Digital Fonts

There are two core technologies of digital fonts.

1. PostScript, based on the page description language developed by Adobe (also known as Type 1).

2. TrueType, developed by Apple Computer and Microsoft. To understand these digital fonts we need to review display and printed characters. A Computer Display is a grid of tiny squares called pixels (for picture elements).

The number of screen pixels can vary between 640x480 and 1280x1024 depending on the quality of the monitor and the video driver. The Display is called a bitmap.

A bit (binary digit) is the smallest unit of information used by a computer, has two values 0 or 1 (equivalent logically, on or off). Modern display devices offer bit depths of 8 bits per color for a total of 24 bits at each pixel. Digital output devices are also bitmapped but generally at a much higher resolution than displays.

First Digital Fonts - Bitmaps told the computer which bits (pixels) to turn on and off (1 bit displays). Still used for some screen displays, but have the disadvantage that (like metal type) each point size is a separate font. Because the font is a collection of dots, when it is scaled larger dots are produced and curves appear jagged.

Fonts Defined by curves - Instead of describing characters as a collection of dots, PostScript and TrueType fonts describe each character by a set of mathematical curves. Software called a rasterizer uses the outline information to create the right size of bitmap for the resolution of the output device. This terminology derives from the German word raster, which describes the pattern traversed by the electron beams in a CRT monitor. Rasterizer may be built into the printer such as a PostScript printer. It may run on the computer; Adobe Type Manager rasterizes PostScript fonts for on screen use and for non-PostScript printers. The TrueType rasterizer acts similarly and is included in some PostScript printers.

PostScript Fonts - Consist of two separate files: a bitmapped (screen) font and an outline (printer) font.

TrueType Fonts - Single file with outlines to generate both screen and printer fonts.

Functionality - The two formats are nearly identical. Most fonts available for both.

Character Set - Virtually all computers now use the ASCII (American Standard Code for Information Interchange) which allows 256 characters (8 bits or 1 byte).The first 128 characters are taken by the upper- and lowercase alphanumeric characters and punctuation marks. The remaining 128 characters are platform and font dependant.

New Standard - 256 characters are not always enough. The proposed Unicode standard is based on 16 bit (double-byte) encoding, admitting more than 65,000 characters (essential for non-Roman alphabets).

New flavors of PostScript and TrueType also address this limitation. Fonts compliant with Apple’s TrueType GX format can contain up to 65,000 glyphs (the symbols that represent characters). TrueType GX fonts automatically substitutes the appropriate fraction or ligature for a specific combination of characters. Adobe’s Multiple Master fonts contain more than one master design, e.g. a very wide version and a very narrow version.