Fwd: Re: contrast of borders vs text

---------- Forwarded message ----------
From: "Gordon Legge" <legge@umn.edu>
Date: Jun 14, 2017 5:48 PM
Subject: Re: contrast of borders vs text
To: "Jim Allan" <jimallan@tsbvi.edu>, "Wayne Dick" <wayneedick@gmail.com>,
"legge" <legge@umn.edu>

Hi Jim,

Here are a few quick comments. I'd be happy to elaborate, or discuss by
phone. I'm leaving for  travel  to  Europe on Saturday, so follow-up might
have to wait until I return in early July.

Text could be "harder" than form controls for several reasons:

1) because of the non-visual cognitive or linguistic demands;

2) because text is often small and may be viewed near the acuity limit
(especially in low vision)

3) and because text is "crowded" in the sense of near proximity of
neighboring letters.

All that being said:

Sometimes form controls can be small, and viewed near the acuity limit.

Sometimes form controls can be "crowded," that is, there are neighboring
visual objects.

If we equate individual text letters and form controls for visual size and
proximity of nearby images, there is no reason to believe that contrast
demands will be different.

In fact, one could make the argument that poor contrast can be a greater
problem for form controls. Text is usually binary--black on white. As long
as any part of the text  character is above threshold, the whole symbol is
likely to be above threshold. Sometimes, form controls use grayscale
coding. Even if the bounding contour is above the viewer's contrast
threshold, it may be the case that information coded with grayscale shading
may be below threshold.

Bottom line: Contrast requirements for form controls should be equivalent
to contrast requirements for text.

I hope these comments help.


On 6/13/2017 1:24 PM, Jim Allan wrote:

> Hi Gordon,
> Greg Goodrich, a colleague of mine for many years suggested I ask you
> about this topic. I also work with Wayne Dick on the Low Vision Task Force,
> which is trying to create some guidelines for web authors to help them make
> websites that are more accessible to folks with low vision.
> The taskforce is working on criteria for contrast of outlines of form
> controls etc. see https://github.com/w3c/wcag21/issues/10 <
> https://github.com/w3c/wcag21/issues/10> for information.
> The Task Force believes that border/outline contrast should be the same as
> text contrast.
> Those not on the task force say, without research,  that reading text is a
> harder task (visually and cognitively) than perceiving whether a line or
> box is there (such as a form box or line).____
> ____
> Is there any research that indicates either:____
> -          it is as difficult, or____
> -          it isn’t as difficult by X factor of difference.____
> ____
> I have spent hours reading research on the web, but can only find
> information on text and contrast. Do you know of any research related to
> line/outline perception and contrast?
> --
> Jim Allan, Accessibility Coordinator
> Texas School for the Blind and Visually Impaired
> 1100 W. 45th St., Austin, Texas 78756
> voice 512.206.9315    fax: 512.206.9264 http://www.tsbvi.edu/
> "We shape our tools and thereafter our tools shape us." McLuhan, 1964

Received on Wednesday, 14 June 2017 23:25:21 UTC