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pixel densities, text sizing (was Re: Accessible college websites)

From: Patrick H. Lauke <redux@splintered.co.uk>
Date: Thu, 08 May 2014 02:06:44 +0100
Message-ID: <536AD8A4.9030609@splintered.co.uk>
To: w3c-wai-ig@w3.org
On 08/05/2014 01:05, Felix Miata wrote:
> Maybe something more familiar will help you understand:
> http://fm.no-ip.com/SS/SC/sc-patlau1405-220.png image
> http://fm.no-ip.com/Tmp/sc-patlau1405.html setup
>
> Same viewing instructions apply: either view in a viewer with the 1"
> image 1" wide, or adjust viewing distance according to the formula. This
> though is from a different "non-standard" setup. Instead of the 144DPI
> density of the images in my previous thread post, this has the 220DPI
> density of a high dollar Macbook Retina, which makes its
> http://redux.deviantart.com/ subject's 10px P text true scribble that
> even those with the best of vision, plus a magnifier, would have a tough
> time reading at all, much less with any semblance of comfort.

Well, as we're talking retina versus non-retina...have a look at this shot

http://i.imgur.com/q76abmy.jpg

MacBook Pro with Retina display on the left, MacBook Pro with non-Retina 
on the right. At same viewing distance all the text looks exactly the 
same size...because the OS compensates for the higher pixel density. So 
your example screenshots don't actually reflect the reality in this 
particular case.

In fact, this is consistent with the reference px definition: at the 
same viewing distance, the CSS reference pixel dimension needs to remain 
the same, regardless of actual physical device pixels. If I follow the 
rationale of your viewing instructions, you seem to imply that a viewer 
should adapt their viewing distance in order to keep the ratio of the 
dimension of a *physical* pixel and the viewing distance constant, 
whereas the CSS px reference definition is based on the ratio of the 
dimension of a *CSS* pixel and the viewing distance. For the same 
type/class of device, with same screen size, I should not adjust my 
viewing distance at all...it's the OS that needs to adjust its mapping 
of CSS pixels to physical pixels.

> Have you never noticed that as the price of PC
> equipment goes up, that pixel density, on average, goes up too, meaning
> everything shrinks

No it doesn't, see above.

> Stylists

Ah, I was waiting for that classic term to crop up.

P
-- 
Patrick H. Lauke

www.splintered.co.uk | https://github.com/patrickhlauke
http://flickr.com/photos/redux/ | http://redux.deviantart.com
twitter: @patrick_h_lauke | skype: patrick_h_lauke
Received on Thursday, 8 May 2014 01:07:08 UTC

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