User Guide

FontLab 4
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O u t l i n e La ye r
The Outline layer is the most important of all the layers. It stores
information about the glyph shape while all the other FontLab editing
layers and most of the tools are designed to help you create good outlines.
Before we turn to the outline editing tools let’s talk about outline structure.
Units of Measurement
The coordinates of any object in the font are presented in a standard
measurement system. One unit of this system is called a font unit. The
scale of font units used in a particular font is the Units Per eM (UPM) font
parameter. The program that scales the font knows the UPM value of the
font and can use it to properly scale it. To get a text string of the same
visible size a font that has a larger UPM value must be scaled with a
smaller scale factor.
Usually Type 1 fonts have a UPM value of 1000 font units. Therefore, to get
a text string with a height of 100 pixels (assuming that we use a raster
output device) we would scale this font with a scale factor of 10%.
TrueType fonts usually have a UPM of 2048 units. So to get a text string of
100 pixels we would scale this font with a scale factor of 4.9%. Essentially
the UPM is nothing more than a base value used for proper font scaling
and as a base value for the font unit.