排版印刷

字距调整

为视觉美观而调整特定字符对（如AV、To、LT）之间间距的操作，是字体特性而非Unicode概念，但会影响Unicode文本的渲染。

2023-06-26 · Updated 2025-01-14

What is Kerning?

Kerning is the typographic process of adjusting the horizontal spacing between specific pairs of characters to achieve visually consistent spacing. Unlike tracking (which adjusts spacing uniformly across all characters) or word spacing, kerning is targeted — it corrects for the optical illusion that certain character combinations appear to have more or less space between them than they actually do.

The classic example is "AV": the diagonal strokes of A and V create a large visual gap when they sit at their default spacing, even though no extra space was added. Kerning pulls them closer together so the gap looks similar to the spacing between, say, "nn."

Why Kerning is Necessary

Characters are designed in isolation but read in combination. A letter's bounding box (the rectangle enclosing its glyph) doesn't account for the white space created by its specific shape. Pairs that frequently require kerning include:

Pair	Problem	Solution
AV	A's right diagonal + V's left diagonal create gap	Reduce space
To	T's horizontal arm overhangs lowercase letters	Reduce space
LT	L's wide base + T's serif/stem create gap	Reduce space
ff	f hooks can collide	Increase or use ligature
r.	r's arm leaves gap before period	Reduce space

Font Kerning Tables

Professional fonts include kern tables (or the more modern GPOS table in OpenType) that specify adjustments for hundreds or thousands of character pairs. A typical professional typeface might contain 5,000–20,000 kern pairs.

The adjustment is measured in font units (usually 1/1000 or 1/2048 of an em). Negative values bring characters closer; positive values push them apart.

Kerning vs. Tracking vs. Leading

Term	Scope	Purpose
Kerning	Between specific character pairs	Correct optical unevenness
Tracking (letter-spacing)	Uniform across all characters	Stylistic spacing adjustment
Word spacing	Between words	Justify text, improve readability
Leading (line-height)	Between lines	Vertical rhythm and readability

Kerning in Practice

CSS provides two mechanisms:

/* Enable font's built-in kerning tables (recommended) */
p {
  font-kerning: normal; /* default in modern browsers */
}

/* Disable kerning */
p {
  font-kerning: none;
}

/* Manual letter-spacing (tracking, not true kerning) */
h1 {
  letter-spacing: 0.05em;
}

Manual kerning in design tools like Adobe Illustrator or InDesign: place the cursor between two characters, then use Alt/Option + Arrow keys to adjust. InDesign shows the kern value in the Character panel.

Optical vs. Metric Kerning

Most professional design software offers two kerning modes: - Metric kerning: uses the kern pairs built into the font file (fastest, most consistent) - Optical kerning: software analyzes the actual glyph shapes and calculates spacing algorithmically (better for fonts with sparse kern tables, especially display sizes)

Quick Facts

Property	Value
Definition	Spacing adjustment between specific character pairs
Measured in	Font units (per-em fractions) or points
OpenType table	`GPOS` (newer), `kern` (legacy)
CSS property	`font-kerning: normal / none / auto`
Common bad kern pairs	AV, AW, AT, WA, To, Tr, Ta, Ve, Vo, LT, PA
Design tool shortcut (Mac)	Option + Left/Right Arrow
Design tool shortcut (Win)	Alt + Left/Right Arrow