Glossary

AFM

(AFM)

Stands for Adobe Font Metric. These files store information about the width and spacing associated with the font, as opposed to information about the font shape.

Anti-Aliasing

Also referred to as font smoothing is a technique used to render fonts on low resolution devices (such as a monitor). The problem with rendering fonts is that the fonts consist of outlines, but the device renders in dots. The obvious way to render a font is to color black any pixel inside the outline, and leave all other dots. The problem with this is that it doesn't adequately address the pixels that are on the outline. A smarter algorithm would be to color the boundary pixels gray. Anti-aliasing essentially involves doing this.

Bitmap Fonts

These fonts are simply a collection of dots. Each character of the font is stored as a dot matrix. Because of this, bitmap fonts are device dependent, so you can't use the same bitmap fonts on a screen and a printer. Examples of bitmap screen fonts include old .pcf and .bdf fonts used by X. Examples of printer bitmap fonts include TeX's PK fonts.

Charset

A group of 8-bit glyphs. For example, the ISO-8859-1 (a.k.a. Latin-1) contain the regular latin chars for west european languages, ISO-8859-8 contain the hebrew chars, ISO-8859-5 have the cyrillic chars, etc. The concept is now obsolete due the advent of Unicode. Linux' base C library (libc) contain the technology to convert text from one charset to another and to/from Unicode.

Dots Per Inch or DPI

(DPI)

Monitors typically display at 75-100 DPI, while modern printers vary from 300-1200 DPI.

Expert Font

Are collections of additional characters that supplement a font. They include small caps fonts, ornaments, extra ligatures, and variable width digits. Many of Adobe's fonts have expert fonts available.

Font Server

A background program that makes fonts available to an X server like X.org or XFree86.

Glyph

A glyph is a fancy word for a shape. It is a component that makes up an outline font. For example, the dot on the letter "i" is a glyph, as is the vertical line, as are the serifs. Glyphs determine the shape of the font.

Kerning

In variable width fonts, different pairs of characters are spaced differently. The font metric files store information regarding spacing between pairs of characters, called kerning pairs.

Ligature

A ligature is a special character that is used to represent a sequence of characters. This is best explained by example -- when the letter "fi" are rendered, the dot on the "i" collides with the "f", and the serif on the top left of the "i" can also collide with the horizontal stroke of the "f". The "fi" ligature is a single character that can be used in the place of a single "f" followed by a single "i". There are also ligatures for "fl", "ffi", and "ffl". Most fonts only include the "fi" and "fl" ligatures. The other ligatures may be made available in an expert font.

Metafont

A graphics language used for creating fonts. Metafont has a lot of nice features, the main one being that fonts created with metafont need not just scale linearly. That is, a 17 point computer modern font generated by metafont is not the same as a magnified 10 point computer modern font. Prior to Adobe's multiple master technology, metafont was unique with respect to having this feature. Metafonts main advantage is that it produces high quality fonts. The disadvantage is that generating bitmaps from the outline fonts is slow, so they aren't feasible for WYSIWYG publishing.

PostScript

(PS)

a programming language designed for page description. PostScript was a trademark of it's inventor, Adobe. However, it is also an ISO standard. Postscript needs an interpreter to render it. This can be done via a program on the computer, such as ghostscript, or it can be interpreted by some printers.

Sans Serif

Fonts without serif (sans is French for ``without''). These fonts have a stark appearance, and are well suited for writing headlines. While textbook typography mandates that serif fonts be used just for headlines, they can have other uses. There are sans serif fonts designed for readability as opposed to impact. Short punchy documents that are skimmed (such as catalogues and marketting brochures) may use them, and recently, Microsoft have made available the Verdana font which is designed for readability at small sizes on low resolution devices. Well known sans serif fonts include Lucida Sans, MS Comic Sans, Avant Garde, Arial, Verdana, Century Gothic.

Serif

Fonts with little hooks (called serifs) on the ends of the font. The serifs usually help make the font more readable. However, serifs are quite difficult to render on low resolution devices, especially at small font sizes (because they are a fine detail), so it is often true that at small sizes on low resolution devices, sans serif fonts (such as Microsoft's Verdana) prove more readable. Another issue is that there are sans serif fonts (like the moderns) that are not designed for writing long documents.

Slab Serif

A certain class of font whose serifs look like slabs (eg: flat lines or blocks) and not hooks. Slab serif fonts are often, but not always very readable. Because the serifs are simple and strong, they give one the feeling that they have been punched into the page. Well known examples of slab serifs are Clarendon, New Century Schoolbook, and Memphis.

Type 1

A type of font designed by Adobe. These fonts are well supported by almost all linux applications, because they have been supported by the X server architecture and the PostScript standard for a long time. Postscript fonts are distributed in many different formats. Typically, a UNIX PostScript font is distributed as an afm (adobe font metric) file, and an outline file, which is usually a .pfb (printer font binary) or .pfa (printer font ascii) file. The outline file contains all the glyphs, while the metric file contains the metrics.

type3

Similar to Type 1. The file extensions are similar to Type 1 fonts (they are distributed as .pfa and afm files), but they are not supported by X, and because of this, there are not very many linux applications which support them.

Unicode

Before the advent of Unicode, each char was represented by a single byte, which let us have a range of 256 chars. The char for hex code 0xe2 in the Latin-1 charset maps to an "â" (circumflex "a"), while in the ISO-8859-7 (greek) charset it maps to the "β" (beta) letter. Unicode introduced multibyte characters with the objective of having each char of every culture and civilization on earth mapping to its unique multibyte hex code. So in our example "â" is 0x00e2 and "β" 0x03b2.

UTF-8

UTF-8 is a Unicode variation that is compatible with the Latin-1 (ISO-8859-1) charset. A UTF-8 .txt file that contain some west european language as english, portuguese or spanish text is byte-identical to its Latin-1 version. If greek, hebrew, japanese or other language text is included in this same .txt file, each of these chars will be multibyte, prefixed by some UTF-8 escaping bytes. Modern applications as OpenOffice.org produce UTF-8 documents. UTF-8 must be the charset of choice when you create plain text, HTML etc files.