Re: Situation B: Colors for stacked bar chart

On Wed, Aug 17, 2011 at 9:52 AM, <noreply@w3.org> wrote:

>
> Name: Makoto Ueki
> Email: makoto.ueki@gmail.com
> Affiliation: WAIC (Japan)
> Document: UW
> Item Number: Understanding Success Criterion 1.4.1
> Part of Item: Intent
> Comment Type: question
> Summary of Issue: Situation B: Colors for stacked bar chart
> Comment (Including rationale for any proposed change):
> Will SC 1.4.1 be applied to a stacked bar chart?
>
> For example, a stacked bar chart shows two items by using two different
> colors. There are the graph legends near the chart which explains what is
> represented by each bar and color. The patterns are not used.
>
> It might depend on the colors used in the chart. If the colors are black
> and white, will SC 1.4.1 be applied to the image of the stacked bar chart?
>
> In that case, the color differences are used to convey information within
> non-text content. However the patterns are not necessarily needed to convey
> the same information in a manner that does not depend on color. Because
> black and white has sufficient contrast ratio and brightness difference.
>
> Does SC 1.4.1 require the authors to include patterns to any combination of
> colors?
>
> If yes, could you explain the reason why the patterns are needed for black
> and white?
>
> Proposed Change:
> Need an answer from WCAG WG in order to harmonize JIS and WCAG 2.0.
>
> ================================
Response from the Working Group
================================
Yes. Lightness/darkness is independent of color and can be used to present
information in a manner that is "not color alone". Black and white is an
obvious example of something which is independent of color vision.

Unlike WCAG requirements for foreground text against a background, there are
no specific guidelines for how much lightness/darkness (or relative
luminosity) contrast there should be between two items in a chart. It would
seem to differ if they were separate vs if they were touching as in your
example. If touching, a contrast ratio of 3:1 is probably sufficient though
4.5:1 is better and 7:1 is best (but you cannot have three different colors
with that ratio.

Patterns can be used when there are more than two or three types of
information to be differentiated.

Loretta Guarino Reid, WCAG WG Co-Chair
Gregg Vanderheiden, WCAG WG Co-Chair
Michael Cooper, WCAG WG Staff Contact


On behalf of the WCAG Working Group