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Re: Graphics contrast - critical principle

From: Alastair Campbell <acampbell@nomensa.com>
Date: Thu, 8 Dec 2016 21:36:38 +0000
To: David MacDonald <david100@sympatico.ca>
CC: GLWAI Guidelines WG org <w3c-wai-gl@w3.org>
Message-ID: <82489ACE-11EE-49AB-ADA1-F12019CA17C9@nomensa.com>
David wrote:
> Should we be requiring the image have contrast with the background on all sides or just one or some sides.... ?
 
 As it stands, the SC text [1] says you test “against their immediate surrounding background”, which is defined as:
“a 3px area adjacent to the entire length of the outer perimeter of the element.”
 
I think this could be refined, partly because it implies you have to test every side (a), and partly because the 3px clashes with the thick/thin concept (b).
 
a) In the pie chart example [1 under examples], the bit you need to discern to understand is the contrast between each slice, the contrast against the outside of the pie is not (that) important. There are other places where understanding can be gained from the contrast between two things but not a third. Difficult to do in SC text though.

b) I’m not sure where the 3px around the graphic came from originally (Glenda?), but I would like to use the same logic of the thick/thin aspect. If the adjacent shape/line is under 3px, that’s fine, but it needs the stronger contrast level. The last pie chart example is a good illustration of that.
 
To achieve (b) I think we can just remove the word ‘background’, so you test “against their immediate surrounding”.
 
To achieve (a) is harder, I can't see how to adjust this: "are essential for understanding the content" to say that you only have to test the sides needed for understanding?

Kind regards,

-Alastair
 
1] https://www.w3.org/WAI/GL/low-vision-a11y-tf/wiki/index.php?title=Informational_Graphic_Contrast_(Minimum)&oldid=2609
 
Received on Thursday, 8 December 2016 21:37:16 UTC

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