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Re: Graphics contrast

From: Jim Allan <jimallan@tsbvi.edu>
Date: Wed, 16 Nov 2016 11:42:26 -0600
Message-ID: <CA+=z1WnzjC8Kfxe8Yiiq2ApRNyiJuXr3o-DL-QEcdFvyZvbgCQ@mail.gmail.com>
To: Glenda Sims <glenda.sims@deque.com>
Cc: Alastair Campbell <acampbell@nomensa.com>, public-low-vision-a11y-tf <public-low-vision-a11y-tf@w3.org>
On Fri, Nov 11, 2016 at 8:32 AM, Glenda Sims <glenda.sims@deque.com> wrote:

> Alastair,
> I think you and I are thinking the same way.  The reason I'm not
> comfortable just saying "adjacent elements" is...I think it will be
> problematic to objectively measure.  Let's imagine a trashcan icon that is
> being used as an interactive element. Here is a simple example from my
> gmail account: [image: Inline image 1]
> In this case, the primary color of the trashcan is dark grey (#6E6E6E) and
> the primary color of the background is light grey (#F4F4F4).  Ignoring the
> anti-aliasing bits around the end of the trashcan...I grab a pixel of the
> dark grey to compare against a pixel of the light grey....and smile,
> because it is 4.6 to 1.
> BUT...what if the trashcan was rainbow striped diagonally, the lid was
> light purple, the background color was the same light grey  (#F4F4F4) as
> the previous example.
> [image: Inline image 4]
> For testing purposes...let's just focus on the lid...you would look at the
> light purple lid, in your mind, draw a "need to test the background color"
> 3px perimeter around the edge of the lid.  Your brain then says...oh, that
> is just one color in that 3px perimeter around the edge of the lid...so now
> I'll compare the light purple: #CBCBFE to the light grey #F4F4F4...see it
> is only 1.4 to 1, and say, that lid fails.

​agree, lid fails

> But if I had to do this with the trash can body...I would have to compare
> each stripe of the trashcan against the 3 px surrounding area just outside
> the edge of that color of the trashcan.
> So...there is NO requirement for borders on anything.  BUT...for testing
> purposes...we are going to look at the immediate 3 pixels perimeter.

​This is a poor example. nothing in the body of the trashcan passes. ​

​for argument, lets say the red stripes passed but nothing else does. I
think the icon fails.
if the trashcan has a 4.5:1 border with background only, I think the icon

> glenda sims    |   team a11y lead   |    deque.com    |    512.963.3773
> *web for everyone. web on everything.* -  w3 goals
> On Thu, Nov 10, 2016 at 5:03 PM, Alastair Campbell <acampbell@nomensa.com>
> wrote:
>> Hi Everyone,
>> I was reading through the minutes, and considering the term "immediate
>> surrounding background" for both contrast SCs.
>> I think what we're actually trying to say is: "adjacent elements", and in
>> the definition of that include the background as the obvious adjacent
>> element.
>> I.e. it doesn't matter if it is a background or another part of the same
>> graphic, it is what is next to it that counts.
>> That means we aren't asking for borders specifically (which seems
>> implied), there are several techniques that can apply, such as breaking up
>> a slices of pie chart with gaps in between, or a border, or just having
>> contrasting colours.
>> Therefore the graphics contrast SC would start:
>> "The visual presentation of important information in graphical elements
>> has a contrast ratio of at least 4.5:1 against the adjacent elements,
>> except for the following:"
>> Perhaps in the Interactive Element Contrast SC the term background is
>> more applicable because we aren't expecting them to be next to the elements
>> (apart from interactive graphics?)
>> -Alastair

Jim Allan, Accessibility Coordinator
Texas School for the Blind and Visually Impaired
1100 W. 45th St., Austin, Texas 78756
voice 512.206.9315    fax: 512.206.9264  http://www.tsbvi.edu/
"We shape our tools and thereafter our tools shape us." McLuhan, 1964

(image/png attachment: Screen_Shot_2016-11-11_at_8.09.50_AM.png)

(image/png attachment: rainbow_stripe_trashcan_with_light_purple_lid.png)

Received on Wednesday, 16 November 2016 17:43:02 UTC

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