RE: CFC: Target Size and Target Size (no exception) SC

[Steve wrote]   If you're talking about color inversion, that has mathematically zero effect on contrast ratio.
[Jonathan wrote] This absolutely does.  Inverted colors change the contrast.  
[Steve] Again I should amend to say "minimal" and not "zero" because the conversion from 24-bit RGB space to SRGB is not linear, but that's the only reason there's a small effect on contrast ratio.

Steve, inverting the color changes the contrast of a color -- this is proven mathematically.  For example, take the color white on a blue background
#fffff on #0A3B70
This has a contrast of 11.22:1

Invert the color values and you get

#00000 on #F5C48F
This has a contrast of 13.8:1

Jonathan

Jonathan Avila
Chief Accessibility Officer
SSB BART Group 
jon.avila@ssbbartgroup.com
703.637.8957 (Office)

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-----Original Message-----
From: Repsher, Stephen J [mailto:stephen.j.repsher@boeing.com] 
Sent: Wednesday, May 24, 2017 10:30 AM
To: Jonathan Avila; Patrick H. Lauke; w3c-wai-gl@w3.org
Subject: RE: CFC: Target Size and Target Size (no exception) SC



Steve


-----Original Message-----
From: Jonathan Avila [mailto:jon.avila@ssbbartgroup.com]
Sent: Wednesday, May 24, 2017 9:19 AM
To: Repsher, Stephen J <stephen.j.repsher@boeing.com>; Patrick H. Lauke <redux@splintered.co.uk>; w3c-wai-gl@w3.org
Subject: RE: CFC: Target Size and Target Size (no exception) SC

> Let's not get carried away here.  If you're talking about OS high contrast modes, those have no effect on web content.

They certainly do with user agents that support taking the high contrast colors and applying them to the page based on the user's preference.  This is support in Firefox and IE in Windows.
[Steve] True and I should amend my statement - thanks.  I did not want to go into a discussion of how effective those actually are or how well supported they are.

>   If you're talking about color inversion, that has mathematically zero effect on contrast ratio.

This absolutely does.  Inverted colors change the contrast.  
[Steve] Again I should amend to say "minimal" and not "zero" because the conversion from 24-bit RGB space to SRGB is not linear, but that's the only reason there's a small effect on contrast ratio.

Jonathan


Jonathan Avila
Chief Accessibility Officer
SSB BART Group
jon.avila@ssbbartgroup.com
703.637.8957 (Office)
Visit us online: Website | Twitter | Facebook | LinkedIn | Blog Download our CSUN Presentations Here!

The information contained in this transmission may be attorney privileged and/or confidential information intended for the use of the individual or entity named above. If the reader of this message is not the intended recipient, you are hereby notified that any use, dissemination, distribution or copying of this communication is strictly prohibited.


-----Original Message-----
From: Repsher, Stephen J [mailto:stephen.j.repsher@boeing.com]
Sent: Wednesday, May 24, 2017 9:11 AM
To: Patrick H. Lauke; w3c-wai-gl@w3.org
Subject: RE: CFC: Target Size and Target Size (no exception) SC

> Why do websites need to define a specific minimum color contrast when users can just use high contrast mode on their device?
Let's not get carried away here.  If you're talking about OS high contrast modes, those have no effect on web content.  If you're talking about color inversion, that has mathematically zero effect on contrast ratio.

Steve

-----Original Message-----
From: Patrick H. Lauke [mailto:redux@splintered.co.uk]
Sent: Wednesday, May 24, 2017 5:22 AM
To: w3c-wai-gl@w3.org
Subject: Re: CFC: Target Size and Target Size (no exception) SC

On 24/05/2017 02:58, Gregg C Vanderheiden wrote:
> I still continue to have concerns about this.     40px is a non-defined 
> size.   on ever device it is a different size 
 > — yet we are saying it
 > MUST be this big or larger —  when  THIS   is some arbitrary size on
 > different screens.
 >

Note that it's not completely arbitrary, just the best that can currently be defined.
On devices/UAs where a CSS pixel approximately matches the definition of the reference pixel https://www.w3.org/TR/css3-values/#reference-pixel a size defined in CSS pixels shakes out to roughly (with varying degrees of "rough") the same size at the same viewing/use distance.

Indeed, on mobile/touch devices there's certainly variance, but a size defined in CSS pixels (when the ideal viewport is set on the page using the appropriate meta element) comes to roughly the same size as rendered on the screen. (regardless of whether it's a high-dpi/"retina" display or not, since we're talking CSS pixels and not actual physical pixels).

See
https://www.w3.org/WAI/GL/mobile-a11y-tf/wiki/Summary_of_Research_on_Touch/Pointer_Target_Size#Comparison_of_web_content_sized_in_px_and_physical_size_of_rendered_content_on_common_device_screens


[...]
> Finally — why do controls need to be large for everyone when a person 
> who needs them to be larger can zoom to make them larger — as large as 
> they need them to be.

Why do websites need to define a specific minimum color contrast when users can just use high contrast mode on their device?

Zooming (in most/all user agents on phone/tablet devices) leads to horizontal and vertical scrolling. Yes, a user can zoom to make targets more easily "tap-able", but at the expense of then having to scroll in both directions around the page.

Having said all that, I'm still personally leaning more towards turning this into a best practice piece of advice (in Silver), rather than a hard SC in WCAG 2.1.

P
--
Patrick H. Lauke

www.splintered.co.uk | https://github.com/patrickhlauke http://flickr.com/photos/redux/ | http://redux.deviantart.com

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Received on Friday, 26 May 2017 14:05:31 UTC