[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Dvipng] does dvipng include the dpi information in its output?

From: Marc Culler
Subject: Re: [Dvipng] does dvipng include the dpi information in its output?
Date: Mon, 15 Oct 2012 07:44:34 -0500
User-agent: Mutt/1.5.20 (2009-06-14)

On Mon, Oct 15, 2012 at 02:23:27PM +0200, jfbu wrote:

> if a pt (as in your text above) is indeed the absolute measure
> 1/72.27 of an inch then I am more on the side of browsers who
> use points rather than pixels! if that means that they take
> into accoung the device dpi in order to display a 12pt font
> as really a 12 true points on screen, with whatever pixels
> this requires!

If only it were that simple.  For *typesetting* a point is 1/72.27
inches, but on the web a point is defined by the CSS specification
to be 1/72 inches.  To convert points to pixels, according to CSS,
a browser is supposed to assume that the size of a pixel is equal
to the size of a "reference pixel".  The definition of a 
reference pixel is 

   "The reference pixel is the visual angle of one pixel on a device
   with a pixel density of 96dpi and a distance from the reader of an
   arm's length. For a nominal arm's length of 28 inches, the visual
   angle is therefore about 0.0213 degrees. For reading at arm's
   length, 1px thus corresponds to about 0.26 mm (1/96 inch)."

[ http://www.w3.org/TR/css3-values/#absolute-lengths ]

But of course the size of a reference pixel is configurable by the
user.  The Ctrl-+ and Ctrl-- keys change the size of a reference
pixel, and the ability to do that is a key component of web
accessibility.  The bottom line is that browsers can display 12 point
type at pretty much any size.  Certainly, as a web designer, you
cannot assume anything about the size at which a 12 point font will
be rendered on a screen.

- Marc

reply via email to

[Prev in Thread] Current Thread [Next in Thread]