Open Type Versus True Type Fonts Computer Science Essay

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TrueType (TT), PostScript® Type 1 (Type 1) and Open Type® are all multi-platform outline font standards for which the technical specifications are openly available. "Multi-platform" means that both font types are usable on multiple sorts of computer systems. "Outline font" means that they describe letter shapes ("glyphs") by means of points, which in turn define lines and curves. This representation is resolution independent, meaning that outlines, by their very nature, can be scaled to pretty much any arbitrary size. Depending on the particular program being used and the operating system it's run under, there may be upper and lower limits to the size the font can be scaled to, but few users will ever encounter these limits.

An outline font must be represented by the dots of the output device, whether it's screen pixels or the dots of a laser, ink-jet or wire-pin printer. The process of converting the outline to a pattern of dots on the grid of the device is called "rasterization."

When there aren't enough dots making up the glyph (such as at small sizes or low resolutions),

there can be inconsistencies in the representation of certain letter features, at a single size, due to different rounding based on how the outline happens to sit on the grid. A common form of this is that the widths of the letter stems can vary when they shouldn't. Worse, key features of the glyphs can disappear at small sizes.

However, Type 1, TrueType and Open Type fonts all have a means of dealing with these inconsistencies, called "hinting." This consists of additional information encoded in the font to help prevent these problems.

Brief History

PostScript and the Type font format predate TrueType by about six years (with Open Type being

a much later amalgamation of the two formats). First, we had many different formats for digital fonts, none of which were standardized. Then Apple adopted the Adobe® PostScript page description language (PDL) for its Apple LaserWriter printer in 1985. It is, combined with the introduction of PageMaker®, the first desktop publishing software, sparked a revolution in

page layout technology.

Soon the PostScript language was adopted for use in higher-end image setting devices, and became the native operating mode and language of many graphics programs as well. The command structure of the PostScript language was publicly available, so it was possible for someone to build a PostScript interpreter to compete with Adobe's rasterizing software. But

it wouldn't be able to interpret the hints in Type 1 fonts. This was because the PostScript font specification for Type 1 fonts, which included hinting, was not publicly available. Adobe had only released the specifications for Type 1 fonts. Type 1 fonts were a more general format, but Type 3 was smaller, faster, and had a native hinting structure (of which see more below).

It rapidly became obvious to the major system software creators (Apple, Microsoft, and later IBM) that it was important to have scaleable font technology supported at the level of the operating system itself. This would allow much better screen display, compared to pre-made bitmaps which would only look good at a few sizes, and would be jagged at all others. So in the late 1980s, Apple developed its own scaleable font technology, First code-named Royal,

and later introduced as TrueType.

Apple traded the technology to Microsoft in exchange for the latter's TrueImage PostScript clone technology (which was buggy at the time, and never used by Apple, although it has surfaced in various later incarnations). The TrueType specifications were made public, and TrueType was built into the next versions of the Mac and Windows® operating systems, released in 1991.

Adobe's response started with the release of the long-protected specifications for the PostScript Type 1 font format in March 1990. This was followed by introduction of Adobe Type Manager® (ATM®) software in mid-1990. ATM scales PostScript Type 1 fonts for screen display, and for imaging on non- PostScript printers.

In early 1991, TrueType for the Mac became available, followed by the Windows 3.1 implementation (the Windows scaler was and remains slightly more Accurate / efficient than the Mac version, though it's nothing a normal user is likely to notice). Now, with either TrueType or ATM, Mac users (and later Windows and OS/2 users) could actually see on-screen at

any size what the font output would look like.

Technical Differences

The first difference between TrueType and PostScript fonts is their use of different sorts of mathematics to describe their curves. Open Type fonts can have either kind of outlines, with their respective advantages and disadvantages.

Some articles have said that TrueType fonts require more points than PostScript, or that they take longer to rasterize because the math is more complicated. In fact, the math is simpler (quadratics are simpler than cubics). Although a few shapes take fewer points in TrueType than in PostScript (a perfect circle takes twelve points in PostScript vs. eight in TrueType), in practice the shapes in real-world fonts all tend to take more points in TrueType, it's true that most fonts will end up using more points in TrueType, even if the kind of mathematics used to describe the curves is simpler.

The primary advantage of TrueType over Type 1 fonts is the fact that TrueType has the potential for better hinting. Mind you, PostScript Type 1 hints handle a lot: vertical and horizontal features, overshoots, stem snaps, equal counters, and shallow curves ("flex"). Several of these can have a threshold pixel size at which they activate.

