Trimming Kerning Pairs
Now that one can add loads of kerning pairs by using kerning classes and autokern, fonts tend to get bloated with a lot of pairs that are too small to be worth keeping. For a standard font with 2048 funits per em, a kerning value of less than 10 or 20 is barely noticeable. Fortunately, the OpenType Designer has a way of removing these small values quickly.
- Run Autokern
- Manually check for positive values. There’s no reason not to use positive kerning, but they are often an indicator that side-bearings need some attention.
- Fix the side-bearings then run Autokern again.
- Export the OpenType Layout Definition script from the OpenType Designer to preserve all of the kerning classes and kerning pairs.
- Optionally, remove any unused classes from the Class Manager
- Right-click on the Pair Adjustment lookup, and select Trim
- Select the value that you want to trim. Both positive and negative values. Values equal to or greater than the chosen value will not be trimmed.
In my test, 25,672 pairs were trimmed to 25,379.