March 16, 2006

Smart Unicode typefaces released under free license

Author: Bruce Byfield

SIL International, a non-government organization specializing in linguistics, has released two new typefaces under a free license. The fonts, Charis SIL and Doulos SIL, are early examples of what SIL intends as a new standard for typefaces. Each font includes a broad range of Unicode-based characters and symbols, and is designed for use with so-called smart font technologies.

Charis SIL and Doulos SIL are basic typefaces -- proofs of concept, you might say. Charis SIL is based on Bitstream Charter, one of the first fonts designed for laser printers. The resemblance is so close that Charis SIL includes Charter's license in the copyright notice. It is available in four weights: roman, bold, italic, and bold italic. Similarly, Doulos SIL is designed for compatibility with Times Roman, one of the most widely used serif typefaces. Only a roman weight is included.

The two fonts replace two earlier proprietary fonts with far fewer characters, which were called SIL Charis and SIL Doulos. The naming scheme reversal indicates that the new versions are Unicode-based.

Both typefaces have extensive support for Unicode, the universal encoding table. Charis SIL, for example, includes more than 2,400 characters and symbols, including 1,900 that accord with the Unicode 4.1 standard. Both fonts offer Unicode-based support for Roman and Cyrillic characters, plus extensive sets of characters and symbols intended mainly for linguistics. These additional sets include combined diacritical marks, currency symbols, mathematical operators, and general punctuation, as well as arrows, dingbats, and geometric shapes. Some Greek and Arabic characters are also included. This wide range of characters explain the size of the font files -- both are 1.3 megabytes, more than 15 times the size of the average TrueType-format files.

Another feature of the two fonts is their support for smart font technology. When either font is used in a program that supports OpenType, Apple Advanced Typography, or SIL's Graphite, stacked diacritical marks and ligatures are automatically inserted as appropriate. For example, when one "f" follows another, they will be replaced by a single double-f character without any need to select it from a character map or to use special keystrokes.

So far, only a few programs support any of these smart font technologies; most notably, OpenType is supported by Microsoft Office's Word and Publisher and by 2.0.1. However, such technologies can potentially increase the sophistication of typography in any language. Perhaps even more importantly, these programs promise increased support for non-European languages in computing, allowing them to be input more easily and with greater accuracy.

Both typefaces can be used normally in programs without support for smart font technology as well.

Charis SIL and Doulos SIL are two of the first three typefaces to be released under the SIL Open Font License, which was recently approved by the Free Software Foundation. The source files are not available online right now because SIL is investigating improving its build process, but the FONTLOG.txt that accompanies Charis SIL explains how to contribute to the project.

NewsForge recently reviewed Gentium, the first font released under the Open Font License. Unlike the others, Gentium lacks support for smart font technologies.

Charis SIL and Doulos SIL are more workaday designs than Gentium, which began as an attempt to translate the strokes of calligraphy into a typeface design. However, with their selection of characters and symbols, support for smart font technology, and free license, they illustrate directions in which digital typefaces may be heading.

What's more, with their free license, Charis SIL and Doulos SIL mark an area in which free software is leading the way.

Bruce Byfield is a course designer and instructor, and a computer journalist who writes regularly for NewsForge,, and IT Manager's Journal.


  • Open Source