Using Kerning Classes»

Some glyphs often have very similar elements on one or both sides. Consider for example the left sides of “OCGQ”, or both sides of “AĀÁÄÔ. It seems natural to group such similar glyphs into glyph classes and then define kerning between these classes, instead of solely kerning individual pairs. This approach is called class kerning and can dramatically decrease the number of individual kerning pairs a designer needs to define.

FontLab allows you to kern between two glyphs, a glyph and a class (or a class and a glyph), or between two classes. If a glyph is a member of a defined class, and you kern with that glyph, FontLab assumes you want to kern the class unless you tell it otherwise. So the class kerning got the higher priority in FontLab VI.

Defining a Kerning Class»

To create a kerning class:

  1. Open the Classes panel.
  2. Click on the + button below the list of classes and choose Add 1st Kerning Class. (1st means “left” in the scripts with left-to-right writing). You will see a default class name appears in the list of classes and in the Name field: kl
  3. Now drag-drop glyphs from the Font window to the Table area of the panel to add them to the class.
  4. To rename the class, use the class Name field and change kl to kl_A. Click somewhere to apply changes. You finished defining the kerning class and your Classes panel should now look something like this:

Defining a Class Kerning Pair»

Suppose you defined two kerning classes in the Classes panel, 1st (left) class kl_A and 2d (right) class kr_T:

@kl_A = [A Agrave Aacute Acircumflex Atilde Adieresis Aring Amacron Abreve Aogonek];
@kr_T = [T Tcaron Tcommaaccent T_h T_h.commaaccent T_h.caron];

Now you can kern them.

To add the kerning pair:

  1. Select the Text tool and type AT in the Glyph window.
  2. Select the Kerning tool and open the Kerning panel (Window > Panels > Kerning)
  3. Move T closer to A using the mouse. As soon as you release the mouse button, the new class kerning pair will appear in the Kerning panel:

Building OpenType Kerning Feature»

After you defined kerning for all your classes you need to create/update your ‘kern’ feature.

To build or replace the ‘kern’ feature using current classes and kerning info:

  1. Open the Features panel ((Window > Panels > Features)
  2. In the panel’s “hamburger” menu, select Create [kern] feature.
  3. Click on Compile triangle button and preview your kerning working in the Glyph window or the Preview panel.

For general information on kerning, see Kerning, for details on how to do class and regular kerning, see Editing Kerning, Classes panel for more information on classes and how to create them, and Kerning panel for the panel that displays all kerning pairs in the font.

How class kerning is handled at font generation time:

  • If you generate PostScript Type 1 fonts, class-based kerning will be converted (expanded) to plain pair kerning during font generation.
  • In OpenType (PS and TT) fonts, class kerning may be exported directly. It will be directly supported by most modern applications. But names of classes are not preserved so you may find them renamed on import.
  • In addition, if someone uses OpenType PS fonts with class kerning on very old operating systems, the Adobe system font rasterizer (ATM) on Windows and Mac OS is used to automatically convert the Western European subset of the class-based kerning included in the font into plain (“flat”) kerning when the font was installed on classic Mac OS and Windows 2000. This does not happen with recent operating systems such as Mac OS X and later versions of Windows.