From: wdr@world.std.com (William D Ricker)
Newsgroups: comp.fonts
Subject: Point-size origins (Was Re: QUESTION: Why are truetypes w i d e r)
Date: 29 Sep 92 22:48:37 GMT
Article-I.D.: world.BvD3D2.DM3
Organization: The World Public Access UNIX, Brookline, MA


>In article <1992Sep24.210227.10815@shearson.com> dmandl@shearson.com writes:
>>I may be misunderstanding what you're trying to say, but point size
>>is a very precise measurement. ... it's a VERTICAL measurement
  Right so far...

>>the size of the type body (in the old days),
  Still Right...
>>or the total height from the top of the highest
>>ascender to the bottom of the lowest descender.
   No.  In the world of Photo-typesetters and digital fonts, this is
only an approximate lower bound; in the Old days, it was almost always
a firm lower bound, and there was warning on the exception.
   Point-size is the measure of *default* or *minimum* inter-baseline
distance; inter line distance in absense of leading, a/k/a "set
solid".  If you don't know if the text was set solid or leaded, you
can't tell the point-size with a measuring glass unless you know if
the type design includes built-in space betweed adjacent, set-solid
lines.

Exceptions to the Points=Asc-to-desc size rule:
 1.  In metal, their usually a little room between the highest & lowest corners
of the face and the body size, so that the Matrix was completely modlding the
face and not relying on the mold-body to form a vertical side to the printing
face -- since a bevel or beard is desirable for impression and strength.
 2.  If the designer of a face thinks it should always be set leaded, s/he
may choose to include the minimal leading in the design, in which case it
is included in the base point size, and no Cap, lc-ascender, or lc-descender
will get very near the edges.  
 3.  Some faces the Caps are taller than the Ascenders, and others
vice versa.  Vertical sticks on Caps are called Stems, not Ascenders.
Min point size estimate would normally be the height of the font's 
"enveloppe", to borrow from Avionics/Aeronautics.
 4.  Point size of a "Titling Face" may not include descenders; in
which case the Q's tail hangs off the body as a vertical Kern.  Such a
face in metal usually has "Titling" in the name, although sometimes
the fact that only CAPS are available is all the hint given.
  (My metal font of Ray Shaded, cast on a Monotype Display caster, has
"vertical kerns" if you will, hanging the shaded tail of the Q and
some punctuation below the 24pt body, because it has no lower-case.
It might be better described as been 36/24, Thirtysix point type cast
on a 24 point body, since the Cap A is about the height and density of
a Ultrabold 36pt A in many other fonts.  It would be called 36/24 Caps
if a lowercase had been cast on a 36 point body, but since only UC was
ever cut, as UC-only titling, it was standardly issued and refered to
as a 24 point titling -- mucht to the confusion of non-cognoscenti.)
 5.  The Continental Point A/k/a the Didot point (and its Pica Em
equivalent, the Cicero) is just a hair longer.  15 Ciceros == 16
Picas, 15 Didots == 16 Points.  So type which is imported or cast from
imported matrices has been, and still is, cast on the next size larger
body in anglo-american points.  So an 11D/12 or 12D/14 type will look
larger than a similar 12pt font but smaller than a simlar 14pt
font, by about a point of fixed built-in leading that the designer
didn't intend.  What happened when these faces were converted to photo
and digital comp, I don't know.  (I could find out.)  Probably some were
scaled to American sizes proportionally from the european masters, some
copied from the American castings with built-in leading to ease conversion,
and some were probably done both ways at different conversion houses.

Net result: Unless you know it's Adobe Times Roman or whatever and
just want to know what point size & leading options were, you can't
measure the size with a definition and an optical micrometer.  The
defnition is embodied/manifested in the typesetting "hardware", even
if it is software, not the product.

In <5762@dove.nist.gov> gilligan@bldrdoc.gov (Jonathan M. Gilligan) writes:
>I didn't realize that this was supposed to be the definition.  I have
>clearly put too much credence in Knuth's statement that the design
>size is ``a more-or-less arbitrary number that reflects the size of
>type [a font] is intended to blend with'' (METAFONTbook, p. 96).
   I hate to publically disagree with Knuth, as one is almost always
wrong when doing so.  Luckily, I don't have to.  "Coo much credenced"
was very nicely put. The statement quoted^2 above is true only in the
context of Metafonts.  Metafonts (and this definition) are perfectly
adequate for Knuth's purposes but not fully descriptive of all of
typography.  And definitely not conformant to established usage.
   Which is not to condemn heterodoxy, but just to warn that while
the acii markup notations in Knuth's Second Great Work are even more
widely disseminated than his wonderful coinage of mathematical
notations in The First Great Work, Knuth V.I,II,III (And I greatly
appreciate rumors that he intends to publish IV soon!), Metafont has
not been accepted as an encoding for all useful fonts for the future,
and the defintions of font characteristics in Metafont context must be
taken with a large grain of salt when used with fonts outside the
metafont font-generation paradigm.
   This quote (attributed to Knuth in a Metafont context) when applied
to a (non-metafont) Font Designer overstates the arbitrariness of the
design choice; the designer was stating in the old days that you'd
need a Saw, a File, or a Caster with his matrices if you wanted to use
negative leading to set his type closer than he wanted to see it set;
and today, in Photo/digital comp, the designer is either indicating
the opinion of the original metal-head or his own desgin advice as to
what the minimum distance between adjacent baselines should be.
   Also, Pointsize is very poor predictor of blending, except in a
mechanical sense in terms of not-overflowing the same rectangles.
Some faces to blend *in the same line* with 12 point type will need to
be 10/12 or 14/12, due to differences in the way they fill the space.
(The overall leading should fit the body type.)  Harmony & Contrast of
Overall color, shape, style, etc are much more important consid-
erations for blending than body-size.  (For two types to work together,
there must be sufficient harmonies between them to work together and
sufficent contrasts to be easily distinguished.  See Carl Dair's books.)

  [BIBLIOGRAPHY]
  [If one wants to understand usage of typographical terms in the
general milieu, the /Chicago Manual of Style/'s appendix on Typesetting
for Authors is a good capsule presentation of history & terminology;
if one wants the nitty-gritty on how Digital type does, or at least
should, differ and be treated differently from just copies of metal,
see Richard Rubinstein, /Digital Typography/, MIT Press.  (Order by Email
through Quantum Books, quanbook@world.std.com; no relation, we just rent
Email from same node, & I'm a happy walk-in customer; I am an acquaintance of
Rubinstein's, but I liked the book first.)  On type in general, consult
D.B.Updike in a library (out of print), or A(lexander) S.Lawson (who covers
electronic type in his latest revision!).


Bill Ricker, Swamp-Castle Press


-- 
Bill Ricker wdr@world.std.com      "The freedom of the press belongs 
(formerly wdr@wang.com)             to those who own one."
Newsgroups: comp.fonts,gnu.misc.discuss