OpenType
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OpenType is a scalable computer font format initially developed by Microsoft, later joined by Adobe Systems. OpenType was first announced in 1996, with significant number of OpenType fonts starting to ship in 2000-2001. Adobe completed conversion of their entire font library to OpenType around the end of 2002. As of early 2005, there are over 7,000 fonts available in OpenType format, with Adobe's library making up for about 1/3 of the total.
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History
OpenType was intended by Microsoft to be the successor to the TrueType font format developed by Apple Computer and licensed by Microsoft. Microsoft tried to license Apple's advanced typography technology, "GX Typography," and upon being refused turned to develop its own technology dubbed "TrueType Open" and later on "OpenType". Adobe Systems joined the OpenType camp later, adding support for its PostScript Type 1 fonts.
Description
OpenType uses the general structure of a TrueType font, but adds several unique options which enhance the font's typographical abilities. An OpenType font can include either TrueType outlines or PostScript-style outlines (though stored in the CFF/Type 2 format).
OpenType has several distinctive features:
- the font encoding is based on Unicode and can support any language (or multiple languages at once)
- OpenType fonts can have up to 65,536 glyphs
- fonts can have advanced typographic features, which allow proper typographic treatment of complex languages, and advanced typographic effects for simpler languages, such as English.
Comparison to other formats
Compared with Apple Computer's "GX Typography" now called Apple Advanced Typography, or AAT, OpenType is slightly inferior with most typographical options, but offers superior language-related options and support.
From a font developer's perspective, OpenType is much easier to develop for than GX was. First, the simple declarative substitutions and positioning of OpenType are much simpler to understand and code for than GX's state tables. Second, Adobe's strategy of licensing at no charge the source code developed for its own font development allowed third-party font editing applications such as FontLab and FontMaster to relatively easily add support. Although Adobe's text-driven coding support is not as visual as Microsoft's separate tool, VOLT (Visual OpenType Layout Tool), the integration with the tools being used to make the fonts has been well received.
OpenType support
OpenType support may be divided into several categories: virtually all applications and most operating systems work with OpenType fonts just as well as other, older formats. What is of particular interest is: extended language support through Unicode, support for "complex" languages such as Arabic and the Indic languages, and advanced typographic support for western languages such as English.
As of early 2005, extended language support via Unicode for both OpenType and TrueType is present in most Windows applications (including Microsoft Office, Publisher and most Adobe applications), and many Mac OS applications, especially Apple's own such as TextEdit and Keynote.
OpenType support for complex languages has so far mainly appeared in Microsoft applications such as Office and Publisher. Adobe InDesign provides extensive OpenType capability in Japanese but does not directly support Middle Eastern or Indic scripts.
Advanced typographic support for western languages has so far mainly appeared in Adobe applications such as Adobe InDesign, Adobe Photoshop and Adobe Illustrator. However, competitor Quark has announced that they will offer similar support in QuarkXPress 7 (release date not yet known).
SING gaiji solution
In 2005, Adobe shipped a new technology in their Creative Suite applications bundle that puports to solve the so-called gaiji problem. Ideographic writing scripts such as Chinese and Japanese do not have fixed collections of characters. They use thousands of glyphs commonly and tens of thousands less commonly. Not all glyphs ever invented and used in far eastern literature have even been catalogued. A typical font might contain 8,000 to 15,000 of the most commonly used glyphs. From time to time, though, an author needs a glyph not present in the font of choice. Such missing characters are known in Japan as gaiji, and they often disrupt work.
Several ways to deal with gaiji have been devised. Solutions that treat them as characters usually assign arbitrary Unicode values to them in the PUA (private use area). Such characters cannot be used outside the environment in which the association of the private Unicode to the glyph shape is known. Documents based on them are not portable. Other installations treat gaiji as graphics. This can be cumbersome because text layout and composition cannot apply to graphics. They cannot be searched for. Often their rendering looks different than surrounding characters because the machinery for rendering graphics usually is different than the machinery for rendering glyphs from fonts.
The SING technology that made its debut with Adobe's Creative Suite II allows for the creation of glyphs, each packaged as a stand-alone font, after a fashion. Such a packaged glyph is called a glyphlet. The format, which Adobe has made public, is based on OpenType. The package consists of the glyph outline in TrueType or CFF form; standard OpenType tables declaring the glyph's metrics and behavior in composition; and metadata, extra information included for identifying the glyphlet, its ownership, and perhaps pronunciation or linguistic categorization.
The SING (smart, independent glyphlets) specification states that glyphlets are to travel with the document they are used in. That way documents are portable, leaving no danger of characters in the document that cannot be displayed. Because glyphlets are essentially OpenType fonts, standard font machinery can render them. The SING specification also describes an XML format that includes all the data necessary for reconstituting the glyphlet in binary form. A typical glyphlet might require 1 to 2 kilobytes to represent.
OpenType is a registered trademark of Microsoft Corporation.
See also
- Uniscribe (Windows multilingual text rendering engine)
- Apple Type Services for Unicode Imaging (New Macintosh multilingual text rendering engine)
- WorldScript (Old Macintosh multilingual text rendering engine)
- Pango (Open source multilingual text rendering engine)
External links
- Adobe main OpenType page: http://www.adobe.com/type/opentype
- The OpenType Specification (Adobe): http://partners.adobe.com/asn/developer/opentype/main.html
- The OpenType Specification (Microsoft): http://www.microsoft.com/typography/otspec/default.htm
- Main Microsoft Typography site: http://www.microsoft.com/typography
- Microsoft information about font development: http://www.microsoft.com/typography/creators.htm
- Typo.cz Information on Central European typography and fonts: http://euro.typo.cz
- Diacritics Project — All you need to design a font with correct accents: http://diacritics.typo.czde:OpenType