User Guide

Hinting
483
Alignment Zones
Alignment zones are typically used to perform a process known as
overshoot suppression:
Rounded characters and characters with sharp ends usually are created a
little bit larger than “flat characters”:
Notice that the top and bottom of the O extend just a little beyond the top
and bottom of the H. This is called overshoot. It is necessary to compensate
for a visual effect that makes rounded characters look slightly smaller.
Usually the overshoot height is set to 3-4% of character height. However, at
small PPM size, this value may be rounded to one pixel.
When the PPM is small, one pixel may be 15% of the character height or
even more. Here’s how it happens:
Assume that the topmost position of the H character is 700 units and the top position of the O is
715. At 12 PPM (1000 font units scaled to 12 pixels), the rounded height of the H will be 8 pixels. The
height of the O will be 9 pixels. One pixel difference at this height means 8%. Much more than the
original 2%!
To avoid such an excessive difference between the rasterized heights of the
two types of characters, overshoots are suppressed and the size of O is
forced equal to the height of H at small PPM.