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Re: 16px default, SI meter (Re: platform-specific font size issues)

From: Håkon Wium Lie <howcome@w3.org>
Date: Mon, 4 Jan 1999 01:08:24 +0100 (MET)
Message-Id: <199901040008.BAA06122@stovner.sys.sol.no>
To: Todd Fahrner <fahrner@pobox.com>
Cc: www-style@w3.org
Todd Fahrner wrote:

[sorry I'm entering this late]

 >  " If you are looking for a new definition for the reference pixel,
 >  perhaps, like DSSSL and early XSL, CSS lengths could be based on the SI
 >  meter? Or are inches becoming a U.N. recommendation? :-)
 > 
 > By my reading of CSS1, the "real" suggested reference pixel is a degree of
 > visual angle. The conversion to inches (1/90") merely provides an example
 > of what this works out to at arm's length. Wonder if Hakon or Bert can
 > comment.

Yes, the motivation was to establish the pixel unit as a visual angle
instead of tying it up to a certain device/resolution or other things
that might change over time. The CSS1 spec uses a 90dpi example since
that's a close to the average number a 28 inch arm since that's
roughly how long the average arm is. Now, by twisting arms or bying new
machinery, thees numbers can change significantly but the visual angle
shouldn't. 

[In an earlier message Todd wrote]

 > 2. The 1996 CSS1 standard suggests a 1/90" value for a "reference pixel",
 > extrapolated from a visual angle of 0.0227 degrees visual angle at arms
 > nlength. UAs are expected to scale pixels appropriately if the physical
 > resolution is known to vary significantly from this value. A 1/90"
 > reference pixel would suggest a rasterization of 12pt into 15px, rather
 > than 16.

Now you're using the "reference pixel" for something it wasn't designed
to do. It was designed to determine how to interpret a CSS pixel value
(e.g. "10px") into a device-dependent pixel value. It was not designed
to determine how to interpret a non-pixel value (e.g. "12pt") into a
device-dependent pixel value.

-h&kon

H   å   k   o   n      W   i   u   m       L   i   e
howcome@w3.org      http://www.w3.org/people/howcome
World     W      i     d     e       Web  Consortium
Received on Sunday, 3 January 1999 19:08:38 GMT

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