What is the difference between TrueType fonts and Type-1 fonts?

Question

What is the difference between TrueType fonts and Type-1 fonts?

Answer 1

Type-1 is the older format, and dates back to the days when Adobe where pioneering DTP with PostScript and vector fonts. At the time Type 1 and Type 3 were the only formats understood by PostScript printers, and only Type 1 could include hints needed to make fonts look good, and the format was a trade secret. This way Adobe relegated other font foundries to non-hinted fonts using Type 3 format.

TrueType was invented by Microsoft as a way (a) to break Adobe's monopoly on hinted font formats, (b) to avoid using a format associated with the Macintosh and PostScript on Windows. Internally TrueType used quadratic curves rather than cubic beziers, thus making them faster to render on the screen and on the cheaper non-PostScript-capable printeres used on Windows sytems. TrueType also has better support for Unicode and other things invented since the creation of Type 1. Modern Macs support TrueType as well.

The new format OpenType combines TrueType and Type 1 (the vector data is permitted to be in quadratic or cubic form, so you can directly convert either of the old formats to the OpenType). OpenType also has support for fancy automatic ligatures and glyph substitution, which is nice in English text and vital for text using Arabic or Indian scripts.

Answer 2

The Postscript Type-1 specification was created by Adobe back in 1985 or so. Type-1 fonts are vector based. You can find the specification in "Adobe Type 1. Font Format.".

TrueType fonts were defined by Apple a couple of years earlier so True Type and PostScript were competitors in the 1990s. Microsoft picked up True Type for the native Windows font format in the beginning 1990s (for using PostScript, additional tools like Adobe Type manager were necessary).

Today, Microsoft is fading out support for PostScript fonts. Try using one as an UI font in Vista. Good luck ;-)

As a successor of TrueType, Microsoft (I think together with Adobe) created the Open Type (anytime around 2000) format and Adobe converted their whole font library into the new format (you can still get them as Type-1 fonts).

Answer 3

A very key difference is that PostScript (and PostScript flavoured OpenType) supports cubic Bézier curves, where each arc of each glyph is described by four control points. TrueType (and tt flavored OpenType) uses quadratic curves, with each arc having only three control points. This offers less control over the shape of the curve.

Another key difference is the way they perform hinting. Since TrueType was originally targeted to low resolution screen rendering, its hinting system works by adjusting the curves to fit nicely on pixel lattice points, using a fairly elaborate bytecode mechanism. PostScript fonts were intended for higher resolution paper prints, and used guidelines to snap curves to right angles at appropriate places.