ot2kpx (1) - Linux Man Pages

ot2kpx: extract kerning information from OpenType fonts


ot2kpx - extract kerning information from OpenType fonts


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.


Print a short help text and exit.
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.
Output the kerning data as a Luatex custom font feature, to be included in a "\directlua" command.
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 [at] gmail.com>


Copyright (C) 2005-2020 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 20200129.


(See the source code for the rest of the story.)
Added the -version option.
Added the -lua command-line option to get output in Luatex's custom feature format.