OpenType

Adobe and Microsoft continued to develop and refine OpenType over the next decade. Then, in late 2005, OpenType began migrating to an open standard under the International Organization for Standardization (ISO) within the MPEG group, which had previously (in 2003) adopted OpenType 1.4 by reference for MPEG-4.[5][7][8][9] Adoption of the new standard reached formal approval in March 2007 as ISO Standard ISO/IEC 14496-22 (MPEG-4 Part 22) called Open Font Format (OFF, not to be confused with Web Open Font Format).[10] It is also sometimes referred to as "Open Font Format Specification" (OFFS).[5] The initial standard was technically equivalent to OpenType 1.4 specification, with appropriate language changes for ISO.[11] The second edition of the Open Font Format was published in 2009 (ISO/IEC 14496-22:2009) and was declared "technically equivalent" to the "OpenType font format specification".[12][13] Since then, the Open Font Format and the OpenType specification have continued to be maintained in sync. OFF is a free, publicly available standard.[14]

By 2001 hundreds of OpenType fonts were on the market. Adobe finished converting their entire font library to OpenType toward the end of 2002. As of early 2005, around 10,000 OpenType fonts had become available, with the Adobe library comprising about a third of the total. By 2006, every major font foundry and many minor ones were developing fonts in OpenType format.

Unicode version 3.2 (published in 2002) introduced variation selectors as an encoding mechanism to represent particular glyph forms for characters.[15] Unicode did not, however, specify how text-display implementations should support these sequences. In late 2007, variation sequences for the Adobe-Japan1 collection were registered in the Unicode Ideographic Database,[16] leading to a real need for an OpenType solution. This resulted in development of cmap subtable Format 14, which was introduced in OpenType version 1.5.[17]

Unicode version 6.0 introduced emoji encoded as characters into Unicode in October 2010.[18] Several companies quickly acted to add support for Unicode emoji in their products. Since Unicode emoji are handled as text, and since color is an essential aspect of the emoji experience, this led to a need to create mechanisms for displaying multicolor glyphs.

Apple, Google and Microsoft independently developed different color-font solutions for use in OS X/iOS, Android and Windows. OpenType / OFF already had support for monochrome bitmap glyph, and so Google proposed that OFF be extended to allow for color bitmaps. This was the approach being taken by Apple, though Apple declined to participate in extending the ISO standard. As a result, Apple added the 'sbix' table to their TrueType format in OS X 10.7,[19] while Google proposed addition of the CBDT and CBLC tables to OFF.

Microsoft adopted a different approach than color bitmaps. Noting existing practice on the Web of layering glyphs of different color on top of one another to create multi-colored elements such as icons, Microsoft proposed a new COLR table to map a glyph into a set of glyphs that are layered, and a CPAL table to define the colors.

Adobe proposed yet another approach: add a new 'SVG ' table that can contain multi-color glyphs represented using Scalable Vector Graphics.

The Adobe, Microsoft and Google proposals were all incorporated into the third edition of OFF (ISO/IEC 14496-22:2015).[20] The new tables—CBDT, CBLC, COLR, CPAL, SVG—were added to OpenType version 1.7.[17]

While Microsoft originally supported only the COLR/CPAL color format, support for all of the different color formats, including Apple's 'sbix' format, was added to Microsoft Windows in the Windows 10 Anniversary Update.[21] The 'sbix' table was subsequently added to OpenType in version 1.8.[17]

Since at least version 1.4, the OpenType specification had supported “TrueType Collections”, a feature of the format that allows multiple fonts to be stored in a single file. Such a format is useful for distributing an entire typeface (font family) in just one file.

By combining related fonts into a single file, font tables that are identical can be shared, thereby allowing for more efficient storage. Also, individual fonts have a glyph-count limit of 65,535 glyphs, and a Collection file provides a "gap mode" mechanism for overcoming this limit in a single font file. (Each font within the collection still has the 65,535 limit, however.) A TrueType Collection file would typically have a file extension of “.ttc”.

However, the specification only described collection files being used in conjunction with glyphs that are represented as TrueType outlines or as bitmaps. The potential existed to provide the same storage and glyph-count benefits to fonts that use CFF-format glyphs (.otf extension). But the specification did not explicitly allow for that.

