Re: User Needs - contrast sensitivity

Hi Jim,

Apologies that I couldn’t make today, project overload. On the contrast aspect, it doesn’t seem to answer the question people have been asking?

Logically (but without research) it seems that reading text is a harder task (visually and cognitively) than perceiving if a line or box is there.

So what we need is something that says either:

-          it is as difficult, or

-          it isn’t as difficult by this factor of difference.

I’m guess no one has tried to research this aspect?

Cheers,

-Alastair


From: Jim Allan <jimallan@tsbvi.edu>
Date: Thursday, 4 May 2017 at 15:25
To: LVTF - low-vision-a11y <public-low-vision-a11y-tf@w3.org>
Subject: User Needs - contrast sensitivity
Resent-From: LVTF - low-vision-a11y <public-low-vision-a11y-tf@w3.org>
Resent-Date: Thursday, 4 May 2017 at 15:26

All,
I have been doing a good bit of research related to the contrast discussions on Issues 9 & 10 (graphics contrast and UI controls contrast). I updated the research page with what I found.

In our user needs document the section on 2.4.3 Contrast Sensitivity needs a few additions. other sections of the document discuss which eye conditions have a particular impairment (acuity, glare, color, field, etc) and the functional problems caused by the impairment. 2.4.3 lacks this information. Updating 2.4.3 and the benefits section of Issue 9 & 10 should address the concerns raised in the comments on these items.

current 2.4.3:

Contrast sensitivity is the ability to detect differences in brightness, for example, to discern text from its background. A common accessibility barrier for people with low contrast sensitivity is gray text on a light background.

Contrast is based on brightness. Colors that look very different (for example, red, blue, green) can have similar brightness, and not provide sufficient contrast. Tools<https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast7.html#visual-audio-contrast7-resources-head> are available to determine the contrast ratio between colors.
new:

Contrast sensitivity is the ability to detect differences in brightness, for example, to discern text from its background. A common accessibility barrier for people with low contrast sensitivity is gray text on a light background. Contrast sensitivity decreases with age and is concomitant with many other vision diseases and conditions. Contrast levels should be the same for text, graphics, and controls.

Contrast is based on brightness. Colors that look very different (for example, red, blue, green) can have similar brightness, and not provide sufficient contrast. Tools<https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast7.html#visual-audio-contrast7-resources-head> are available to determine the contrast ratio between colors.

​Current Benefit section for Issues 9 & 10: ​

People with low vision often have difficulty perceiving graphics that have insufficient contrast. This can be exacerbated if the person has a color vision deficiency that lowers the contrast even further. Providing a relative luminance<http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef> (lightness) difference of 4.5:1 or greater can make these items more distinguishable when the person does not see a full range of colors and does not use assistive technology.

When non-text content is larger, a color contrast of 3:1 or greater can be sufficient for perception by people with moderately low vision.

In short, contrast levels should be the same for text, graphics, and controls.

--
Jim Allan, Accessibility Coordinator
Texas School for the Blind and Visually Impaired
1100 W. 45th St., Austin, Texas 78756
voice 512.206.9315<tel:(512)%20206-9315>    fax: 512.206.9264<tel:(512)%20206-9264>  http://www.tsbvi.edu/

"We shape our tools and thereafter our tools shape us." McLuhan, 1964