Fitting and kerning

The mark, spaced the way a type designer would

What is being set

Fitting / the white each letter carries

White

Depth

Band

Leading

Clearance

Clip the t

Cut the F arm

Overhanging capitals set on the font The colon after Short Justify the four lines The index line underneath

Show

The white between letters Baseline, cap and overshoot

Pairs / kern in units of 1000 em

Kern

Letters are not fitted by the gap between them but by the white each one carries. Every glyph is measured scanline by scanline down its measuring band, the distance from its edge to its ink clamped at the depth you set, and the space between two letters is chosen so the white on both sides of the join adds up to the same amount everywhere. That is the fit. Kerning is then the exception: the pairs that break the rhythm because of what their shapes do — a round against a straight, an open corner, a diagonal. Two measures are at work: the fit uses the mean white each letter carries, and the table measures the corridor actually left between the two shapes. Where the second disagrees with the first by more than 8%, the pair is flagged, and that is a kern waiting to be cut. Even the rhythm does that pass in units of 1000 em; any pair can then be taken by hand. The bars show the result and the squint test shows whether it reads as one even grey.

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