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Re: Graphics contrast

From: Alastair Campbell <acampbell@nomensa.com>
Date: Wed, 16 Nov 2016 17:59:41 +0000
To: Jim Allan <jimallan@tsbvi.edu>, Glenda Sims <glenda.sims@deque.com>
CC: public-low-vision-a11y-tf <public-low-vision-a11y-tf@w3.org>
Message-ID: <57A2847F-53B3-4DED-BD2E-D491A7E1F9FD@nomensa.com>
Hi Jim, Glenda,

I think we need to be clearer about the unit of a ‘graphical element’ for the second case.

In the first case of dark grey on light, you need to understand the lid and can make up one element. For that element as a whole it is thicker then 3px, and passes the contrast aspects.

For the second example (which I realise is contrived but I know what you mean), the colours and pattern separate the lid from base, so it is now two graphical elements and each would have to pass. So if the lid was under 3px and 4.5:1 it would fail, and the base would need its least contrasting colour to have contrast with the surrounding.

The second example could be wrapped in a contrasting border to pass, but otherwise it should be treated the same as having a gradient – you pick the least contrasting bit of the whole element to test.

We could possibly bring in the definition of “gestalt” [1] to help define what an element is? It is murky territory though, I think Wayne had a definition of elements from a computer science point of view, but I’d rather it was something like ‘the minimum unit for understanding’.



1] http://www.merriam-webster.com/dictionary/gestalt “a structure, configuration, or pattern of physical, biological, or psychological phenomena so integrated as to constitute a functional unit with properties not derivable by summation of its parts”

Received on Wednesday, 16 November 2016 18:00:16 UTC

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