TrueType overview

TrueType is a digital font technology designed by Apple Computer, and now used by both Apple and Microsoft in their operating systems. Microsoft has distributed millions of quality TrueType fonts in hundreds of different styles, including them in its range of products and the popular TrueType Font Packs.

TrueType fonts offer the highest possible quality on computer screens and printers, and include a range of features which make them easy to use.

The history of TrueType's development is discussed briefly in our History of TrueType document, which explains the various incarnations of the technology, as well as some of the reasons TrueType exists at all.

What do I need in order to use TrueType?

The TrueType font technology consists of two components: the TrueType fonts themselves, which come in many thousands of different styles, and can be purchased individually or in collections from font manufacturers; and the TrueType rasterizer, a piece of software built into System 7.x on the Apple Macintosh range of computers, and also into Microsoft's Windows family of operating systems.

Both components - the font and the rasterizer, are necessary to display and print TrueType fonts on a computer system. It is the interaction between the TrueType fonts, the TrueType rasterizer and the software program in which the TrueType font is used that determines the appearance of the letterforms in the font.

Where can I get TrueType from?

If you're using a Mac or a Windows machine, the chances are that you're already using the TrueType rasterizer and the TrueType fonts both Apple and Microsoft include with the basic operating system.

If you're using Apple Macintosh or Windows based computers, all you need to do is purchase the fonts you want to use.

The TrueType rasterizer

The TrueType font technology consists of two parts: the description of the fonts themselves (the TrueType font files), and the program which reads the font description and generates the bitmaps (the TrueType Rasterizer).

The TrueType Rasterizer is a computer program which is typically incorporated as part of an operating system or printer control software. With this in mind, it has been written with a well defined client interface, and a clean modular structure in portable C.

The job of the TrueType Rasterizer is to generate character bitmaps for screens and printers (otherwise known as raster devices). It accomplishes this by performing the following tasks:

• Reading the outline description of the character (lines and splines) from the TrueType font file.
• Scaling the outline description of the character to the requested size and device resolution.
• Adjusting the outline description to the pixel grid (based on hinting information).
• Filling the adjusted outline with pixels (scan conversion).

What's in a TrueType font?

A digital font contains much more than just the characters associated with a given alphabet or script. A TrueType font file includes many different kinds of information used by the TrueType rasterizer and the operating system software to ensure that characters display on the computer screen or print out exactly as the font designer intended them to. All of the information in a TrueType font is arranged in a series of tables. For technical information about these tables, you can see our TrueType specification.

In addition to the shapes of each character, a TrueType font includes information about how the characters should be spaced vertically and horizontally within a block of text, character mapping details (governing the variety of characters included in the font and the keystrokes needed to access them), and much more besides. The fonts also include manufacturer's details, such as copyrights, names and licensing permissions.

Description of characters

One of the more obvious things TrueType fonts include is the shape of each character. Each and every letterform contained in a TrueType font is stored as an outline, or more accurately, as a mathematical description of the character constructed from a series of points. For this reason, TrueType is known as an outline font format.

Probably the greatest thing about storing characters as outlines is that only one outline per character is needed to produce all the sizes of that character you'll ever need. A single outline can be scaled to an enormous range of different sizes, some of which are illustrated below. This enables the same character to be displayed on monitors of different resolutions, and to be printed out at a large number of different sizes.To scale a character outline is a simple mathematical operation, as indeed are other transformations such as rotation and reflections.

The user never actually sees the outlines stored in an outline font, because before a character can be displayed on the screen or the printer, a bitmap has to be produced, by the TrueType rasterizer. This is because screen displays and printers both use dot patterns to represent images (sufficiently magnify any screen image or print-out, and you'll notice the pixel pattern). The character outlines contained in the TrueType font are scaled to the requested size, and are converted into bitmaps by turning on the pixels encompassed by the outline. This process is known as scan conversion or rasterization.

Character sets and mapping

TrueType fonts also contain character maps - information concerning the types and quantity of characters included in the font, and details as to how these characters are accessed from the keyboard.

TrueType fonts on the PC and the Mac

Although TrueType fonts can be used on both the Macintosh and Windows platforms, slight differences in the way each operating system handles the fonts lead vendors to produce separate versions of the font for each platform. Some vendors will provide you with both Mac and Windows format TrueType files, while others may treat them as different products. Contact individual vendors for specific details.

This oddity arises because of the different file system used on the two platforms. Information can be included in the font to determine whether the font can be used on both kinds of system, or one or the other.

On a Macintosh, the TrueType font file is sometimes referred to as an SFNT and, under Windows as a .TTF. The information contained in the fonts is the same, and making the necessary adjustments to allow the font to run on both platforms is a relatively straightforward task.