[OpenType] Kerning

[Levantovsky, Vladimir]

Thank you, Michelle.

All,

Currently, there is a language in the ISO/IEC 14496-22/DCOR1 (draft corrigendum) that modifies ‘kern’ table section of the “Recommendations” (chapter 7) by adding the following:

When a kern table and GPOS table are both present in a font, and an OFF layout engine is requested to apply kerning to a run of text of a particular script and language system: (a) If the number of kern feature lookups in the resolved language system in the GPOS table is zero, then the kern table must be applied, followed by any remaining GPOS features requested. (b) If the number of kern feature lookups in the resolved language system in the GPOS table is non-zero, then all GPOS lookups, including the kern lookups, must be applied in the usual way and the kern table data ignored.
If a kern table but no GPOS table is present in the font, then an OFF layout engine must apply the kern table to the text, regardless of the resolved language system of the text.
If compatibility with legacy environments is not a concern, font vendors are encouraged to record kerning in the GPOS table's kern feature and not in the kern table.

If we want to modify the text of the corrigendum, we need to come up with and agree on the new wording. The draft corrigendum is currently under open ballot, and in order to submit ballot comments on time we need to finalize any changes to the text no later than end of March.

Thank you and best regards,
Vladimir


From: mpeg-OTspec at yahoogroups.com [mailto:mpeg-OTspec at yahoogroups.com] On Behalf Of Michelle Perham
Sent: Wednesday, March 10, 2010 2:32 PM
To: mpeg-OTspec at yahoogroups.com
Subject: [mpeg-OTspec] FW: [OpenType] Kerning



Forwarding Simon's response posted to the other list.

-----Original Message-----
From: listmaster at indx.co.uk<mailto:listmaster%40indx.co.uk> [mailto:listmaster at indx.co.uk<mailto:listmaster%40indx.co.uk>] On Behalf Of Simon Daniels
Sent: Wednesday, March 10, 2010 10:58 AM
To: multiple recipients of OpenType - sent by
Subject: [OpenType] Kerning

Message from OpenType list:


Hi,

Responding to earlier questions regarding OpenType Kerning and TrueType kern table co-existing in some of our fonts.

There are two reasons some of our fonts contain both styles of kerning…

1. During the development of Office 2007 we made the case for PowerPoint turning on kerning by default. When they followed our advice they found that the new C* fonts were not kerning, we knew we really had to do something, and that was adding in the kern table. This happened at the last minute during Windows Vista/Office 2007, by converting OT-kerning to kern and removing all pairs that contained unmapped glyphs.

2. Some Windows apps, and Mac OS, assumed that any font with GPOS table would contain OpenType kerning, so kern table was being ignored in fonts like TNR which had mark positioning. For this reason we had to add OpenType kerning to some of the legacy fonts which we’d licensed to Apple as well as those commonly used in the OT-savvy Windows apps.

I don’t know if the spec needs to talk about what to do if a font contains both. One would expect that both sets are compatible, and that the app would use the OpenType kerning first, and only use kern if there were no GPOS kerning.

Cheers, Si




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