Multiple Master FontsMultiple master fonts are Type 1 font programs that include two or more "master" fonts within a single font file. It allows users to interpolate many intermediate "instances" of the typeface. The fonts have one or more "axes" which might typically represent the weight, width, or optical size of the font. Thus the user can generate a very large number of variations from a single font - thus providing unprecedented flexibility.
The specifications for the multiple master font format are contained in Adobe Technical Note #5015, Type 1 Font Format Supplement (PDF: 187 KB). Much of the format's potential and the related design issues are discussed in Adobe Technical Note #5091: Designing Multiple Master Typefaces (PDF: 3.7 MB). For options on downloading this large document (click here).
The Weight and Width Axes
The following diagram shows the basic concept - in this example, the Myriad multiple master font contains four master fonts - which are shown in the four corners of the design space (i.e. the charcters which are in outline form). The MyriadMM font has two design axes, weight and width. The solid black characters show just some of the intermediate "instances" that the user can produce by interpolation.
The Optical Size Axis
Multiple master fonts with an optical size axis offer the potential of the highest quality digital type available today. In the days of metal type, master designers and punchcutters would subtlely alter the design of each character to optimize its legibility for the exact size of the final printed letters. With the advent of scalable outline fonts, this capability was all but lost until the introduction of multiple master fonts.
The diagram below shows an example of the subtle differences between two master designs for the Adobe MinionMM font which features an optical size axis. The top example was designed for optimal readability when printed at 6-point; the bottom example is optimized for printing at 72-point. Simple interpolation between these two masters would yield better results than simple linear scaling of a single master, but it would not give the best results. The multiple master format allows the designer to provide a piecewise-linear mapping between the Optical Size coordinates and the point size selected by the user. The result is that the format provides the potential for duplicating the best optical compensations accomplished by the best type designers and punchcutters.
While some multiple master fonts feature three or four axes, multiple master fonts can be very effective with only one or two axes. They might utilize weight axis for a display face, or just an optical size axis for a text font. Using only a single axis greatly simplifies the task of developing a multiple master font.
Multiple Master Font Format Extensions
Two newer multiple master fonts, Adobe Jenson and Adobe Kepler utilize an extension to the multiple master format, and both require the latest versions of ATM software (3.9 for the Macintosh; 4.0 for Windows) and the PostScript driver to be able to work. Adobe Jenson contains intermediate master designs, and Adobe Kepler introduces a non-linear design space feature to help adjust the thick/thin contrast of the strokes in some parts of the design space. These added features are controlled by using PostScript-language code in the procedures in the font that control the conversion back and forth between the design space and user coordinates. This also means that the correct metrics for those fonts can only be derived by correct interpretation of the PostScript language code, and not by linear interpolation of the metrics of the master designs.
Multiple Master Font Development Tools
Font editing tools that support the creation of multiple master fonts include FontLab (available for Windows and Macintosh) from Pyrus North America.