Re: Situation B: Colors for stacked bar chart

Hi Makoto,

	There are no contrast requirements for charts.  
	The only WCAG requirements for contrast are for text. 

	The contrast ratio's of 3:1, 4.5:1 and 7:1 were just suggestions for making the bars in a chart be different from each other.  So you can see that they are different.

	If the bars touch it is easier to tell them apart.  Also - their relative position would provide additional cues. 
	If they are separate it is harder so the difference might need to be more. And the distance between the bars would also have some effect.  But there are no defined criteria for amount of difference.  

	Patterns are another means - and can be used when there are too many different bars or lines to tell the difference between them.

	However there are no set contrast requirements for charts or anything other than text. 



On Oct 22, 2011, at 7:11 PM, Makoto UEKI - Infoaxia, Inc. wrote:

> 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
> 
> 
> 2011/10/21 Loretta Guarino Reid <lorettaguarino@google.com>:
>> 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
>