A |
-
Advance Width
-
The distance between the start of this character and the start of the next
character. Sometimes called the character's width.
-
Ascender
-
A stem on a lower case letter which extends above the x-height. "l" has an
ascender.
See also X-height,
Cap-height, Descender,
Overshoot, Baseline
-
Anchor Class
-
Used to specify mark-to-base and cursive GPOS subtables. See
overview.
-
Ascent
-
In traditional typography the ascent of a font was the distance from the
top of a block of type to the baseline.
Its precise meaning in modern typograph seems to vary with different definers.
-
ATSUI
-
Apple's advanced typographical system
|
B |
-
Baseline
-
The baseline is the horizontal line on which the (latin, greek, cyrillic)
letters sit. The baseline will probably be in a different place for different
scripts. In Indic scripts most letters descend below the baseline. In CJK
scripts there is also a vertical baseline usually in the middle of the
character.
See also X-height,
Cap-height, Ascender,
Descender, Overshoot
-
Bézier curve or Bézier splines
-
Bézier curves are described in detail in the
Bézier section of the main manual.
-
Black letter
-
Any of various type families based on medieval handwriting.
See also gothic.
-
BMP (Basic Multilingual Plane)
-
The first 65536 code points of Unicode. These contain most of the ordinary
characters in the world.
-
Bold
-
A common font style. The stems of the characters are
wider than in the normal font, given the letters a darker impression.
|
C |
-
Cap-height
-
The height of a capital letter above the baseline (with a flat top like "I"
as opposed to one with a curved to like "O").
See also X-height, Ascender,
Descender, Overshoot,
Baseline
-
CFF
-
Compact Font Format used within OpenType
postscript fonts.
-
Character
-
A character is a Platonic ideal reified into at least one
glyph.
-
Character set
-
A character set is an unordered set of characters
-
CID
-
In some CJK
PostScript fonts the glyphs are not named but are
refered to by a CID number.
-
CID-keyed font
-
A PostScript font in which the glyphs
-
CJK
-
Chinese, Japanese, Korean. These three languages require fonts with a huge
number of characters. All three share a writing system based on Chinese
ideographs (though they have undergone seperate evolution in each country,
indeed mainland Chinese fonts are different from those used in Taiwan and
Hong Kong).
Japanese and Korean also have phonetic syllabaries. The Japanese have two
syllabaries, hiragona and katakana which have about 60 syllables. The Koreans
have one syllabary, hangul with tens of thousands of syllables.
-
CJKV
-
Chinese, Japanese, Korean, Vietnamese. These four languages require fonts
with a huge number of characters.
-
Condensed
-
A condensed font is one where the space between the stems of the characters,
and the distance between characters themselves has been reduced.
|
D |
-
Descender
-
A stem on a lower case letter which extends below the baseline. "p" has a
descender.
See also X-height,
Cap-height, Ascender,
Overshoot, Baseline
-
Descent
-
In traditional typography the descent of a font was the distance from the
bottom of a block of type to the baseline.
Its precise meaning in modern typograph seems to vary with different definers.
-
Didot point
-
The European point. 62 2/3
points per 23.566mm ( 2.66pt/mm or 67.54pt/inch )
|
E |
-
em
-
A linear unit equal to the point size of the font. In a 10 point font, the
em will be 10 points. An em-space is white-space that is as wide as the point
size. An em-dash is a horizontal bar that is as wide as the point size.
An em-square is a square one em to each side. In traditional typograph (when
each letter was cast in metal) the glyph had to be drawn within the em-square.
-
em unit
-
In a scalable font the "em" is subdivided into units. In a postscript font
there are usually 1000 units to the em. In a TrueType font there might be
512, 1024 or 2048 units to the em. In an Ikarus font there are 15,000 units.
PfaEdit uses these units as the basis of its coordinate system.
-
en
-
One half of an "em"
-
Encoding
-
An encoding is a mapping from a set of bytes onto a
character set. It is what determines
which byte sequence represents which character. The words "encoding" and
"character set" are often used synonymously. The specification for ASCII
specifies both a character set and an encoding. But CJK character sets often
have multiple encodings for the character set (end multiple character sets
for some encodings).