However, TrueType hints can do all that PostScript can, and almost anything else, as defined by the very flexible instructions of the TrueType language. This includes controlling diagonals, and moving specified points on the glyph outlines at specific arbitrary sizes to improve legibility. This ability to move points at a specific point size allows font production staff to hand-tune the bitmap pattern produced by the out-line at any specified size. Or at least it used to; more recent divergences in TrueType rasterizing between different players (including Apple and Microsoft) make this a little more uncertain.

This difference in hinting philosophy is really symptomatic of a larger philosophical difference. PostScript uses "dumber" fonts and a "smarter" interpreter, while TrueType uses relatively smarter fonts and a dumber interpreter. This means that PostScript hints tell the rasterizer what features ought to be controlled, and the rasterizer interprets these using its own "intelligence" to decide how to do it. ere-fore, when someone upgrades their PostScript interpreter, the rasterization can be improved.

Contrariwise, TrueType puts all the hinting information into the font to control exactly how it will appear when rasterized. Some TT aficionados prefer to call TrueType hints "instructions," partly in reference to the full-featured nature of the TrueType programming language, but also to clarify the role of this information. As Jelle Bosma of Agfa Mono- type says, "I don't hint at what I want to happen-I tell the font what to do."

us the TrueType font producer has the potential for very ne control over what happens when the font is rasterized under different conditions. However, it requires serious effort, expertise, and high-end tools for a font developer to actually take advantage of this greater hinting potential. Also, making major changes to the TrueType rasterizer while displaying existing fonts at their best would seem to be difficult to manage.

Until recently, the other advantage of TrueType was that it was the font format supported directly by the Ma c and Windows operating systems, while Type 1 required an add-on. These operating systems will rasterize TrueType fonts for the screen, and send them to printers, whether as bitmaps or in some font format the printer understands.

Scaling either PostScript fonts, or Open Type fonts with PostScript outlines, on Mac OS 8/9 and Windows 95/98/ME, requires the Adobe Type Manager (ATM) software, which handles the rasterizing to the screen, and rasterizes or converts the fonts for non- PostScript printers. (Technically, Mac users don't require ATM to use PostScript fonts on PostScript printers, but ATM is required to display the font Accurately on screen at arbitrary sizes.) ATM is freely available : the "Light" version is a free download from Adobe's Web site, and also comes with many Adobe applications.

However, in Windows 2000 and XP, and Mac OSX, the PostScript Type1 and Open Type CFF support is built in, just like the TrueType support has long been. So this former advantage is rapidly vanishing.

A smaller, but consistent, advantage of Open Type and TrueType has to do with the physical storage of the fonts. Open Type and TrueType fonts have all the data in a single file. PostScript Type 1 fonts require two separate files : one contains the character out-lines, and the other contains metrics data (character widths and kern pairs). On the Macintosh, Mac OS 8.1 and earlier requires Type 1 fonts to have not only the outline font, but also a bit-mapped screen font in at least one size, which contains the metrics data. For Windows systems using PostScript, a "PFB" file contains the outlines, while a "PFM" file carries the metrics.

The system-independent "AFM" metrics file can be converted to a Windows PFM file upon installation by ATM, or can be used by a font editing program along with the outline to create a screen font for the Mac that includes any kerning pairs in the original. On the other hand, PostScript's pair of files are often smaller than TrueType's single file. The size difference ranges from only a 5% savings for an average font, to as much as a doubling of size for True Type fonts that actually have extensive "hinting" instructions.

Also, most high-end output devices use PostScript as their internal page description language. PostScript fonts can be sent directly to these devices. It used to be the case that TrueType fonts were either down-loaded as bitmaps or required that the TrueType rasterizer be downloaded as a PostScript program, which slowed printing a bit.

Further Practical Differences

Many of the theoretical advantages of TrueType are not actually realized in most commercially available TrueType fonts. PostScript backers point to a number of problems that still make PostScript fonts a better solution for many users. Besides the abovementioned issue of the language of the output device, there are four other practical issues that even the score for PostScript: First, at present many of the commercially avail-able TrueType fonts one sees at the software mega-mart are of poor quality, coming in "zillion-fonts-for-a-buck" collections. Many of these fonts were originally shareware or public domain PostScript fonts, and were converted to TrueType using some basic automatic utility. The outlines and hinting are no better than they were in the PostScript versions, and will super slightly in almost any automatic con-version. Usually in the case of extremely cheap collections, they weren't the best quality* PostScript fonts even before conversion to TrueType. Of course, TrueType backers point out that often these fonts were available before; it's simply the availability of a universal font scaling technology that makes discount fonts for the masses practical, and of course they are more likely to be released in the most widely available format.

