Auto Kerning Limitations?

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Metonymic
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Joined: Tue Mar 22, 2005 8:23 pm

Auto Kerning Limitations?

Post by Metonymic » Tue Mar 22, 2005 8:55 pm

Hello,
I'm new to font making, and to Font Creator. My question is this:

When using the automatic kerning wizard, is there a limit to the number of glyphs I can add? I have read the manual, and it says that one button will add all available glyphs, but I can't add more than 128 glyphs at one time. (I have some 250 glyphs in my font.) If I add the glyphs in smaller groups, the wizard only makes kerning pairs of the glyphs from the same group, and not of glyphs from the current group and the one added before. The solution to me seems to be adding pairs one at a time, which is why I want to use the wizard in the first place...

I'm probably missing something, but as I said before, I'm a newbie...

Apart from this issue, I'm very impressed by the program!!!

Thanks,
M.

Erwin Denissen
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Post by Erwin Denissen » Thu Mar 24, 2005 8:38 am

When you have 2 glyphs (for example A and W) selected in the Kerning wizard, it needs to calculate 2*2 = 4 possible kerning pairs:
AA
AW
WA
WW

When the user selects 256 glyphs, it has to go through 256 * 256 = 65536 possible kerning pairs. That would take a long time and then you most likely will run into the maximum kerning pairs limit of 10920.

Within the Automatic Kerning wizard do try to use a predefined kerning pair file (kern_standard.txt or kern_extended.txt) and see if that works for you.
Erwin Denissen
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FriFra
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Post by FriFra » Thu Mar 02, 2006 8:31 am

Erwin Denissen wrote:When use select 256 glyphs, it has to go through 256 * 256 = 65536 possible kerning pairs. That would take a long time and then you most likely will run into the maximum kerning pairs limit of 10920.
Is this a limitation of the fonts itself, or a limitation of the program?

Erwin Denissen
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Post by Erwin Denissen » Thu Mar 02, 2006 9:27 am

That is a limitation that affects all TrueType fonts due to the way kerning pairs are stored in fonts. It is a font specification restriction as explained here:
The length field in kerning subtables is saved as a 16-bit unsigned integer. This value includes the six byte header and the eight byte binary search information, so the maximum number of kerning pairs is (256 * 256 - 6 - 8) div 6 = 10920. More information about the kern table:
http://www.microsoft.com/typography/otspec/kern.htm

Usually this isn't a problem, because a well designed font (with bearings in the right place) needs only a few hundred kerning pairs.

OpenType fonts can use the OpenType kern feature that allows you to add more than 10920 kerning pairs, but that type of kerning won't work in a lot of software like Microsoft Word. More information about this:
http://www.microsoft.com/typography/ots ... res_ko.htm
http://www.microsoft.com/typography/otspec/gpos.htm

You might want to take a look at Microsoft VOLT as it can add OpenType features to your fonts.
http://communities.msn.com/MicrosoftVOLTuserscommunity
http://www.microsoft.com/typography/otf ... tures.aspx

Font Creator and VOLT can be used together as long as you don't change the order of the glyphs within Font Creator (so don't sort the glyphs). Also the postscript names should not be changed in Font Creator.
Erwin Denissen
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Erwin Denissen
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Post by Erwin Denissen » Thu Mar 02, 2006 2:21 pm

One more thing...

The best way to add kerning pairs is through 'Import kerningpairs from file'. Select 'kern_extended.txt' (more than 1000 kerning pairs) or 'kern_standard.txt' (more than 200 kerning pairs).

Hope this helps.
Erwin Denissen
High-Logic
Proven Font Technology

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