# Re: Situation B: Colors for stacked bar chart

• From: Makoto UEKI - Infoaxia, Inc. <makoto.ueki@gmail.com>
• Date: Sun, 23 Oct 2011 09:11:00 +0900
• To: Loretta Guarino Reid <lorettaguarino@google.com>
• Message-ID: <CAF9hGuYuL0ELPMHf=Y7E=gSO_7irjfZYk7p=ASJYupf50orDuw@mail.gmail.com>
```Hi Loretta,

Thank you very much for your response. I have additional questions to
make points clearer.

Q1.
My understanding is that, if two items in a chart are touching, a
contrast ratio of 3:1 is required (4.5:1 is better and 7:1 is best)
and patterns are not required as the chart which has the contrast
ratio presents information in a manner that is "not color alone". Am I
correct?

Q2.
What about if two items in a chart are separate?

Q3.
If there are three items in a chart, patterns should be used as we
cannot have three different colors with that ratio.
Am I correct?

- Makoto

> 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
```

Received on Sunday, 23 October 2011 00:11:35 UTC