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Re: [css3-values] New WD for Values & Units

From: David Woolley <david@djwhome.demon.co.uk>
Date: Sun, 31 Jul 2005 10:08:33 +0100 (BST)
Message-Id: <200507310908.j6V98Xd00479@djwhome.demon.co.uk>
To: www-style@w3.org

> I disagree. To give an example to illustrate, on e.g. an MSX computer, 
> there are screenmodes which have pixels which are not angular at all. 

Pixels are over-used because designers haven't bought in to the 
device independence idea and still design for their own graphics
card, or at least an "IBM" PC with the most common resolution of the
day, operated full screen.

However, given there is no current viable (i.e. fully integrated and
doesn't require a third party plugin) way of handling vector graphics
and bandwidth is important, so greatly oversampling bitmaps isn't 
practical, engineering constraints mean that most, heavily styled, 
pages look bad if device pixels aren't an integral multiple of the
bitmap image pixels.

> Among the possible screen resolutions are 512 x 212 and 256 x 424 (on a 
> regular 4:3 TV). These will result in non-square pixels (they are twice 

Whilst people rely on bitmap images for ornamentation, such resolutions
are always going to be a problem because they are not high enough to 
simply oversample the image.  Such devices are also always going to
be problematic with photographs scanned using square pixels or from
digital cameras.

PDF avoids a pixels unit by having proper vector graphics and by typically
having different versions of the document for screen use/home printing and
professional printing, with different resolutions of bitmapped image.

> Also, pixels aren’t device pixels anyway - when the dots per inch are 
> too high, their size is a multiple of device pixels.

As I understand it, this is the real reason for using the angular unit
abstraction.  That means that pixels sizes need to round to an integral
number of device pixels, at least for square pixel devices, which can 
result in much more than 10% tolerances in the angle.  If a pure 
angular unit were introduce and pixels made device pixels, most authors
would ignore the angular unit and use the device pixels.  In my
experience, most commercial pages are unprintable, as they tend to
overflow the paper, but I imagine that browser developers would ignore
any attempt to use a true device pixel on printers.

> they are used on a VGA, NTSC or PAL display (while they are only truly 
> square on - most - VGA displays).
> 
And all common digital cameras.  Scanner pixels, except for fax scanners,
are either square or 2:1 rectangular (high resolution fax pixels are
not quite square, but often approximated as such by computers).
Received on Sunday, 31 July 2005 09:08:43 GMT

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