An advisory on anti-aliased fonts.

Name: Mary Frances Laughton
Email: Laughton.MaryFrances@ic.gc.ca
Affiliation: Government of Canada
Document: UW
Item Number: Understanding Success Criterion 1.4.3
Part of Item: Additional Techniques (Advisory)
Comment Type: technical
Summary of Issue: An advisory on anti-aliased fonts.
Comment (Including rationale for any proposed change):
This comment also applies to 1.4.5 and may also apply to the Techniques Document.



While the requirement for using a formula to assure a sufficient foreground/background luminosity ratio is clear for solid color elements, and even reasonable for most dithered elements against solid or dithered elements (i.e. through averaging dithered values), one situation should be highlighted as an advisory: anti-aliased fonts especially at small default sizes can be very difficult for some people with reduced visual acuity to distinguish from background even if the “average” contrast ration appears within range.  At small sizes, even a black stroke core can be rendered as a lighter gray by the anti aliasing dither: moving out from the core the pixel become lighter still.  In the particular example that brought this comment a small anti-aliased font was set against a white background.  Two evaluators, one with low vision, and one with 50-year-old eyes had great difficulty reading the text until it had been enlarged (e.g. using Internet Explorer 7’s “Change Zoom Level” control to 150% enlargemnt). The Understanding Success Criterion 1.4.3 and 1.4.5 entries mention: “Note 3: Text can be evaluated with anti-aliasing turned off” we do not feel that this provides designers with sufficient information about the use of small dithered font colors.

Proposed Change:
GoC recommends adding a discussion and/or examples to illustrate this problem.

Received on Friday, 29 June 2007 21:12:57 UTC