-
Even-Odd Fill rule
-
To determine if a pixel should be
filled using this rule,
draw a line from the pixel to infinity (in any direction) then count the
number of times contours cross this line. If that number is odd then fill
the point, if it is even then do not fill the point. This method is used
by postscript rasterizers after level 2.0 of PostScript. See Also
Non-Zero Winding Number Fill.
-
Extended
-
An extended font is one where the space between the stems of the characters,
and the distance between characters themselves has been increased.
|
F |
-
Font
-
A collection of glyphs, generally with at least one
glyph associated with each character in the font's
character set, often with an encoding.
A font contains much of the information needed to turn a sequence of bytes
into a set of pictures representing the characters specified by those bytes.
In traditional typesetting a font was a collection of little blocks of metal
each with a graven image of a letter on it. Traditionally there was a different
font for each point-size.
-
Font Family, or just Family
-
A collection of related fonts. Often including plain, italic
and bold styles.
-
FreeType
-
A library for rasterizing fonts. Used extensively in PfaEdit to understand
the behavior of truetype fonts.
-
Fractur
-
The old black letter writing style used in Germany up until the end of world
war II.
See also gothic.
|
G |
-
Glyph
-
A glyph is an image, often asociated with one or several
characters. So the glyph used to draw "f" is associated
with the character f, while the glyph for the "fi" ligature is associated
with both f and i. In simple latin fonts the association is often one to
one (there is exactly one glyph for each character), while in more complex
fonts or scripts there may be several glyphs per character (In renaissance
printing the letter "s" had two glyphs associated with it, one, the long-s,
was used initially and medially, the other, the short-s, was used only at
the end of words). And in the ligatures one glyph is associated with two
or more characters.
Fonts are collections of glyphs with some form of mapping
from character to glyph.
-
Grid Fitting
-
Before TrueType glyphs are rasterized they go through a process called
grid fitting where a tiny program
(associated with each glyph) is run which moves the points on the glyph's
outlines around until they fit the pixel grid better.
-
Gothic
-
The German monks at the time of Gutenburg used a black-letter writing style,
and he copied their handwriting in his typefaces for printing. Italian type
designers (after printing spread south) sneered at the style, prefering the
type designs left by the romans. As a term of contempt they used the word
gothic, the style of the goths who helped destroy the roman empire.
-
Grotesque
-
See also sans-serif.
|
H |
-
Hints
-
These are described in detail in the main
manual. They help the rasterizer to draw a glyph
well at small pointsizes.
|
I |
-
Italic
-
A slanted style of a font, generally used for emphasis.
Italic differs from Oblique in that the transformation
from the plain to the slanted form involves more than just skewing the
letterforms. Generally the lower-case a changes to a, the serifs on
lower-case letters like i (i) change, and the font generally gains
a freer look to it.
|
J |
-
-
|
K |
-
Kerning
-
When the default spacing between two characters is inapproriate the font
may include extra information to indicate that when a given character (say
"T") is followed by another character (say "o") then the advance width of
the "T" should be adjusted by a certain amount to make for a more pleasing
display.
-
Kern pair
-
A pair of characters for which kerning information
has been specified.
|
L |
-
Left
side bearing
-
The horizontal distance from a character's origin to its leftmost extent.
This may be negative or positive.
-
Lemur
-
A monotypic genus
of prosimian primates, now found only on Madagascar but formally (about 50
million years ago) members of this family were much more wide spread.
-
Ligature
-
A single glyph which is composed of two adjacent characters. A common example
in the latin script is the "fi" ligature
which has a nicer
feel to it than the
sequence .
