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Re: Graphics contrast - critical principle

From: Alastair Campbell <acampbell@nomensa.com>
Date: Wed, 7 Dec 2016 00:54:27 +0000
To: James Nurthen <james.nurthen@oracle.com>, "w3c-wai-gl@w3.org" <w3c-wai-gl@w3.org>
Message-ID: <HE1PR0901MB14667F38F7A9FC93E7A07AFCB9850@HE1PR0901MB1466.eurprd09.prod.outlook.com>
> Example 2 in here is really confusing me.  Can you explain how this differs from 1.4.3 as I believe the text in this image is already covered by WCAG.

Hi James,

A good point, thankfully one that doesn't undermine the concept! 

The example was to show what you need to discern to understand the image.

For example 2, it is the proportions of market share for each browser that you need to understand, and the numbers are 'discernable' (apart from the over-lapping text which I'm ignoring for the sake of this example).

You can consider example 2 as one where you put NA for this SC, and pass under 1.4.3 (I'll update the page).

However, the first example on that page, and examples 1-4, 7, 8, 10, 12, and 13 on the original test page do not (by)pass the SC on this method:
https://alastairc.ac/tests/graphic-contrast-test.html

NB: To get some quick examples I was googling things like "line chart" and filtering for re-use-rights! The examples on the original page are better, but several are from just before the election and I didn't want to bring that up again... Sorry!

Another way to put it would be: If you rely on the graphic to convey information, then it needs to be discernable. Then each element within the graphic that you need to discern to understand it has to have sufficient contrast.
When you go through lots of examples, it turns out that labelling & text values are really useful for conveying information!

As Bruce pointed out, if you have multiple colours together you can't have more than 3 and meet 4.5:1, and even at 3:1 you run out pretty quickly.

However, there are many ways to provide sufficient contrast that either bypass or meet this SC, including:
- Using labels and/or values (although you might run afoul of SC 1.4.5).
- Having gaps or borders between pie-slices or the things that need contrast (see examples 10-12 on the page linked above.)

And probably more methods, but it's late and I'll come back to this tomorrow.

Thanks for having a look, I really want to nail this concept before tackling the easier aspects.

Cheers,

-Alastair 
Received on Wednesday, 7 December 2016 00:55:03 UTC

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