A brief overview of current font technology

Bitmap fonts draw a picture of each glyph by colouring in appropriate pixels in a rectangular grid. By contrast, outline fonts such as Postscript, TrueType and OpenType fonts, describe the outline of the glyph, and then fill in the interior via a process called rasterizing. A third type of font is a stroked font, where each stem of a character is represented by a line through the centre of the stem; the line being rendered later with a certain width.

The principal failing of bitmap fonts is that they do not scale well in size. As the shape of the glyph really consists of rectangular pixels, a significant increase in the size of the font results in this granularity becoming visible as jaggedness in the outline of the characters. Thus, the font designer is forced to create a series of fonts at each of several different sizes. However, such fonts are well-suited for most computer display systems and are still widely used there.

Postscript fonts mathematically describe the outline of the glyph, and are typically used to print with laser printers. Such fonts can be scaled to an arbitrary size, and are usually supplied in different weights and styles, e.g., Roman, bold, italic, etc. Postscript fonts were later enhanced by techniques like hinting, where the outline of a glyph is algorithmically fitted into the available pixel-spacing so as to give the most pleasing shape. Likewise, font metric files are used to supply additional information regarding the font's line breaks and spacing, as well as kerning tables and character-width information.

TrueType fonts were developed by Apple as a replacement for Postscript. They use splines to mathematically describe the outline shape, and include both the mathematical description of the glyphs as well as the bit-mapped display font in a single file.

OpenType [6,7] fonts are the latest font-scaling system developed jointly by Adobe and Microsoft, and also supported on newer Apple computers. OpenType is an amalgamation of features from Postscript and TrueType, and will hopefully eliminate the font-type wars. The possibility of defining rules for complex glyphs or combinations of different glyphs afforded by OpenType makes it the best current solution for Indian language fonts. Microsoft offers a list of frequently asked questions about OpenType [8], detailed OpenType specifications [7], as well as an in-depth article on the subject of the support and development of fonts for Indian languages [9]. A detailed list of OpenType fonts and software is offered by Luc Devroye [10]