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

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