Re: ascender, descender, cap-height and x-height

Todd Fahrner wrote:
> 
> At 5:13 PM -0800 1/27/00, Erik van der Poel wrote:
> >
> >Perhaps my problem is that I believed him. Do you not believe that there
> >exist European fonts with accents *inside* the em?
> 
> I have no cause for doubt.
> 
> Such fonts simply won't play well amid the bread-and-butter faces
> specified on the Web today. In proportion to the seriousness of the
> problems they cause, neither authors nor readers will favor them.

OK, well I'm just going to drop that issue for now. If Kent wants to
defend those fonts, he is of course free to do so.

> I think that the meaning of font size in OS's, in CSS, and in font
> formats is too stable to upset. The gain would not be worth the
> disruption IMO.

I started to feel that way myself this morning.

> otoh, if you wanted to redefine font-size-adjust's
> "aspect value" as the ratio of x-height to bounding box height ...
> that could be interesting. There's no legacy implementation or
> practice to upset.

One thing that bothers me about using the font's bounding box height is
that it is really a reflection of the most extreme glyph(s). From that
point of view, it might be better to use some sort of average or median,
or even just the em, for that matter. I don't really have a good feel
for how important it is to have an "accurate" value in both the
numerator and denominator of the aspect value.

> I understand that ex is not applicable to many scripts. By "analogous
> to ex", I meant only to make the point that all character sets must
> have some minimum required ppem before some critical feature becomes
> indistinct. For u&lc latin, the first casualty is the ex - the
> counters tend to clog below 9px. I'm guessing that CJK requires more
> pixels. Which feature breaks in fewer?

The complicated characters with many strokes will break if you have too
few pixels. On Unix, one of the smaller Japanese fonts is 14px. I've
heard that some Japanese fonts on other platforms can be as small as
12px, if I remember correctly.

> That feature would be
> *analogous* to ex for the purposes of implementing something like
> font-size-adjust.

The font-size-adjust property is defined in terms of an "aspect" value,
which is a ratio between a small thing (ex) and a large thing (em). In
Japanese, there are no small and large things. They are all the same
size, and they are all square, except for minor differences in the ASCII
(Latin) and Hankaku Kana areas, but even those are of the same height as
the square characters.

At some point, it might be nice to consider adding some wording to the
font-size-adjust spec to clarify this issue.

Erik

Received on Friday, 28 January 2000 01:11:13 UTC