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Re: pixel densities, text sizing

From: Felix Miata <mrmazda@earthlink.net>
Date: Thu, 08 May 2014 02:50:29 -0400
Message-ID: <536B2935.8020504@earthlink.net>
To: w3c-wai-ig@w3.org
On 2014-05-03 02:06 (GMT+0100) Patrick H. Lauke composed:

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

Actually we weren't. The mention of Retina was an offer of proof of a real 220DPI 
device people could buy and use as opposed to some arbitrary "non-standard setup".

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

And if I had selected the non-Mac 235 DPI M3800 Dell instead?....


> 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.

My screenshots don't purport to address any ability or not of any DE to in any manner 
vary the physical size of a CSS px to match or emulate some specification. That's a 
whole other subject orthogonal to the reasons why I wrote and write in this thread.

I write because using the px unit, among other things:

1-for setting text size wholly and utterly disregards user-determined optimal text 
size as registered by the visitor's UA default size. Translation: disrespect for 
users (aka rude); negative accessibility impact.

2-for setting container size and/or leading can cause an assortment of problems when 
text size is forced by the user to deviate from the stylist's CSS "suggestion" toward 
or reaching user-optimal, including but not limited to: hidden text, overlapping 
text, uncomfortably or inanely short line lengths, and misinterpretation due to 
unexpected text position.

3-is absolutely unnecessary to effectuate the perspectives inherent in any particular 
web page design, unnecessarily reducing accessibility

> 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.

[Addressed by my 2014-05-08 01:11 (GMT-0400) thread post.]

>> 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.

You missed the part about "on average". A Macbook Pro is anything but average. An OS 
or DE may or may not provide a reasonable compensation, if any at all, for display 
pixel densities that deviate modestly or moderately from the standard 96 assumption. 
e.g. on Windows 8 DPI must reach 140 in order for it to scale, and to scale further 
180 must be reached.
http://blogs.msdn.com/b/b8/archive/2012/03/21/scaling-to-different-screens.aspx


....On the 235DPI M3800 Dell, according to that blog URL, Windows would be applying 
180DPI scaling to a 235DPI device, a 23.4% nominal shortfall, a 41.3% shortfall WRT 
real size (a function of squares, it takes only a 41.4% increase in height and width 
to produce twice the px in total. A 1920x1200 screen's px count is 12.5% greater than 
a doubling of the px count of a 1280x800 screen. An em block twice the physical 
*size* of a 16px em block if it could exist would be 22.6275px.).
-- 
"The wise are known for their understanding, and pleasant
words are persuasive." Proverbs 16:21 (New Living Translation)

  Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

Felix Miata  ***  http://fm.no-ip.com/
Received on Thursday, 8 May 2014 06:50:53 UTC

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