Help with LTSH and VDMX tables.

Sorry to bother, but I was wondering if anyone could help. I'm relatively new to type design, I've only been at for like 8 months and self taught, there's much I don't know. I thought I had finally finished my first font, but some issues were found (please look below). I have no idea what that is or how to fix it. I also couldn't find anything about LTSH and VDMX tables in Fontlab, I might not have looked hard enough though. Any help would be appreciated.

• in the LTSH table many (almost all) values are incorrect, some seem to be really massively off (https://docs.microsoft.com/en-us/typography/opentype/spec/ltsh)
• in the VDMX table many (seemingly all) values are larger by one unit than needed (https://docs.microsoft.com/en-us/typography/opentype/spec/vdmx). This may be responsible for the error report regarding vertical metrics.
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Comments

  • Mike DugganMike Duggan Posts: 187
    how did you make this font? is it a TrueType font generated from FontLab? its possible you don't need these tables at all. how were the issues with the tables found?
  • John HudsonJohn Hudson Posts: 1,657
    Which version of FontLab?
  • Which version of FontLab?
    Fontlab Studio 5
  • how did you make this font? is it a TrueType font generated from FontLab? its possible you don't need these tables at all. how were the issues with the tables found?
    The font was generated in Fontlab Studio 5 as a TrueType font. The issues with the tables was found when I tried to submit the font to MyFonts. Their validator kept detecting vertical clipping even though all the Ascenders/Descenders (OS/2, hhea) seemed to be good. I contacted their support and they too were able to replicate the issue. They passed it along to a developer. The developer said that the LTSH and VDMX tables "may be responsible for the error report regarding vertical metrics."
  • how is the font hinted? 
  • Thomas PhinneyThomas Phinney Posts: 1,633
    I would wonder what happens if you just open the source in FontLab VI and regenerate it from there. Does that resolve the problem? You can use VI in free trial mode for a month.

    (Not that I am directly affiliated with FontLab these days.)
  • John HudsonJohn Hudson Posts: 1,657
    Microsoft had a command line tool called cachett that correctly calculates the device metrics values, and this could be set to run automatically when exporting fonts from the Windows version of FontLab Studio 5. Unfortunately, this tool doesn't seem to be available from the new version of the MS Typography website.
  • Mike DugganMike Duggan Posts: 187
    hi Giancarlo, as you say you are new to font design, I am going to assume you are not too concerned with the hinting in your font, (hinting is a set of instructions in the font, to help letterforms better fit the screen pixel grid). The tables you refer to are Hinting related, and you probably do not need them.

    a couple of things however. its possible you might want the tables? I have ben trying to find out how/why these tables were generated in the first place. this is best answered by Font Lab folks, but I have not been able to get the right person. I think its important to know why the tables are there. it could be as Thomas suggested that newer versions of FL do not make these tables in the font, and they are no longer required for general use fonts.

    if we do figure out that the tables are not needed, the next step is to remove them. I can probably work with you to help you do that. 

    you could try Thomas's suggestion first, to see if that resolves the issue. in the meantime I can try get someone from FontLab to comment here. cant promise anything on that. 
  • I would wonder what happens if you just open the source in FontLab VI and regenerate it from there. Does that resolve the problem? You can use VI in free trial mode for a month.

    (Not that I am directly affiliated with FontLab these days.)
    Thanks for the tip, but apparently I've already used the free trial. Can't remember when that was. So, sadly I couldn't try your suggestion. I appreciate it nonetheless.
  • edited August 12
    hi Giancarlo, as you say you are new to font design, I am going to assume you are not too concerned with the hinting in your font, (hinting is a set of instructions in the font, to help letterforms better fit the screen pixel grid). The tables you refer to are Hinting related, and you probably do not need them.

    a couple of things however. its possible you might want the tables? I have ben trying to find out how/why these tables were generated in the first place. this is best answered by Font Lab folks, but I have not been able to get the right person. I think its important to know why the tables are there. it could be as Thomas suggested that newer versions of FL do not make these tables in the font, and they are no longer required for general use fonts.

    if we do figure out that the tables are not needed, the next step is to remove them. I can probably work with you to help you do that. 

    you could try Thomas's suggestion first, to see if that resolves the issue. in the meantime I can try get someone from FontLab to comment here. cant promise anything on that. 
    I'm not sure if the hinting is needed. Its a display font intended to be used in Photoshop, Illustrator and the like. I'd prefer to get rid of the tables if they're not needed. If they are and if you can, link me anything you think I need to know for me to get the tables working properly. And thanks for the help.
  • Mike DugganMike Duggan Posts: 187
    if you can send me your final .ttf font, i can look into deleting the tables. you can send it to mikedu (at) microsoft.com 
  • This is the original cachett.exe file from microsoft (2002).
    Create a folder to download the file:
    In fontlab 5 go to Preference >Generating Truetype/OpentypeTT >Use cachett program to generate device metrics tables in TTF fonts link the file in the folder You choose.
    Try to generate your font again.
    Regards
    Sami

  • This is the original cachett.exe file from microsoft (2002).
    Create a folder to download the file:
    In fontlab 5 go to Preference >Generating Truetype/OpentypeTT >Use cachett program to generate device metrics tables in TTF fonts link the file in the folder You choose.
    Try to generate your font again.
    Regards
    Sami

    Ok, thanks for the file and the instructions. I saw it open a window when I went to generate the TTF, so I'm assuming it worked. Is there a way to know for sure, like a test?
  • Mike DugganMike Duggan Posts: 187
    there is some crazy hints in the font. let me send you a font, with the hinting gone, the tables deleted and the GASP set correctly. thanks mike
  • Ok, thanks for the file and the instructions. I saw it open a window when I went to generate the TTF, so I'm assuming it worked. Is there a way to know for sure, like a test?
    Did You try to generate a font using the microsoft cachett.exe.
    Probably the only way to know if it works.
    I am sure it will works.
    Sami
  • Mike DugganMike Duggan Posts: 187
    I sent on the font. some of the hinting in the font was causing some glyphs to appear much larger than they should have. I removed hinting, set the GASP table to use ysmoothing at all sizes. removed the LTSH and VDMX. 
  • Thomas PhinneyThomas Phinney Posts: 1,633
    Aha. So the crazy hinting was causing crazy effects at specific sizes, which then carried on to the LTSH and VDMX as they are based on size-specific rendering. I understand now.
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