User Guide

FontLab 4
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Metrics Files
Information about a glyph’s width is usually located in font files. Kerning
information may also be included in the file. In TrueType and FontLab font
formats both metrics and kerning data are located in a single font file. In
Type 1 (PostScript) fonts the metrics and kerning data are located in
separate files.
There are two possible formats for the metrics files that are used with Type
1 fonts: AFM and PFM. AFM files (Adobe Font Metrics) are text files
containing all the metrics and kerning information for a given font. These
files are legible as text and can be edited in any text editor. PFM files
(Printer Font Metrics) are metrics and kerning files used by the Windows
operating system. They are binary files and cannot be read without special
utilities. AFM files are a standard format for the exchange of metrics
information for PostScript fonts. This information can be read directly by
several operating systems and programs.
In the Windows OS Multiple Master Type 1 fonts store metrics information
in another format. There is a binary Multiple Master Metrics file, which
usually has the file extension MMM and a text Multiple Master metrics file.
MMM files include information about the font’s axes and masters,
multiple-master data for glyphs’ metrics and kerning and other font header
data. The text metrics files have a composite structure: there is a linking
file that describes the font header, axes and masters information, and
separate AFM files (with metrics and kerning data) for each master font.
FontLab can import and export metrics and kerning information in any of
these formats.