OpenType - Description

Description

  • TrueType outlines use quadratic Bézier splines.

  • CFF outlines use cubic Bézier splines.

OpenType uses the general sfnt structure of a TrueType font, but it adds several smartfont options that enhance the font's typographic and language support capabilities.

The glyph outline data in an OpenType font may be in one of two formats: either TrueType format outlines in a 'glyf' table, or Compact Font Format (CFF) outlines in a 'CFF ' table. (The table name 'CFF ' is four characters long, ending in a space character.) CFF outline data is based on the PostScript language Type 2 font format. However, the OpenType specification does not support the use of PostScript outlines in a TrueType Collection font file.

For many purposes, such as layout, it doesn't matter what the outline data format is, but for some purposes, such as rasterisation, it is significant. The OpenType standard does not specify the outline data format: rather, it accommodates any of several existing standards. Sometimes terms like "OpenType (PostScript flavor)", "Type 1 OpenType", "OpenType CFF", or "OpenType (TrueType flavor)" are used to indicate which outline format a particular OpenType font file contains.

OpenType has several distinctive characteristics:

  • Accommodates the Unicode character encoding (as well as others), so that it can support any writing script (or multiple scripts at once).
  • Accommodates up to 65,536 glyphs.
  • Advanced typographic "layout" features which prescribe positioning and replacement of rendered glyphs. Replacement features include ligatures; positioning features include kerning, mark placement, and baseline specification.
  • Cross-platform font files, which can be used without modification on Mac OS, Windows and Unix systems.
  • If no additional glyphs or extensive typographic features are added, OpenType CFF fonts can be considerably smaller than their Type 1 counterparts.

Read more about this topic:  OpenType

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