OpenType is a new font format codeveloped by Adobe and Microsoft.
OpenType format is an extension of TrueType format that can support either TrueType or PostScript font data and new typographic features. OpenType fonts containing PostScript data have an .OTF extension in the font file name, while TrueType-based OpenType fonts have a .TTF file name suffix.
OpenType fonts can be installed and used alongside PostScript Type 1 and TrueType fonts.
Similar to TrueType any OpenType font uses a single font file for all of its outline, metric, and bitmap data. The same font file works on Macintosh and Windows computers.
OpenType fonts are based on Unicode multi-byte character encoding that covers virtually all of the world's languages. That important TrueType advantage is now applicable to PostScript data as well.
OpenType can be digitally signed by manufacturer. Digital signature allows operating systems to identify the source and integrity of fonts.
Similar to TrueType, OpenType has an "embedding flag". This flag controls the level of permitted embedding of a font into a document.
OpenType fonts use efficient data compression technology: Adobe's Compact Font Format ('FF) for PostScript outline data and Agfa's MicroType Express for TrueType outline data. OpenType font files take less space on disks and less time when sending via Internet.
OpenType Advanced Typography
Because of the limitations of previous font technologies, support for expert character sets and multiple languages required separate font files. OpenType fonts provide far more typographic capabilities by combining base character sets, expert sets and extensive additional glyphs into one file.
The most significant advantage of the new technology is support of so-called OpenType features.
Central to a discussion of OpenType feature support lies the distinction between characters and glyphs. Characters are code points assigned by the Unicode standard, which represent the smallest semantic units of language, such as letters. Glyphs are specific forms that those characters can take. One character may correspond to several glyphs; the lowercase "a," the small cap "a" and the alternate swash lowercase "a" are all the same character, but they are three separate glyphs. One glyph can also represent multiple characters, as in case of the "ffi" ligature, which corresponds to a sequence of three characters: f, f and i.
OpenType layout features can be used to position or substitute glyphs. For any character, there is a default glyph and positioning behavior. Application of layout features to one or more characters may change positioning, or substitute a different glyph. For example, application of small capitals feature to the "a" would substitute the small cap "a" glyph for the usual lowercase "a" glyph. To access alternate glyphs in an OpenType font, an application provides a user interface that allows end-users to apply OpenType layout features to text. Applications that don't support Unicode or advanced Open-Type layout features can still access the basic glyph sets of OpenType fonts, which are analogous to the glyph sets in today's PostScript Type 1 fonts. The lowercase "a" character can be represented by multiple glyphs in an OpenType font.
OpenType support in Operating Systems and Applications
While most Macintosh and Windows applications are compatible with OpenType via ATM Light or native operating system support, Adobe InDesign and Adobe Photoshop were the first applications to provide advanced OpenType feature support. Other Adobe applications are expected to follow suit in the future. With InDesign and other OpenType-savvy applications you can turn on OpenType layout features that automatically substitute alternate glyphs in an OpenType font. Many of these OpenType layout features, such as automatic ligatures, small capitals, swashes and old-style figures, are accessed through the OpenType pop-up menu on the Character palette in InDesign. In addition, any alternate glyphs in OpenType fonts may be selected manually via the Insert Glyph palette.
Read more about OpenType support in special section.
OpenType in Win and Mac
OpenType support in Operating Systems and Applications
At first we must distinguish OpenType with PostSript data (OT/PS) and OpenType with TrueType data (OT/TT) because they work differently.
At second let's distinguish the levels of support:
- basic support - fonts can work just as standard Western fonts;
- multilingual support - fonts can be used in accordance with the Unicode encoding standard;
N.B. Be aware, even if an operating system has multilingual support, it does not mean that all applications automatically use advantages of that support and vise versa -- in a system with restricted multilingual support some applications work with fonts directly and get more then system offers.
- support of OT features - fonts can be used with respect to their abilities to substitute and position glyphs.
Windows 95, 98, ME work with OT/TT exactly as with standard TrueType fonts and provide restricted support of Unicode. Do not work with OT/PS as a native format, ATM 4.1.2 or later is required.
Windows 2000, XP give full multilingual support for OT/TT and for OT/PS (no ATM required) and restricted support of some OT features - substitutions and positioning glyphs for some complex scripts like Arabic, Devanagari,...
Mac OS Classic (7.x - 9.x) does not support OT/TT and has basic support for OT/PS with ATM 4.6.2 or later.
Mac OS X has multilingual support for both OT/TT and OT/PS. No ATM required.
OpenType Support In Applications
Full support of OpenType components for both OT/PS and OT/TT versions can be found just in Adobe InDesign and Adobe Photoshop 7.0.
- for OT/PS and OT/TT is realized in CorelDRAW 10 and 11; in MS Word for Windows 2003
- for OT/TT in MS Word for Windows 2000, XP; Adobe Illustrator 10 for Mac and PC
All other popular applications like Freehand, QuarkXPress still work with OpenType fonts like with standard Western fonts.