Fonts, Open Type Fonts, True Type Fonts, Free Type Fonts
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 its entire font library to OpenType around the end of 2002. As of early 2005, there are around 10,000 fonts available in OpenType format, with Adobe's library making up under a third of the total.
OpenType uses the general "sfnt" structure of a TrueType font, but it adds several smartfont options which enhance the font's typographical abilities. An OpenType font can include either TrueType outlines or PostScript-style outlines (the latter stored in the compact CFF/Type 2 font format).
OpenType has several distinctive features:
OpenType Layout tags are 4-byte character strings that identify the scripts, language systems, features and baselines in a OpenType Layout font. Microsoft's Layout tag registry establishes conventions for naming and using these tags.
Comparison to other formats
Compared with Apple Computer's "GX Typography" - now called Apple Advanced Typography (AAT) - OpenType offers less flexibility in typographic options, but superior language-related options and support.
OpenType has been much more successful than AAT. There are many more fonts and supporting applications, despite AAT being an older technology. The single-platform nature of AAT and the lack of support from any major software vendor other than Apple itself are both likely factors in this.
From a font developer's perspective, OpenType is, for many common situations, easier to develop for than AAT. First, the simple declarative substitutions and positioning of OpenType are more readily understood than AAT's more complex (but powerful) 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 add support with relative ease. 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.
Another difference is that an OpenType support framework (such as Microsoft's Uniscribe) needs to provide a fair bit of knowledge about special language processing issues to handle (for example) Arabic. With AAT, the font developer of an AAT font has to encapsulate all that expertise in the font. This means that AAT can handle any arbitrary language, but that it requires more work and expertise from the font developers. On the other hand, OpenType fonts are easier to make, but can only support certain complicated languages if the application or operating system knows how to handle them.
Previous to supporting OpenType, Adobe promoted multiple master fonts for high-end typography. Multiple master fonts lacked the controls for alternate glyphs and languages provided by OpenType, but provided more control over glyph shape.
TrueType is an outline font standard originally developed by Apple Computer in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript. The primary strength of TrueType was originally that it offered font developers a high degree of control over precisely how their fonts are displayed, right down to particular pixels, at various font heights. (With widely varying rendering technologies in use today, pixel-level control is no longer certain.)
TrueType systems include a virtual machine that executes programs inside the font, processing the "hints" of the glyphs. These distort the control points which define the outline, with the intention that the rasterizer produces fewer undesirable features on the glyph. Each glyph's hinting program takes account of the size (in pixels) at which the glyph is to be displayed, as well as other less important factors of the display environment.
Although incapable of receiving input and producing output as normally understood in programming, the TrueType hinting language does offer the other prerequisites of programming languages: conditional branching (IF statements), looping an arbitrary number of times (FOR- and WHILE-type statements), variables (although these are simply numbered slots in an area of memory reserved by the font), and encapsulation of code into functions. Special instructions called delta hints are the lowest level control, moving a control point at just one pixel size.
Good TrueType glyph programming techniques are meant to do as much as possible using variables defined just once in the whole font (e.g., stem widths, cap height, x-height). This means avoiding delta instructions as much as possible. This helps the font developer to make major changes (e.g., the point at which the entire font's main stems jump from 1 to 2 pixels wide) most of the way through development.
Making a very well-hinted TrueType font remains a significant amount of work, despite the increased user-friendliness of programs for adding hints to fonts compared with the early 1990s. Many TrueType fonts therefore have only rudimentary hints, or have hinting automatically applied by the font editor, with variable end results.
FreeType is a software library that implements a font engine. It is used to rasterize characters into bitmaps and provides support for other font-related operations.
As of May 2006, the latest version of FreeType is FreeType 2.2.1, which supports an assortment of font formats, including TrueType, Type 1, and OpenType. FreeType is open source, available for use under the GNU General Public License or a license similar to the original BSD license (with the advertising clause).
PostScript (PS) is a page description language and programming language used primarily in the electronic and desktop publishing areas.
PostScript broke with tradition by combining the best features of both printers and plotters. Like plotters, PostScript offered high quality line art and a single control language that could be used on any brand of printer. Like dot-matrix printers, PostScript offered simple ways to generate pages of text and raster graphics. Unlike either, PostScript could place all of these types of media on a single page, which offered far more flexibility than any printer or plotter previously had.
PostScript went beyond the typical printer control language and was a complete programming language of its own. Many applications can transform a document into a PostScript program whose execution will result in the original document. This program can be sent to an interpreter in a printer, which results in a printed document, or to one inside another application, which will display the document on-screen. Since the document-program is the same regardless of its destination, it is called device-independent.
PostScript is also noteworthy for implementing on-the fly rasterization; everything, even text, is specified in terms of straight lines and cubic Bézier curves (previously found only in CAD applications), which allows arbitrary scaling, rotating and other transformations. When the PostScript program is interpreted, the interpreter converts these instructions into the dots needed to form the output. For this reason PostScript interpreters are also sometimes called PostScript Raster Image Processors, or RIPs.
A design for a set of characters. Popular typefaces include Times Roman, Helvetica, and Courier. The typeface represents one aspect of a font. The font also includes such characteristics as size, weight, italics, and so on.
There are two general categories of typefaces: serif and sans serif. Sans serif typefaces are composed of simple lines, whereas serif typefaces use small decorative marks to embellish characters and make them easier to read. Helvetica is a sans serif type and Times Roman is a serif type.
A small decorative line added as embellishment to the basic form of a character. Typefaces are often described as being serif or sans serif (without serifs). The most common serif typeface is Times Roman. A common sans serif typeface is Helvetica.
Pronounced SAN-SERR-if. A category of typefaces that do not use serifs, small lines at the ends of characters. Popular sans serif fonts include Helvetica, Avant Garde, Arial, and Geneva. Serif fonts include Times Roman, Courier, New Century Schoolbook, and Palatino.
According to most studies, sans serif fonts are more difficult to read. For this reason, they are used most often for short text components such as headlines or captions.
Some fonts contain the abbreviations such as LT, MT, FF or EF in the name. These abbreviations represent the name of the foundry and should not be confused with the font weight. For example LT stands for Linotype, MT stands for Monotype, FF stands for FontFont and EF stands for Elsner + Flake.Read more