N.B. An asterisk before a word means it has its own entry in the glossary.
A font rasterizer available as source code from Agfa (= Universal Font Scaling Technology) incorporating TrueType, Type 1 and Intellifont rasterizers.
An international standard for character mappings, based on a 16-bit index. On the Windows platform, TrueType's *'cmap' table maps Unicode character indices to *glyph indices within the font. Read more on the Unicode page at this site.
- units per em (or upem)
The notional size of the square whose lower left corner is at the origin of the *glyph coordinates in a TrueType font. The value (stored in the *'head' table, and often 2048) has a key role in scaling the glyph to different devices. The vital scaling factor, that multiplies master outline coordinates to produce pixel distances on a device, is:
pointsize * dpi_resolution / (72 * upem)
Thus the upem field can be regarded as the font's component of the scaling factor: everything else is under the control of the OS, the output device and the application. Unfortunately a few applications do not respect this rule for pointsize, preferring to calculate their own based on ascender and descender fields.
When converting to TrueType from other formats, it's not necessary to change the upem value to 2048 (as many conversion programs do). For example, conversions from Type 1 are better left at 1000.
TrueType Typography |