kern

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Kerning brings A and V closer with their serifs over each other

In typography, kerning (less commonly mortising) is the process of adjusting the spacing between characters in a proportional font, usually to achieve a visually pleasing result. Kerning adjusts the space between individual letter forms, while tracking (letter-spacing) adjusts spacing uniformly over a range of characters.^[1] In a well-kerned font, the two-dimensional blank spaces between each pair of characters all have similar area.

The related term kern denotes a part of a type letter that overhangs the edge of the type block.

In metal typesetting

The glyph on the right is kerned to overlap the succeeding character.

The word kern is a cognate of corner. In the days when all type was cast metal, a corner was notched to a consistent height on one or both sides of a letter-piece. Such notched pieces were only set against one another, not against unnotched ones, which had straight sides. The corner allowed for a character's features to reach into the area normally taken up by the next character, for example the top bar of the T, or the right diagonal stroke of the V to hang over the bottom left corner of an A.

Having a consistently shaped corner cut out allowed for using fewer pieces of type to make up all possible kerning pairs; for example a T- and V-piece with kerning on the right would match the same A piece with a matching kerning indention on the left.

An alternative is to have ligatures for common glyph combinations, such as the French L', or the combinations ff, fi and ffi.

Example

Simple proportional typeface will specify the right and left boundaries, called sidebearings, of each glyph. However, depending on the adjacent letter, the space may be reduced (and occasionally increased) to improve the overall appearance of the text. For example (see above first illustration), A and V can be placed closer together so that the top left of the V is directly above the bottom right of the A.

Kerning perception

Kerning contrasted with tracking (letter-spacing). While tracking adjusts the space between characters evenly, regardless of the characters, kerning adjusts the space based on character pairs. There is strong kerning between the V and the A, and no kerning between the S and the T.

A visually pleasing result, even with no "kerning control", can be achieved with some control of the space between letters.

A webpage concrete example (illustrated below): with CSS1 letter-spacing property you can lost or enhance kerning perception, and into a "letter-spaced text" you can simulate kerning.

Digital typography

Computer fonts and standards, like PostScript fonts, TrueType, OpenType and others, developed in the late 1980s, for digital printers and desktop publishing. Digital typography use in metal typesetting concepts, and the similar goals. In the context of computer fonts, kerning is an important goal.

NOTE: monospaced fonts, like Courier can't use kerning.

Kerning pairs

In digital typography, kerning is usually applied to kerning pairs as a number to be added to the default character spacing, expressed in the font's coordinate system. A digital font's kerning feature can also increase the character spacing between two characters. Increased character width is used mainly in conjunction with accented letters.

Kerning classes

Another approach is to use kerning classes; where one offset is stored for any pair of characters from two sets, for example (V, W) and (a, e, o). This one class is equivalent to the pairs Va, Wa, Ve, We, etc. Kerning classes can be used in OpenType fonts, and applications that support this feature. Although this is the newest, most advanced form of kerning, using kerning classes is essentially the same approach as was used in metal type. The use of kerning classes is necessitated mostly by today's multi-language fonts that feature many more glyphs, and more kerning pairs, than a single language font would need; especially accented letters.

Examples of kerned letters

Kerning is widely used to fit capital letters, such as T, V, W, and Y, closer to some other capital letters on either side (especially A) and to some lower case letters on the right side, such as the combination Ro. It is also used to fit a period (full stop) closer to these and to F, as well as the lower case letters y and r. Some other combinations are AC, FA, and OA.

Which letters need to be kerned depends on the languages the font is to be used with. Some combinations of letters are not used in normal words in any language, so to include kerning for these combinations is not necessary.

Autokerning

Three versions of "WAR" in the Clarendon typeface: The top version has no kerning, the middle version has auto-kerning applied, and the bottom version has manually adjusted kerning.

Some typographic programs provide an autokerning feature. Autokerning simply takes into account a predefined list of common kerning pairs and, if the outlines of two consecutive glyphs are spaced too far apart, makes a kerning entry. Auto kerning is especially useful for kerning multi-language fonts. However, it is rarely a sufficient alternative for manual kerning, as some characters may appear to an algorithmic comparison to be spaced very closely together, but to a human reader might appear to be spaced too far apart; especially when the only part of a glyph that is 'too close' is a diacritic sign.

Uses

Kerning is implicitly part of digital type design, and advanced typographic systems allow the specification of kerning. It is commonly confused with tracking. Most high-quality fonts contain instructions for kerning which are applied automatically by the typesetting engine.

Most typesetting systems, including the freely available TeX and all of its derivative software, support the proper use of kerning. Many word processors, including Microsoft Word, OpenOffice Writer and LibreOffice Writer also support kerning.

Non-proportional (monospaced) fonts don't use kerning, since their characters by definition always have the same spacing.

Kerning tools

Some page layout programs allow the user to kern characters within their text. However, to permanently change the kerning of a font one must use a font editor.

Web standards

The text font properties in a webpage or XML renderization is controled by the CSS standard (a W3C Recommendation).

There are no font-kerning for CSS1 or CSS2. The new specification, CSS3, has not been approved as a standard, but there are a property proposed for font-kerning ^[2] . Only specific fonts, like OpenFonts, have this property, for future use in CSS3 controls.

References

1. ^ "Fonts : Type topics: Glossary". Adobe. http://www.adobe.com/type/topics/glossary.html. Retrieved 2011-09-16. 
2. ^ The font-kerning property in the 2012's CSS3 Draft: http://www.w3.org/TR/css3-fonts/#font-kerning-prop

Look up kerning in Wiktionary, the free dictionary.

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