-
LGC
-
Latin, Greek, Cyrillic. These three alphabets have evolved side by side over
the last few thousand years. The letter forms are very similar (and some
letters are shared). Many concepts such as "lower case", "italic" are applicable
to these three alphabets and not to any others.
|
M |
-
Monospace
-
A font in which all characters have the same advance width. These are sometimes
called typewriter fonts.
|
N |
-
Non-Zero Winding Number Fill rule
-
To determine if a pixel should be filled
using this rule draw a line from here to infinity (in any direction)
and count the number of times contours cross this line. If the contour crosses
the line in a clockwise direction add 1, of the contour crosses in a counter
clockwise direction subtract one. If the result is non-zero then fill the
pixel. If it is zero leave it blank. This method is used by truetype and
older (before version 2) postscript rasterizers.
See Also Even-Odd Fill Rule
|
O |
-
OpenType
-
A type of font. It is an attempt to merge postscript and truetype fonts into
one specification.
An opentype font may contain either a truetype or a postscript font inside
it.
It contains many of the same data tables for information like encodings that
were present in truetype fonts. It also can contain additional information
such as positional glyph selection (needed for arabic), ligatures, etc.
-
OpenType Tables
-
Each opentype font contains a collection of tables each of which contains
a certain kind of information. See here for
the tables used by PfaEdit.
-
Oblique
-
A slanted style of a font, generally used for emphasis.
Oblique differs from Italic in that the transformation
from the plain to the slanted form involves just skewing the letterforms.
-
Overshoot
-
In order for the curved shape of the "O" to appear to be the same height
as the flat top of the "I" it tends to "overshoot" the cap-height (or x-height,
or undershoot the baseline) by about 3% of the cap-height (or x-height).
For a triangular shape (such as "A") the overshoot is even greater, perhaps
5%.
These guidelines are based on the way the eye works and the optical illusions
it generates and are taken from Peter Karow's Digital Formats for
Typefaces, p. 26).
See also X-height,
Cap-height, Ascender,
Descender, Baseline
|
P |
-
Panose
-
A system for describing fonts. See AGFA's
PANOSE classification
metrics guide and MicroSoft's
PANOSE
classification in Windows.
-
Pica point
-
The Anglo-American point. With 72.27 points per inch
( 2.85pt /mm ).
-
Point
-
A point is a unit of measurement. There were two different definitions for
"point" in common usage before the advent of computers. The one in use in
the Anglo-Saxon printing world was the "pica point" with 72.27 points per
inch ( 2.85pt /mm ), while the one used in Europe was the didot point with
62 2/3 points per 23.566mm ( 2.66pt/mm or 67.54pt/inch
).
These two points were so arranged that text at a given point-size would have
approximately the same cap-height in both systems,
the didot point would have extra white-space above the capitals to contain
the accents present in most non-English Latin based scripts.
This has the interesting side effect that a font designed for European usage
should have a smaller proportion of the vertical em given over to the text
body. I believe that computer fonts tend to ignore this, so presumably european
printers now set with more leading.
As far as I can tell, computers tend to work in pica points (but this may
be because I am in the US).
-
Point Size
-
In traditional typography a 10pt font was one where the block of metal for
each character was 10 points high.
-
PostScript
-
PostScript is a page-layout language used by many printers. The language
contains the specifications of several different font formats. The main manual
has a section describing how PostScript differs
from TrueType.
-
Type 1 -- This is the old standard for PostScript fonts. Such a font generally
has the extension .pfb (or .pfa). A type 1 font is limitted to a one byte
encoding (ie. only 256 characters may be encoded).
-
Type 2 -- This is the format used within OpenType
fonts. It is almost the same as Type 1, but has a few extensions and a more
compact format.
-
Type 3 -- This format allows full postscript within the font, but it means
that no hints are allowed, so these fonts will not look
as nice at small point-sizes. Also most rasterizers are incapable of dealing
with them. A type 0 font is limitted to a one byte encoding (ie. only 256
characters may be encoded).
-
Type 0 -- This format is used for collecting many sub-fonts (of Type 1 or
Type 3) into one big font, and was used for CJK or Unicode fonts.
-
Type 42 -- A TrueType font wrapped up in PostScript.
Sort of the opposite from OpenType.
-
CID -- This format is used for CJK fonts with large numbers of glyphs.
|
Q |
-
-
|
R |
-
Reference
-
A reference is a way of storing the
outlines of one glyph in another (for example in accented characters).
