Re: OpenType vs TrueType (was current version of unicode-font)

From: John Hudson (
Date: Fri Dec 03 2004 - 12:47:32 CST

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    Gary P. Grosso wrote:

    > First, I see an "O" icon, not an "OT" icon in Windows' "Fonts folder" for some fonts and a "TT" icon for others. Nothing looks like "OT" to me, so are we talking about the same thing?

    > Next, if I double-click on one of the "fonts" (files), I get a window which shows a sample of the font, at the top of which is the font name, followed by either "(OpenType)" or "(TrueType)". Can I believe what that says as indicative of whether this is truly OpenType or TrueType?

    An OpenType font can contain either TrueType or Postscript (CFF) outlines and hints. A CFF
    flavour OT font, which will have the .otf extension, gets the O icon automatically, as
    determined by the presence of a 'CFF' table in the font. A TT flavour OT font may have
    either the .ttf or .otf extension (more likely the former, for backwards compatibility
    reasons), but will only get the O icon if the font contains a digital signature 'dsig'
    table. The reason for this is that the 'dsig' table is the only (optional) TT applicable
    table that was added to the OT spec that was not already part of the TT spec.

    The confusion for users is that the icon does not actually tell you anything very
    interesting or useful about the font, because what one really wants to know is whether the
    font contains OpenType Layout feature tables for glyph substitution and positioning. There
    was some talk at MS of changing the icon system in Longhorn, so that the O icon would
    reflect the presence of OTL tables in the font, but I don't know whether this will
    actually happen.

    > Mostly how this comes up is we have customers ask if we support OpenType fonts, to which I reply with some variation of "it depends". I usually say the OpenType spec is complex, but we handle all the commonly-used fonts we know of, and follow it by saying that they can look in their Fonts folder (at the icon) to see some examples of OpenType fonts. So that is the background for my questions.

    The issue of supporting OT fonts is complex because it can mean several different things.
    The OpenType file format is very widely supported (i.e. installable). Both outline and
    hint flavours are widely supported (i.e. rasterised). The OpenType Layout tables and
    features -- the stuff that most users think of when they hear 'OpenType', is supported to
    different levels in different system and application mixes, and is also likely to enjoy
    more support for some writing systems than others.

    John Hudson

    Tiro Typeworks
    Vancouver, BC
    Currently reading:
    The Peasant of the Garonne, by Jacques Maritain
    Art and faith, by Jacques Maritain & Jean Cocteau
    Difficulites, by Ronald Knox & Arnold Lunn

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