TrueType is the popular font format developed by Apple around 1990, subsequently licensed by Microsoft.
TrueType is a very popular format for computer fonts. Not only are system fonts (those included when you buy a new computer) usually in TrueType format, but it is also the most common format of fonts added to computers later – whether those are free fonts or fonts sold commercially.
The format was developed around 1990 by Apple, largely by one man, Sampo Kaasila. It was licensed by Microsoft shortly afterwards. Both companies wanted a font format that was independent of Adobe, whose PostScript Type 1 format was the other main option for them. Still today, one usually gets the choice of TrueType or PostScript when buying fonts.
Both TrueType and Type 1 are scalable font formats. Letter-shapes are defined in terms of the mathematical formulae – based around the idea of “control points” – that define their outlines. Operating systems such as Microsoft Windows and Mac OS X include font rasterizers which, when a program needs a particular font at a certain size, process these formulae to give a bitmap result – a rectangular grid of pixels. The program then displays those pixels on the screen, or sends them to the printer. The formulae produce smooth results at any size, so there’s no limit to how large you can make these fonts; the fonts also work better and better, given more resolution on a printer.
Scalable fonts don’t solve all problems with digital fonts. One important problem, that PostScript Type 1 never fully cracked, is that of very small fonts on low resolution screens. What happens when you have to display text in a space just 9 pixels high? It’s an important question, since so much of the text we read on our screens (resolution: about 100 pixels per inch) is at just those sizes. Without help, scalable fonts produce an illegible mess. The problems of ugliness and illegibility persist to some extent up to much higher sizes and even to printouts on medium quality printers, but they are most acute at the small pixel sizes.
The TrueType approach is not to entrust the rasterizer with choices of aesthetics and legibilty. Instead, those decisions are handed over to the font makers. An entire programming language is made available, so that font engineers can place programs which take the correct pixel decisions, right inside each character in the font. Effectively, every time you type a letter with a TrueType font, a little program runs, measuring various distances in that letter, comparing them with stored values, and so on; and on the basis of that, the outline gets pushed and pulled around. Finally, the distorted outline (which would look awful if ever printed out!) is sent to the rasterizer for filling in with pixels.
The general term for this tweaking of pixels is “hinting”, the same name Adobe use for their technique – which is less predictable and does not rely on programming.
It is difficult to write TrueType hinting programs, and therefore most TrueType fonts on the market today have not had their hinting programs written by people. Instead they are “auto-hinted” by programs such as FontLab and Fontographer. While this often produces acceptable results, these fonts are inferior for intensive reading (such as on websites), for intensive text editing, and for small text labels on website buttons.
All that said, the requirement to add this extra complexity to a font is receding all the time. Modern operating systems use anti-aliasing and enhancements such as ClearType that tune the signal to each of the red, green and blue channels on LCD screens; this makes all fonts much more legible on screen.
As well as the operating system companies, Apple and Microsoft, there have been other foundries have made the leap to writing these font programs properly. They include: