OpenType PS with 2048 UPM

Göran SöderströmGöran Söderström Posts: 117
edited May 2012 in Technique and Theory
I’m doing a very thin script and I really need a bigger UPM, what could be a real problem with a 2048 UPM on OpenType PS? I mean what could happen?


  • Why not convert the curves to TrueType and forget the worry?
  • Mark SimonsonMark Simonson Posts: 735
    edited May 2012
    The only problem I know of is a cosmetic one in certain (older?) Adobe apps. I seem to recall it was just in Illustrator. The inverted selection area that you get when you select text will be displayed at the wrong height. If it's a PS or CFF font, it assumes 1000 units and displays the selection area at that height even when the UPM is different. So, if your UPM is 2048, the selection area will be about half the expected height. The font will still work fine otherwise.
  • You don't need to round to full units in an OT/CFF. In Glyphs, set the grid to 0 and be as precise as you want.
  • Georg SeifertGeorg Seifert Posts: 418
    We had some problems with CFF fonts with an UPM bigger than ~5000. It looks fine on screen and print but you can’t convert it to outlines in Indesign and Illustrator (CS3+4). It will distort all paths above 5000 units. So if you go 4000 you are save, you do not need to use the TTF numbers.

    Or, as @mekkablue said, use fractional positioning in Glyphs. Disable the auto hinting as the adobe autohinter will do rounding. I have to rewire most of the adobe code to improve that.
  • To update my comment about the autohinter. I fixed the rounding problem and so now you can use fractional coordinates and use the autohinter.
  • We have some CFF font families with a 2048 UPM in the Adobe type library. I don’t believe it’s an issue.
  • Fonts with PS outlines (Type 1 and OpenType CFF) have a maximum coordinate value of +/- 4096. This is the biggest, albeit indirect, limitation on unusually large em squares for OpenType CFF (OTF) fonts.
  • That limitation can be a real problem in the horizontal direction, even at 1000 upm. I've run into it on several occasions.
  • RalfRalf Posts: 170
    Fonts with PS outlines (Type 1 and OpenType CFF) have a maximum coordinate value of +/- 4096.
    What does it mean? What will happen when larger values are used?
  • What does it mean? What will happen when larger values are used?
    I ran into trouble with glyphs wider than 5,000 units being invisible in MS Word. Everything else I tried handled them without error.
  • If you go beyond the 4096-unit limit, you are taking your chances. Lots of things will doubtless be fine, but without inspecting source code or experimenting, I don't know how one would predict what will fail.

    Anything that has its own unique native rendering capability for fonts would need to be tested. A few obvious ones:

    - OS X Quartz
    - Windows GDI
    - Windows DirectWrite
    - OpenType Sanitizer (in Firefox and Chrome)
    - FreeType
    - Adobe CoolType
    - Adobe PostScript (assorted version)
    - each different PostScript clone on the market
    - other printer drivers that have their own font rendering engine
    - etcetera

    Just for a start, I will bet (lunch at the next type conference we're both at) that the OpenType Sanitizer will reject an OTF with > 4096 upm. If it doesn't reject such a font today, and we tell them about it, they will make sure it does in the future. They are pretty eager to restrict fonts to confirm to published specs... even if Mac OS and Windows are fine with the fonts in question.


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