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Re: position of baseline relative to em square

From: Nick Nussbaum <nickn@seanet.com>
Date: Wed, 1 Dec 1999 11:24:53 -0800
Message-ID: <002d01bf3c31$bf2c9fa0$6209070a@nickn0>
To: "David Lemon" <typenerd@slip.net>
Cc: <www-font@w3.org>
As long as you're explaining things so lucidly; In Adobe fonts are accented
Upper Case characters
always within the Em Square vertical constraints? Do Pi/Symbol fonts always
fall with in the em square vertical limits?

----- Original Message -----
From: David Lemon <typenerd@slip.net>
To: <www-font@w3.org>
Cc: <erik@netscape.com>
Sent: Wednesday, December 01, 1999 8:54 AM
Subject: Re: position of baseline relative to em square

> At 9:18 PM -0800 11/30/99, Nick Nussbaum wrote:
> > Shouldn't it include extra leading ?
> > I can't check right now because I'm home offline but is the extra
> > considered part of the
> > the baseline to baseline?
> There are two different functions here. The first is the historic one, in
> which the em square is a function of the type size, and the designer fits
> the font into the em square at a proportion appropriate to its use. This
> the reason that most historical designs are somewhat shorter then the em
> height from ascender top to descender bottom. The second is a recommended
> additional leading value (reflecting the fact that most text has something
> around 20% extra leading added in the setting). But this external leading
> is not part of the em square. The em height is equivalent to
> baseline-to-baseline distance when set with no added leading ("solid" in
> metal terminology).
> What I referred to earlier is that Adobe specifies the typographic ascent
> and descent such that their absolute values sum to the em height (thus
> getting the em's position relative to the baseline into the font
> information). We believe this is in line with the original intent of the
> TrueType typographic ascender and descender values, and in the next
> of the OpenType specification we hope to explicitly recommend this
> for all OpenType fonts. Since these values have been rather loosely
> specified to date, other fonts may only approximate this effect. As Greg
> Hitchcock suggested, one could take the sum of the ascent and descent
> values, determine the difference from the em value (zero in Adobe fonts),
> and add half that difference to each to get a pretty good placement of the
> em.
> - David Lemon
Received on Wednesday, 1 December 1999 14:22:43 UTC

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