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Re: [css3-values][css3-mediaqueries] resolution in dpi / dppx

From: Simon Sapin <simon.sapin@kozea.fr>
Date: Mon, 28 Jan 2013 20:20:09 +0100
Message-ID: <5106CF69.2040304@kozea.fr>
To: François REMY <francois.remy.dev@outlook.com>
CC: "www-style@w3.org" <www-style@w3.org>
Le 28/01/2013 20:00, François REMY a écrit :
>> For instance, if we say the viewing distance is about half an arms
>> length then the size of a reference pixel would be about 1/128
>> physical inches. Given 312 device pixels per physical inch, this
>> gives 312/128 = 2.4375 device pixels per reference pixel.
> Thanks for the clarification. Is there an online calculator that
> gives the optimal size of a pixel (or the DPI) given the viewing
> distance?

The reference pixel is a visual angle (of about 0.0213 degrees) that 
projects to 1/96 inch at a distance of 28 inches. So at a viewing 
distance D, the reference pixel is (1/96) * D / 28 = D/2688.

http://dev.w3.org/csswg/css3-values/#absolute-lengths

Of course real devices pick some approximation of that for their actual 
CSS pixels, and the actual viewing distance is often unknown and variable.

-- 
Simon Sapin
Received on Monday, 28 January 2013 19:20:33 GMT

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