In 2014, Adobe announced the creation of OpenType Collections (OTCs), a Collection font file that combines fonts that use CFF-format glyphs.[22] This provided significant storage benefits for CJK fonts that Adobe and Google were jointly developing. For example, the Noto fonts CJK OTC is ~10 MB smaller than the sum of the four separate OTFs of which it is composed.[23] The use of a Collection also allowed for combining a very large number of glyphs into a single file, as would be needed for a pan-CJK font.[24]

Explicit support for Collections with CFF-format glyphs was incorporated into the OpenType specification in version 1.8.[17] To reflect this more-inclusive applicability, the term “OpenType Collection” was adopted, superseding “TrueType Collection”.

On September 14, 2016, Microsoft announced the release of OpenType version 1.8. This announcement was made together with Adobe, Apple, and Google at the ATypI conference in Warsaw.[25] OpenType version 1.8 introduced “OpenType Font Variations”, which adds mechanisms that allow a single font to support many design variations.[26] Fonts that use these mechanisms are commonly referred to as “OpenType variable fonts”.

OpenType Font Variations re-introduces techniques that were previously developed by Apple in TrueType GX, and by Adobe in Multiple Master fonts. The common idea of these formats is that a single font includes data to describe multiple variations of a glyph outline (sometimes referred to as “masters”), and that at text-display time, the font rasterizer is able to interpolate or “blend” these variations to derive a continuous range of additional outline variations.[27]

The concept of fully parametric fonts had been explored in a more general way by Donald E. Knuth in the METAFONT system, introduced in 1978.[28] That system and its successors were never widely adopted by professional type designers or commercial software systems.[29] TrueType GX and Multiple Master formats, OpenType Font Variations’ direct predecessors, were introduced in the 1990s, but were not widely adopted, either. Adobe later abandoned support for the Multiple Master format.[30] This has led to questions as to whether a re-introduction of similar technology could succeed. By 2016, however, the industry landscape had changed in several respects. In particular, emergence of Web fonts and of mobile devices had created interest in responsive design and in seeking ways to deliver more type variants in a size-efficient format. Also, whereas the 1990s was an era of aggressive competition in font technology, often referred to as “the font wars”, OpenType Font Variations was developed in a collaborative manner involving several major vendors.[31]

Font Variations is integrated into OpenType 1.8 in a comprehensive manner, allowing most previously-existing capabilities to be used in combination with variations. In particular, variations are supported for both TrueType or CFF glyph outlines, for TrueType hinting, and also for the OpenType Layout mechanisms. The only parts of OpenType for which variations are not supported but might potentially be useful are the SVG table for color glyphs, and the MATH table for layout of mathematical formulas. OpenType 1.8 made use of tables originally defined by Apple for TrueType GX (the avar, cvar, fvar and gvar tables). It also introduced several new tables, including a new table for version 2 of the CFF format (CFF2), and other new tables or additions to existing tables to integrate variations into other parts of the font format (the HVAR, MVAR, STAT and VVAR tables; additions to the BASE, GDEF and name tables).[17]

OpenType support may be divided into several categories. Virtually all applications and most modern operating systems have basic Roman support and work with OpenType fonts just as well as other, older formats. Benefits beyond basic Roman support include extended language support through Unicode, support for complex writing scripts such as Arabic and the Indic languages, and advanced typographic support for Latin script languages such as English.

Amongst Microsoft's operating systems, OpenType TT fonts (.TTF) are backward compatible and therefore supported by all Microsoft Windows versions starting with Microsoft Windows 3.1. OpenType PS fonts (.OTF) are supported in all Windows versions starting with Microsoft Windows 2000; Adobe Type Manager is required to be installed on Microsoft Windows 95/98/NT/Me for basic Roman support (only) of OpenType PS fonts.

Extended language support via Unicode for both OpenType and TrueType is present in most applications for Microsoft Windows (including Microsoft Office Publisher, most Adobe applications, and Microsoft Office 2003, though not Word 2002), CorelDRAW X3 and newer, and many Mac OS X applications, including Apple's own such as TextEdit, Pages and Keynote. It is also widely supported in free operating systems, such as Linux (e.g. in multiplatform applications like AbiWord, Gnumeric, Calligra Suite, Scribus, OpenOffice.org 3.2 and later versions,[32] etc.).

