---
name: "ot2kpx"
section: "1"
platform: "linux"
package: "texlive-doc"
version: "2026.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ot2kpx"
---

# ot2kpx(1)

extract kerning information from OpenType fonts

## NAME

ot2kpx - extract kerning information from OpenType fonts

## SYNOPSIS

**ot2kpx** \[ *-afm* \| *-kpx* \| *-lua* \] **\<fontfile\>**

## DESCRIPTION

**ot2kpx** extract the kerning data from OpenType fonts and prints it to `"stdout"`, either in Adobe's KPX format (for adding to an *afm* file) or as a Luatex custom feature, for use with the `"\directlua"` command.

## OPTIONS AND ARGUMENTS

- **-help**

  Print a short help text and exit.

- **-version**

  Print **ot2kpx**'s version and exit.

- **-afm**, **-kpx**

  Output the kerning data in Adobe's KPX format, as used in *afm* files. This is the default output format.

- **-lua**

  Output the kerning data as a Luatex custom font feature, to be included in a `"\directlua"` command.

- **\<fontfile\>**

  The OpenType font (both *otf* and *ttf* format are supported).

## RESTRICTIONS

- **-**

  **ot2kpx** doesn't implement all of the OpenType specification. Things that are missing include: support for font files containing multiple fonts, LookupTables with LookupTypes other than 2, "kern" tables with format other than 0 and ValueRecords with other types of data than just XAdvance data.

  Most of these limitations won't matter, since the missing features are rare (the only fonts I know of that use them are the non-western fonts that come with Adobe Reader). Furthermore, many of these features define (according to the OpenType specification) *"subtle, device-dependent* *adjustments at specific font sizes or device resolutions"*; since there's no way to express such adjustments in *afm* format, ignoring them seems to be the only option anyway.

- **-**

  **ot2kpx** collects kerning data first from the "kern" table, then from all LookupTables associated with the "kern" feature; if a kerning pair occurs multiple times, the first value seen is chosen. There are (or may be) several issues with this approach:

  - \-

    The OpenType specification says that fonts in *otf* format shouldn't use the "kern" table at all, just the lookups from the "GPOS" table. Many such fonts do, however, contain a "kern" table, but no "GPOS" table; so we use the "kern" table anyway.

  - \-

    Instead of reading all LookupTables, it might be better to let the user specify a script and language and process only the LookupTables for those values. However, at least in the fonts I checked, all script/language combinations eventually point to the *same* "kern" LookupTables, so this approach wouldn't make any difference (apart from further complicating the code).

## AUTHOR

Marc Penninga \<marcpenninga@gmail.com\>

## COPYRIGHT

Copyright (C) 2005-2026 Marc Penninga.

## LICENSE

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version. A copy of the GNU General Public License is included with **ot2kpx**; see the file *GPLv2.txt*.

## DISCLAIMER

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

## VERSION

This document describes **ot2kpx** version 20260210.

## RECENT CHANGES

(See the source code for the rest of the story.)

- *2019-05-20*

  Added the *-version* option.

- *2019-04-15*

  Added the *-lua* command-line option to get output in Luatex's custom feature format.