[html5] Absolute Pixels in HTML 5

Ian Hickson ian at hixie.ch
Thu Jun 11 12:17:50 PDT 2009

On Mon, 25 May 2009, Sean B. Palmer wrote:
> HTML 5 currently says that img/@width and so forth use CSS 2.1 pixel 
> values. Pixel values in CSS 2.1 are of course a relative rather than an 
> absolute unit. In other words, CSS px is a non-linear alias for radians; 
> 675.522px, for example, is a quarter of a radian.
> But non-vector image formats like JPG and PNG have discrete pixels, and 
> screens have pixel displays with certain ppi values. So has anybody 
> looked at whether browsers actually implement px as a relative unit? And 
> how do they render images? I'm presuming that they don't resample to fit 
> the relative measurement.

It's hard to say today because monitors are all assumed to be 96dpi. The 
idea of using CSS pixels everywhere is to make the spec be ready for when 
screens have higher resolutions.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
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