OpenType support for complex written scripts has so far mainly appeared in Microsoft applications in Microsoft Office, such as Microsoft Word and Microsoft Publisher. Adobe InDesign provides extensive OpenType capability in Japanese but does not directly support Middle Eastern or Indic scripts—though a separate version of InDesign is available that supports Middle Eastern scripts such as Arabic and Hebrew. Undocumented functionality in many Adobe Creative Suite 4 applications, including InDesign, Photoshop and Illustrator, enables Middle Eastern, Indic and other languages, but is not officially supported by Adobe, and requires third-party plug-ins to provide a user interface for the features.

Advanced typographic support for Latin script languages first appeared in Adobe applications such as Adobe InDesign, Adobe Photoshop and Adobe Illustrator. QuarkXPress 6.5 and below were not Unicode compliant. Hence text in these versions of QuarkXPress that contains anything other than WinANSI/MacRoman characters will not display correctly in an OpenType font (nor in other Unicode font formats, for that matter). However, in QuarkXPress 7, Quark offered support similar to Adobe's. Corel's CorelDRAW introduced support for OpenType typographic features in version X6. Mellel, a Mac OS X-only word processor from Redlers, claims parity in typographic features with InDesign, but also extends the support to right-to-left scripts; so does the Classical Text Editor, a specialized word processor developed at the Austrian Academy of Sciences.

As of 2009, popular word processors for Microsoft Windows did not support advanced OpenType typography features. Advanced typography features are implemented only in high-end desktop publishing software. The text engine from Windows Presentation Foundation, which is a managed code implementation of OpenType, is the first Microsoft Windows API to expose OpenType features to software developers, supporting both OpenType TrueType, and OpenType CFF (Compact Font Format) fonts. It supports advanced typographic features such as ligatures, old-style numerals, swash variants, fractions, superscript and subscript, small capitalization, glyph substitution, multiple baselines, contextual and stylistic alternate character forms, kerning, line-level justification, ruby characters etc.[33] WPF applications automatically gain support for advanced typography features. OpenType ligatures are accessible in Microsoft Office Word 2010.[34]

Windows 7 introduced DirectWrite, a hardware accelerated native DirectX API for text rendering with support for multi-format text, resolution-independent outline fonts, ClearType, advanced OpenType typography features, full Unicode text, layout and language support and low-level glyph rendering APIs.[35]

On Mac OS X, AAT-supporting applications running on Mac OS X 10.4 and later, including TextEdit and Keynote, get considerable OpenType support. Apple's support for OpenType in Mac OS X 10.4 included most advanced typographic features necessary for Latin script languages, such as small caps, oldstyle figures, and various sorts of ligatures, but it did not yet support contextual alternates, positional forms, nor glyph reordering as handled by Microsoft's Uniscribe library on Windows. Thus, Mac OS X 10.4 did not offer support for Arabic or Indic scripts via OpenType (though such scripts are fully supported by existing AAT fonts). Mac OS X 10.5 has improved support for OpenType and supports Arabic OpenType fonts. Gradually, the OpenType typography support has improved on newer Mac OS X versions (e.g. Mac OS X 10.10 can handle much better long contextual glyph substitutions).

Bitstream Panorama, a line layout and text composition engine from Bitstream Inc., provides complete OpenType support for compact and standard Asian fonts, Arabic, Hebrew, Indic, Thai and over 50 other worldwide languages. The application supports key OpenType tables required for line layout, such as BASE, glyph definition (GDEF), glyph positioning (GPOS), and glyph substitution (GSUB). Panorama also offers complete support for advanced typography features, such as ligatures, swashes, small caps, ornaments, ordinals, superiors, old style, kerning, fractions, etc.

In free software environments such as Linux, OpenType rendering is provided by the FreeType project, included in free implementations of the X Window System such as X.org. Complex text handling is provided either by pango (calling HarfBuzz) or Qt. The XeTeX and LuaTeX systems allow TeX documents to use OpenType fonts, along with most of their typographic features. Linux version of LibreOffice 4.1 and newer supports many OpenType typography features, because it began to use more sophisticated HarfBuzz text shaping library.[36]

Script tags identify the scripts (writing systems) represented in an OpenType font. Each tag corresponds to contiguous character code ranges in Unicode. A script tag can consist of 4 or fewer lowercase letters, such as arab for the Arabic alphabet, cyrl for the Cyrillic script and latn for the Latin alphabet. The math script tag, added by Microsoft for Cambria Math, has been added to the specification.[39][40]

Language system tags identify the language systems supported in an OpenType font. Examples include ARA for Arabic, ESP for Spanish, HYE for Armenian, etc. In general, the codes are not the same as ISO 639-2 codes.[41]

A list of OpenType features with expanded descriptions is given list of typographic features.

