User Guide

extra work up front.
Pair kerning, or informally, just “kerning,” is a way of
overriding a character’s spacing in certain circumstances.
To do kerning, you must first have a properly spaced font.
So, in this example, you would pick a width for “T” which
works best for most cases. Since overlapping characters
look pretty ugly and should almost always be avoided, you
will pick a width that fixes “Th” and “TT,” and leaves “To”
a little loose. Once the spacing has been determined, you
then look at all the character combinations which cause
trouble for the spacing value you picked. Typical problem
character pairs involving “T”
are “Ta,” “Te,” “To,” “Tu,” “Tw,” “Ty,” “T,” and so on.
Those character pairs are prime candidates for kerning
pairs. You can create different kerning pairs for each of
those cases, and individually adjust the spacing for each pair.
Here’s how it works: Let’s say the optimum width for “T”
is 825 em units. That means that the “T” is always 825
units wide, no matter what character follows it, except for
the ones we define as kerning pairs. For example, the “T”
in “Ta” could pretend to have a width of 780, so the “a”
gets tucked underneath a bit. For “Te,” we would start with
the same value and modify it, if necessary.
Another way to say it is that in the presence of kerning
pairs, widths of characters can change depending upon what
the next character is (i.e., the widths are contextually
sensitive).
There is an upside to kerning pairs, which we have
discussed, and a downside. Many programs do not support
kerning. There is a rule of thumb to use about kerning and
whether programs do it: typically, if the suggested retail
price of a piece of software is $400 or over, it will support
kerning. Otherwise, it may not. There are exceptions to this
rule of course, but it is usually correct. Programs that do
page layout (Aldus PageMaker, Quark XPress, etc.) almost
always use kerning; the same is true for the higher-end
graphics programs. Some word processors, spreadsheets,
databases, and cheaper graphics programs still do not
support kerning. Anyway, the point is that a font must look
halfway decent without any kerning in it at all, because you
will probably want your font to look good both in your word
processor (without kerning) and in your page layout
Fontographer User's Manual
5: Metrics: Spacing and Kerning Page #6