Second is the issue of easy-to-use tools. On the plus side, there is finally a retail font editor with native TrueType support (Font Lab 3), as well as Microsoft's Visual TrueType (VTT) hinting tool.

However, regardless of the specific tools used, achieving first-class hinting in TrueType currently requires intensive manual coding on a glyph-by-glyph basis. This requires substantial time and expertise on the part of the person doing the hinting.

As a result, high-quality TrueType fonts are currently only available from a handful of vendors, and only a minority of even those fonts really exploit the potential of TrueType hinting. Third, TrueType's hinting advantage only matters when hinting matters: when outputting to low-resolution devices, or for screen display. The increasing, widespread use of 600 dpi and better laser printers makes this less critical for print work. On the other hand, the increasing importance of screen displays for so many purposes including multimedia, the Internet, and electronic books makes hinting more important.

Fourth, PostScript has some advantages simply from being the longer-established standard, especially for serious graphic arts work. Service bureaus are standardized on, and have large investments in, PostScript fonts. Most of the fonts which have "expert sets" of old style figures, extra ligatures, true small capitals and the like are in PostScript Type 1

format.

Although most major vendors have TrueType fonts, not all offer their entire libraries in both for-mats. Agfa Mono type and Bit stream have their entire libraries in both formats, while Adobe has but a handful of TrueType fonts. Given the current state of the tools, although a simple conversion would be easy, it would take a concerted effort of many years to convert all the major vendors' font libraries to True-Type if they also wished to enhance the quality.

Translation Memory Technologies

What is Translation Memory (TM) and translation alignment?

Translation Memory is a database containing a set of texts translated into different languages and divided into fragments which are juxtaposed according to their content. That means that fragments of the source text are juxtaposed to the fragments with the similar content translated into another language.

Such texts translated into different languages are called parallel texts (or bilingual texts).

Fragments in which each text is divided are called segments. Segments are usually made of one or more sentences, parts of sentences or word groups, and, in some cases, words.

Juxtaposed parallel texts are called aligned parallel texts.

Thereby the parallel text alignment (or bilingual text alignment) is a juxtaposition of the source and translated texts by segments. Translators usually call this process translation alignment. A Translation Memory database consists of such aligned translations.

Application of Translation Memory technology and computer-aided translation

TM bases are used by translators when working in various computer-aided translation tools (CAT-tools) which allow executing TM base search, finding repeated segments in new texts and replacing them with translations taken from previously translated texts.

In other words, translators, when working with CAT-tools, use them to divide new texts into segments and check if these segments match those stored in translation memories. When a given match percentage is detected, translation variants are displayed. If a source segment fully matches a translated segment in the database (translation memory), the latter can automatically replace the former. New segments can be slightly different from those stored in translation memories. In this case, it is also possible to insert the stored segment into the text, but a translator will have to make necessary changes. Thus, a translator either accepts the suggested variant, or changes and accepts it, or translates the segment as a new one.

Advantages of Using Translation Memory for Clients of Language Service Providers (LSP)

Then making an order, you can provide translation companies with TranslationMemory bases containing translated corporate documentation to:

Save time.

Translators won't have to translate fragments that were already translated once, thus increasing productivity and reducing completion terms.

Reduce costs.

Shorter completion terms and lower labor-intensiveness provide for lower costs.

Maintain company-specific style and terminology.

Translation Memories allow staying in line with terminology accepted in your company. This is especially critical for clients working in specific industry branches and for those who choose to work with multiple translation companies. A common translation database (Translation Memory) ensures uniformity of style and terminology as well as high translation quality.

Advantages of using TM for language service providers, translation agencies, departments and individual translators

Shorter completion terms.

With translations stored in TM bases, translators can save time when working on new texts with similar content. There is no need to translate sections that were already translated once, and search for branch- or company-specific terms. Thus, task completion terms become shorter.

Increased income.

Shorter terms mean better productivity. More orders can be fulfilled within the same time-frame.

Better translation quality.

In addition to increased productivity, Translation Memories help maintain the uniformity of terminology translation. Uniformity is critical when translating specialized texts.

Image of translation expert.

The TM technology is widespread in Europe and the USA, where translators with Translation Memory skills are an industry standard. Professional companies have already adopted it to ensure high quality standards.

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