ot2kpx(1) extract kerning information from OpenType fonts




ot2kpx extract the kerning data from OpenType fonts (both otf and ttf formats) and prints it (in afm format) to "stdout".


The OpenType font (in either otf or ttf format).


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 <[email protected]>


Copyright (C) 2005-2013 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.


(See the source code for the rest of the story.)
Replaced all "given/when" constructions in the source code by "if"'s, to avoid warnings about experimental features in Perl 5.18 and later.
Refactored the code, and fixed a number of bugs in the process. Updated the documentation.