-
Right
side bearing
-
The horizontal distance from a character's rightmost extent to the character's
advance width. This may be positive or negative.
|
S |
-
Sans Serif
-
See the section on serifs.
-
Script
-
A script is a character set and associated
rules for putting letters together. Latin, arabic, katakana and hanja are
all scripts.
-
Serif
latin
greek
cyrillic |
 |
 |
a serif |
sans serif |
hebrew |
 |
 |
bet serif |
sans serif |
-
Back two thousand years ago when the Romans were carving their letters on
stone monuments, they discovered that they could reduce the chance of the
stone cracking by adding fine lines at the terminations of the main stems
of a character.
These fine lines were called serifs, and came to have an esthetic appeal
of their own. Early type designers added them to their fonts for esthetic
rather than functional reasons.
At the end of the nineteenth and beginning of the twentieth, type-designers
started designing fonts without serifs. These were initialially called grotesques
because their form appeared so strange, they are now generally called sans-serif.
Other writing systems (Hebrew for one) have their own serifs. Hebrew serifs
are rather different from latin (cyrillic, greek) serifs and I don't know
their history. Hebrew serifs only occur at the top of a character
I would welcome examples from other scripts of serifed and sans-serifed
characters.
-
Spline
-
A curved line segment. See the section in the
manual on splines. The splines used in PfaEdit are all third order
Bézier splines.
-
Style
-
There are various conventional varients of a font. In probably any writing
system the thickness of the stems of the characters may be varied, this is
called the weight of a font. Common weights are normal
and bold.
In LGC alphabets an italic (or
oblique) style has arisen and is used for emphasis.
Fonts are often compressed into a condensed style,
or expanded out into an extended style.
Various other styles are in occasional use: underline, overstrike, outline,
shadow.
-
Syllabary
-
A syllabary is a phonetic writing system like an alphabet. Unlike an alphabet
the sound-unit which is written is a syllable rather than a letter. In Japanese
KataKana the sound "ka" is represented by one glyph. Syllabaries tend to
be bigger than alphabets (KataKana requires about 60 different characters,
while the Korean Hangul requires tens of thousands).
|
T |
-
True Type
-
A type of font invented by Apple and shared with MicroSoft. It specifies
outlines with 2 degree Bézier curves, contains
inovative hinting controls, and an expandable series of tables for containing
whatever additional information is deemed imported to the font.
Apple and Adobe/MicroSoft have expanded these tables in different ways, although
attempting to achieve the same effect.
-
TrueType Tables
-
Each truetype font contains a collection of tables each of which contains
a certain kind of information. See here for
the tables used by PfaEdit.
-
Type 1
-
A type of PostScript font which see.
-
Type 2
-
A type of PostScript font, used within
OpenType font wrappers.
-
Type 3
-
A very general type of PostScript font, which see.
-
Type 0
-
A type of PostScript font, which see.
-
Typewriter
-
See Monospace.
|
U |
-
Unicode
-
An encoding character set/encoding which tries to contain all the characters
used in the world. See the Unicode
consortium.
More info.
|
V |
-
-
|
W |
-
Weight
-
The weight of a font is how thick (dark) the stems of the characters are.
Traditionally weight is named, but recently numbers have been applied to
weights.
Thin |
100 |
Extra-Light |
200 |
Light |
300 |
Normal |
400 |
Medium |
500 |
Demi-Bold |
600 |
Bold |
700 |
Heavy |
800 |
Black |
900 |
Nord |
|
Ultra |
|
-
Width
-
This is a slightly ambiguous term and is sometimes used to mean the
advance width (the distance from the start of
this character to the start of the next character), and sometimes used to
mean the distance from the left side bearing to the right side bearing.
|
X |
-
X-height
-
The height of a lower case letter above the base line (with a flat top like
"x" or "z" or "v" as opposed to one with a curved top like "o" or one with
an ascender like "l") .
See also Cap-height,
Ascender, Descender,
Overshoot, Baseline
|
Y |
-
-
|
Z |
-
-
|