RE: pixels and points

Ahhh...

Device pixels are easy enough to understand, and tend to be the usual
interpretation amongst adaptation specialists in DIWG. XLS pixels are
approximations to typical displays, but with increasing display
diversity this might cause trouble. CSS pixels are also relative to the
viewing device, and permit reinterpretation if the physical resolution
is considerably different from a reference described as the size of dot
that would produce the same viewing angle as would result from an actual
dot on a 90 dot-per-inch screen when viewed at an "arm's length"
(nominally 28 inches).

So in the case of CSS, the distance from the screen forms part of the
interpretation of the meaning of pixel.

In the case of the starter functions, given that they must replicate the
functionality of Media Queries, the value returned must be in the same
units used by MQ functions. In this case, px should be the stylesheet
variety (CSS). We may need a separate unit for physical pixels, and we
may need to consider the "dpi" issue (as used in 'resolution') because
that refers to physical dots.

Thanks for opening that can of worms :)

---Rotan


[1] http://www.w3.org/TR/css3-mediaqueries/#units

-----Original Message-----
From: public-diselect-editors-request@w3.org
[mailto:public-diselect-editors-request@w3.org] On Behalf Of Chris
Lilley
Sent: 31 May 2006 21:08
To: public-diselect-editors@w3.org
Subject: pixels and points


Hello public-diselect-editors,

In section 9.15.1 Length Units
http://www.w3.org/TR/2005/WD-cselection-20050502/#sec-length-units

I read

  px

    the length is specified in pixels

Please specify whether these are device pixels, px as defined in XSL, px
as defined in CSS, or some other type of pixel.

I also see

  pt

    the length is specified in font points

Please specify whether there are 72.000 to the inch or some other real
number (Didot points, Johnson/American points, etc)

http://en.wikipedia.org/wiki/Point_%28typography%29

I suggest defining this as 72, ie computer DTP points.
    
-- 
 Chris Lilley                    mailto:chris@w3.org
 Interaction Domain Leader
 Co-Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG

Received on Wednesday, 31 May 2006 20:37:52 UTC