This repository hosts material that I am collecting about various approaches to the automation of letterspacing and kerning.
Note that by "collecting," present tense, I subtly indicate that the contents of the repository are not likely, at any arbitrary point in time, to be in a state which one should regard as "complete." Therefore if you notice something I have left out or otherwise missed, please do feel free to drop an angry pull request that adds it or to express your outrage at my shortsightedness through different means.
Classical heuristics have been described by a number of authors, including Walter Tracy and Adrian Frutiger.
The Tracy method defines a small set of spacing values—in a fixed ratio to each other—to be assigned as the left and right sidebearings for most of the Latin uppercase and lowercase letters. The base value from which the other spacing values are derived is taken from the distance between the stems of n and H, so in a small sense it can be said to "automate" spacing decisions.
However, Tracy's approach leaves out several glyphs, which he says "must be spaced visually," and it is limited solely to the basic Latin alphabet, as well as assuming an upright Roman form with serifs and traditonal dimensions.
Adrian Frutiger was said to use a similar systematic approach to spacing, although he made only a few comments about his method.
Tracy's approach was used by Hermann Zapf to develop the automatic spacing functionality later found in several Adobe applications.
The wedge method developed by David Kindersley sought to find the "optical center" of each glyph—that is, horizontal point at which a vertical line drawn through the glyph produces an equal "gray ratio" (that is, percentage of black) on each side.
LetterModel is an approach to letterspacing developed by Frank E. Blokland, and based on the notion that early miniscules were drawn on a (relatively large-scale, with respect to letter size) regular grid system.
AutoSpace by Andres Torresi of Huerta Tipográfica is an add-on for the Glyphs font editor. It has been demonstrated in several widely shared online videos, but has not yet been formally released.
Pablo Impallari's Spacing Macro is a macro for FontLab. It was initially inspired by Frank E. Blokland's LetterModel.
Kernagic by Øyvind Kolås is a standalone software tool that can automatically letterspace a UFO font. It implements several different letterspacing approaches
Typefacet Autokern is a Python program by Charles M. Chen that can automatically adjust side-bearings of kerning pairs in a font based on a set of user-supplied general arguments.
BubbleKern is an add-on for the Glyphs font editor.
iKern by Igino Marini is a software service; Marini describes the theory behind his approach, but the specific algorithms at the heart of the method employed have not been published.
KernMaster is a component of the FontMaster application suite, published by Dutch Type Library.
LightMeter is a RoboFont utility that calculates the "grayness" percentage of a glyph or any subselection of a glyph. That is, it computes the ratio of black to total area for the region of interest.
FittingRoom is a letter-fitting utility that works by analyzing a set of glyphs and breaking the set into classes, where each class has a similar enough shape that it can be spaced using the same means.