Baseline tags have a specific meaning when used in the horizontal writing direction (used in the 'BASE' table's HorizAxis table), vertical writing direction (used in the 'BASE' table's VertAxis table), or both.

A set of tables that mirrors TeX math font metrics relatively closely was added by Microsoft initially to Cambria Math for supporting their new math editing and rendering engine in Office 2007 and later.[42][43] This extension was added to the ISO standard (ISO/IEC CD 14496-22 3rd edition) in April 2014.[44] Additional (usage) details are available in the Unicode technical report 25[45] and technical note 28.[46] Some of the new technical features (not present in TeX), such as "cut-ins" (which allows kerning of subscripts and superscripts relative to their bases[47]) and stretch stacks[48] have been patented by Microsoft.[49][50][51] Windows 8 supports OpenType math outside MS Office applications via the RichEdit 8.0 component.[52]

Besides Microsoft products, XeTeX and LuaTeX also have some level of support for these tables; support is more limited in XeTeX because it uses the traditional TeX math rendering engine (thus it cannot fully use some of the new features in OpenType math that extend TeX), while LuaTeX takes a more flexible approach by changing some of the internals of TeX's math rendering; in the words of Ulrik Vieth (2009): "More precisely, while XeTeX only provides access to the OpenType parameters as additional \fontdimens, LuaTeX uses an internal data structure based on the combined set of OpenType and TeX parameters, making it possible to supply missing values which are not supported in either OpenType math fonts or traditional TeX math fonts."[48] In 2013, XeTeX also gained support for cut-ins.[53]

The Gecko rendering engine used by the Firefox web browser also supports some OpenType math features in its MathML implementation.[54][55]

As of 2010, the set of fonts that supported OpenType math was fairly limited. Besides Cambria Math, three free fonts were available: Asana-Math, Neo Euler, and XITS.[56] More recently the Latin Modern and TeX Gyre fonts (an "LM-ization" of the standard PostScript fonts[57]) have also gained support for OpenType math.[58][59][60][61] As of 2014 the number of OpenType math fonts is still fairly limited.[62] A more up-to-date list is maintained on Mozilla's web site.[63]

Emergence of Unicode emoji created a need for TrueType and OpenType formats to support color glyphs. Apple added a color extension in Mac OS X Lion (and also to iOS 4+). Fonts were extended with colored PNG images within the sbix table.[64][65][66] Google used a similar extension with embedded color bitmap images contained within a pair of tables, the CBDT and CBLC tables.[67] The Google version is implemented in FreeType 2.5.[68]

In Windows 8.1 Microsoft also added color support to fonts, first implemented in the Segoe UI Emoji font.[65][69][70][71] Microsoft's implementation, however, relies entirely on vector graphics:[65][72] two new OpenType tables were added in Microsoft's implementation: the COLR table allows layered glyphs and the CPAL (“Color Palette”) actually defines the colors for the layers. The multi-layer approach allows a backwards compatible implementation as well as varying the rendering depending on the color context surrounding the glyphs.[65] According to Adam Twardoch: "At TypeCon [2013], Greg Hitchcock clarified the envisioned roles of the palettes: first palette is used by default for “dark on light” color situations while second palette is intended for use in “light on dark” situations. Additional palettes should be selectable by the user."[68]

Mozilla and Adobe developed a different vector-based extension by adding embedded SVG documents (supporting color but also animations) into the SVG table. The SVG table also allowed for using color palettes defined in the CPAL table.[73] Support was first implemented in Firefox 26.[67]

Adobe, Mozilla, Google and Microsoft each submitted their color extensions for standardization thorough ISO/IEC 14496-22.[74] The new tables for each of these were then added into OpenType version 1.7.[75] Apple's sbix table was originally supported only in AAT fonts, but it was later added into OpenType version 1.8.[76] Microsoft Windows 10 Anniversary Update was the first OS to support all four color font extensions, and Microsoft Edge was the first browser to do so.[77][78]

In OpenType Version 1.8.3, the specification for the SVG table was revised to be more constrained, providing more clarity for implementations and better interoperability. Apple is supporting the revised specification in Safari 12, iOS12 and macOS 10.14.[79] The implementation in Microsoft Windows also conforms to this revision.