Kerning Issue

Andrea T.

Hello everybody,

I'm wonder how many kerning pairs i can manage without having exportation problem. I mean, now in the metric window (kerning selected) show me #206 kerning pairs (this means that in the TTF file exported with fontlab i have #10920 pairs) this is a right number?

Thank you very much for your help

Erwin Denissen

It looks like you refer to the (almost) obsolete kern table instead of GPOS pair adjustment. Better avoid it unless you are editing an old font.

Andrea T.

So after editing kerning pair on fontlab kerning windows what i have to do to make otf and ttf exportation efficient ?

as you can see in the image below i have 217 kerning pairs grouped in classes. when i made ttf and otf exportation with trans type (from a ttf fontlab file) the result is files without kerning or at least without some kerning. Now i'm supposing that the kerning data is too much to be exported in ttf or otf files.
I'm trying to understand the problem but i didn't find a thread that teach a right process to produce files without loosing kerning data

Mike Wenzloff

The number of kerning pairs in a TTF is limited to 10,920 and if you have classes with pairs that exceed that number, then FL will truncate (If I recall properly) to that number. But your classes/pairs could exceed that number and will be fully exported to OTF direct from FL.

I'm on a mobile device and the screen shot is difficult to read, but if you really have a "flat" 219 pairs, then they all will be exported from FL to a TTF.

Andrea T.

@Mike Wenzloff
If "flat" means the total number of kerning pairs Including the permutation with each member of a class, this is not the case.
#217 is the number of kerning pairs "grouped" (i don't know how to call the non-flat pairs). You're right, in fact in the TTF the total number of pairs is exactly 10920...
If i understand the way it works, i will have no problem with OTF if i expand the kerning data...
So what i have to do in order to have a TTF file with every kerning pairs i set? is it possible or i just have to reduce them?

PS.: 
I'm trying to understand how kerning data works:
Which is the difference between the kerning data expanded in the open features panel, and the ones stored in the metric panel (kerning selected)?

...and which is the difference between "export old style non open type kern table" and "generate opentype kern features if it...." in term of exportation?




i'm really sorry if i bother you with all this stupid questions. But this problem is driving me mad
I really appreciate your help. Thank you so much.

Paul van der Laan

@Andrea T.: For OTF (and present day TTF) fonts you will only need to concern yourself with class kerning. There is a maximum amount of class kerning that a generated font can contain, but you should only start worrying about that the moment you exceed approx. 10,000 *class* kerning pairs. You don’t need to expand those classes.

The class kerning that your are seeing in the FontLab metrics window 
(those 219 pairs) needs to be converted to a "kern" feature when the font gets generated. That is what the "Generate OpenType "kern" feature... " preference is for. Just leave it on.

The preference to "Export old-style non-OpenType "kern" table" only applies to a very old standard for TrueType fonts. Don't bother with it unless you need to cater for very old versions of Windows.

I don’t see any need to use TransType to generate OTF and TTF files. Why not generate them completely from FontLab?

A lot of this is also explained in the FontLab pdf manual, which you can find in the "Help" menu.

Hope this helps!

Andrea T.

@Paul van der Laan
Thank you very much Paul for your answer!
I think i execeeded the maximum number of pairs. 

This is the TTF exportation  with #10920 pairs
(on the right of the window there are the class kerning pairs expanded? In the first image, the one i posted yesterday, i can see on the right the class kerning pairs "grouped"?)


Thank you again!

Paul van der Laan

Your welcome @Andrea T..

Really, you don’t need to expand the class kerning *at all*. And if this is happening automatically then you need to check where this happens.

Stick to "grouped" class kerning and let FontLab generate the "kern" feature.

Generate the fonts from FontLab directly, and make sure the preferences are set according to my previous post. That should do the trick.

Andrea T.

Thank you very much @Paul van der Laan everything works fine now!