[mpeg-OTspec] AHG on Open Font Format kick-off

Fri Sep 5 21:24:09 CEST 2008

Dear Vladimir Levantovsky,

Great thank you for quick reply.

On Fri, 5 Sep 2008 14:54:46 -0400
"Levantovsky, Vladimir" <Vladimir.Levantovsky at MonotypeImaging.com> wrote:
>I will edit the header title for 'kern' table as you suggested.

Thank you!

>The "Recommendation" section (I believe this is what you were referring
>to as "cross-platform notes") has not been dropped. The whole section is
>in the text of the ISO/IEC 14496-22, clause 6 "Recommendations" (you can
>find comments specific to 'kern' table on page 365 of the current draft
>FCD, and comments on 'cmap' table on page 364).

I'm quite sorry that my previous message lacked the exact
reference. The "cross-platform notes" I mentioned was the
beginning of kern table description in OpenType spec, here
I quote:

http://www.microsoft.com/typography/otspec/kern.htm

	kern - Kerning

	NOTE: Apple has extended the definition of the 'kern'
	table to provide additional functionality.
	The Apple extensions are not supported on Windows.
	Fonts intended for cross-platform use or for the Windows
	platform in general should conform to the 'kern' table
	format specified here.

I think this note is not included in ISO/IEC 14496-22.
The recommendation for kern table describes how to make
a kern table working on Windows, but does not mention
about Apple platform.

>As far as 'kern' table and subtable version numbers and field
>definitions are concerned - the current text is identical to original
>text of OpenType specification 1.4 and 1.5. I f you believe it would be
>beneficial to modify / update the field descriptions - we would need to
>discuss and approve these changes as part of the established ISO ballot
>process. AHG can not make these decision on its own, without having it
>discussed and approved by the SC29/WG11. I would encourage you to submit
>your comments and proposals as FCD ballot National Body comments.

OK, the compatibility between ISO/IEC 14496-22 and
OpenType spec would be most prioritized task, I understand.
Fortunately, this is the compatibility issue with discouranged
legacy implementation and the urgent standardization is not essential
(Apple 16bit kern is already discouraged in Apple TrueType spec).
I will try to discuss with Apple engineers and propose the change
of OpenType spec 1.7 or later (if Apple engineers think it's
important).

