ot2kpx - Man Page

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

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.

-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).

• 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).

Marc Penninga <marcpenninga@gmail.com>

Copyright (C) 2005-2023 Marc Penninga.

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.

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.

This document describes ot2kpx version 20230201.

(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.