Re: Color contrast principle

+1

On Thu, Jan 17, 2019 at 4:57 AM Alastair Campbell <acampbell@nomensa.com>
wrote:

> David wrote:
>
> > If the grey outline is merged with the dark blue background wouldn't the
> contrast be between the input and the dark gray background.
>
>
>
> As we’re dealing with luminance, most contrasting colour combinations are
> a dark colour vs a light colour. A colour in the middle is very likely to
> fall into the dark or light side, so be ‘subsumed’ into one side or the
> other. (Insert star-wars joke here.)
>
>
>
> it is possible to have three contrasting colours, light, middle and dark,
> and if that is the case then great, the silver could contrast with both and
> could be taken as the measure.
>
>
>
> What we’re saying is that if that 3-way contrast isn’t the case, **and**
> it does not impact understanding the component, then you can consider it
> part of the closest match (light/dark).
>
>
>
> Logically, if the inner and outer colour do contrast, then the middle
> colour either will either:
>
>    - contrast with both (unlikely but good), or
>    - contrast with one side (be subsumed into the non-contrasting side)
>    - contrast with neither (be ignored).
>
>
>
> That last one might look worrying, but could be considered to essentially
> be like a gradient. If that is thick enough to interfere with the
> comprehension of the control, it would be an issue. I’m struggling to think
> of an example of that though. If the outer and inner colours contrast
> enough, that should be ok. If it is particularly thick (e.g. a border
> between maps segments), it is likely to be considered its own graphical
> object.
>
>
>
>
>
> JF wrote:
>
> > I think the word we may be searching for is subsume
>
>
>
> Works for me, that would make it:
>
>
>
> If components use several colors, any color which does not interfere with
> identifying the component can be ignored for the purpose of measuring
> contrast ratio. For example, a 3D drop-shadow on an input, or a dark border
> line between contrasting [*backgrounds is considered to be subsumed into
> the color closest in brightness (luminance)].*
>
>
>
> The following example shows an input that has a light background on the
> inside and a dark background around it. The input also has a dark grey
> border which [*is considered to be subsumed] *into the dark background.
> The border does not interfere with identifying the component, so the
> contrast ratio is taken between the white background and dark blue
> background.
>
>
>
>
>
> Having agreed the last update to this understanding doc, we’ll publish
> that first and this change will go into the next updates for non-text
> contrast, I’ll start a new branch/PR for it.
>
>
>
> -Alastair
>


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