letter."

I would add that for anti-aliased letters, that perhaps a wider sample (2x2 or 4x4 pixels) or sampling all of horizontal, vertical and diagonal stokes (for at least one character) should be taken to find a more accurate sampling of text colour. This would only likely be an issue for anti-aliased text below 14pt or not bold.

I welcome your review or comment on this issue.

Wrong link
As an aside, the second link to the  Techniques Submission Form, from the Techniques page (http://www.w3.org/TR/WCAG20-TECHS/) under "Status of This Document", actually points to a WCAG 1 conformance logo page. See: http://www.w3.org/WAI/WCAG1-Conformance


Thanks and kind regards


Ravenna Calais

Senior Policy Officer
Web Advice and Policy
Australian Government Information Management Office (AGIMO)
Department of Finance and Deregulation

p: 02 6215 2048 | e: raven.calais@finance.gov.au<mailto:raven.calais@finance.gov.au>
w: http://webguide.gov.au/



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