Thank you very much,
mpsuzuki

>
>	From: mpeg-OTspec at yahoogroups.com
>[mailto:mpeg-OTspec at yahoogroups.com] On Behalf Of
>mpsuzuki at hiroshima-u.ac.jp
>	Sent: Friday, September 05, 2008 2:23 PM
>	To: Levantovsky, Vladimir
>	Cc: mihill at microsoft.com; mpeg-OTspec at yahoogroups.com
>	Subject: Re: [mpeg-OTspec] AHG on Open Font Format kick-off
>	
>	
>
>	Dear Vladimir Levantovsky,
>	
>	I'm quite sorry for writing the comment on 2nd FCD in the
>	near of deadline.
>	
>	Recently I've discussed about the implementation of "kern"
>	table with Joshua Hadley, in OpenType mailing list, and
>	read the corresponding parts of existing specifications.
>	Then, I find that I should comment a few points.
>	
>	Editiorial comment
>	------------------
>	
>	In Contents page iv, the most titles of the sections for
>	OFF tables are in the style like "cmap - Character to Glyph
>	Index Mapping Table". But the title of the section for
>	kern table is just "Kerning". I think "kern - Kerning"
>	is compatible with other titles, and compatible with
>	OpenType spec
>(http://www.microsoft.com/typography/otspec/kern.htm
><http://www.microsoft.com/typography/otspec/kern.htm> )
>	
>	non-Editiorial comment (maybe)
>	------------------------------
>	
>	Although ISO/IEC 14496-22 doesn't mention about how to design
>	a cross-platform kern table, the existing specifications of
>	Apple TrueType GX, Microsoft TrueType, and OpenType note
>	about how to make a cross-platform kern table. Yet I've not
>	tracked the reason why the cross-platform notes is dropped
>	in ISO/IEC 14496-22.
>	
>	If ISO/IEC JTC1/SC29/WG11 experts discussed and concluded
>	as it should be removed due to unavoidable incompatibilities,
>	the discussion is worthful, I wish it should be commented
>	in ISO/IEC 14496-22 (even if it's out of main sections).
>	
>	In addition, there is an important note for kern table in
>	the recommendation: Microsoft Windows uses only the first
>	subtable in format 0, for horizontal/no cross-stream/no
>	override. I wish if it's so important and should be moved
>	to or repeated in the main section for kerning table.
>	It is possible for a careful reader to recognize that
>	the subtable format 2 is not supported by Windows nor OS/2,
>	but it is difficult to recognize that multiple subtable
>	is not supported by Windows.
>	
>	# In the case of cmap table, the information "how to
>	# implement cmap table including UCS-4 characters" is
>	# written in the subsection for cmap subtable format 12
>	# and repeated in the recommendation.
>	
>	Also, a few definitions of the elements are slightly unclear.
>	
>	"version" element in the head of kern table:
>	This element is described as "starts at 0".
>	At present, there's no description about the
>	number of version for "kern" table, I think
>	"Set to 0" is better. Why? Although it is out
>	of the scope of OpenType specification, Microsoft
>	platform seems to ignore this element at all and
>	Apple platform seems to distinguish original
>	16bit kern versus 32bit TrueType GX kern.
>	To disambiguify, giving only version 0 is better.
>	I wish if version 1 is described as reserved
>	(as kern subtable format number 1 and 3 are
>	described as "reserved for future use").
>	
>	"version" element in the head of kern sub table:
>	This element is described as "Kern subtable
>	version number". Although it seems that most
>	TrueType fonts set this element to 0, Microsoft
>	and Apple platforms seem to ignore this element.
>	If the neglect of this element is not essential,
>	I wish if the standard value is defined, or,
>	described as this is not used (or renamed as
>	reserved).
>	
>	In addition, I want to hear the comment from Apple, if they
>	are interested in the standardization how to distinguish
>	the coverage element in kern subtable. The bitwise
>interpretation
>	of the coverage element is incompatible between Microsoft
>	TrueType (and OpenType) and Apple TrueType. If any restriction
>	makes it possible to distinguish OpenType 16bit kern from
>	Apple TrueType 16bit kern, I wish if it's addded in future
>	OpenType specification.
>	
>	It seems that current Mac OS X automatically detects OpenType
>	16bit kern and parses it in OpenType syntax, but sometimes
>	the detection is confused. I have a few commercial fonts
>	designed for Microsoft Windows: they are kerned in Windows but
>	not kerned in Mac OS X.
>	
>	When I and Masatake Yamato (Red Hat) implemented a validator
>	of kern table, we took a heuristic algorithm in following:
>	
>	step1:
>	extract 4bit from LSB of coverage element and
>	interpret it as the subtable format as Apple
>	16bit kern.
>	
>	step2:
>	If the subtable format is 0 or 2 and requires
>	the state machine of TrueType GX, the subtable
>	is recognized as of Apple 16bit kern.
>	If it is 1 or 3, TrueType GX state machine is
>	required, so the interpretation is assumed to
>	be wrong - go to step 3.
>	
>	step3:
>	extract 8bit from MSB of coverage element and
>	interpret it as the subtable format as OpenType
>	16bit kern.
>	
>	This algorithm is not perfect. For example, the coverage
>	element for vertical format 0 in Apple 16bit kern would
>	be 0x8000. This is same with the most popular coverage
>	element in OpenType 16bit kern (horizontal format 0).
>	
>	Regards,
>	mpsuzuki
>	
>	On Thu, 14 Aug 2008 16:29:21 -0400
>	"Levantovsky, Vladimir"
><vladimir.levantovsky at monotypeimaging.com
><mailto:vladimir.levantovsky%40monotypeimaging.com> > wrote:
>	>The new version of the draft has been uploaded to AHG files
>storage and
>	>can be downloaded using the following link:
>	
>>http://groups.yahoo.com/group/mpeg-OTspec/files/20080814-w10068_14496-2
>2
><http://groups.yahoo.com/group/mpeg-OTspec/files/20080814-w10068_14496-2
>2> 
>	>_FCD_2nd-Ed.zip
>	
>><http://groups.yahoo.com/group/mpeg-OTspec/files/20080814-w10068_14496-
>2
><http://groups.yahoo.com/group/mpeg-OTspec/files/20080814-w10068_14496-2
>> 
>	>2_FCD_2nd-Ed.zip> 
>	>
>	> 
>	>I will be on vacation Aug. 16-30 and will not have access to
>email. I
>	>would like to ask you to continue the review of the FCD text in
>	>preparation for our AHG meeting/teleconference on September 8.
>I will
>	>announce the detailed agenda for the call as soon as I come
>back from
>	>vacation.
>	> 
>	>Thank you,
>	>Vladimir
>	
>
>	 
>
>