What is the TRUE difference between TrueType outlines and PostScript outlines?

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Fumiko Take's picture
Joined: 24 Dec 2013 - 10:43am
What is the TRUE difference between TrueType outlines and PostScript outlines?

I've done some Internet searches, but all I've got is some big words such as "quadratic B-splines" or "cubic Bezier splines". I've examined some fonts and I've been assuming that TrueType outlines are controlled by on and off-curved nodes (which are easier to adjust), and PostScript outlines by on-curved and handled nodes (which feel much more like "Bezier" to me). But I've just found out that most fonts I have with the OTF extension are recognized with "OpenType Layout, TrueType outlines" and with "(OpenType)" going after their family names (they've got PostScript outlines as I assumed). What I've learned from the Internet is that fonts with such info should be OpenType TT fonts, with the TTF extension, with "(TrueType)" after the fonts' family names; the OTF suffix should goes with "OpenType Layout, PostScript outlines" (OpenType PS). Am I wrong or something weird is going with m,y Windows' font classifying?

Reynir Heiðberg Stefánsson's picture
Joined: 19 Nov 2010 - 11:15am

The main difference between the outlines is the type of splines and the direction of drawing – I think they're drawn clockwise in TT and counterclockwise in PS.

As for Windows, it considers a TrueType font to be OpenType if it finds a table named "DSIG" in it, OpenType being a sort-of super-TrueType that can hold either type of outline along with a zoo of positioning and substitution data tables.

Thomas Phinney's picture
Joined: 3 Sep 2002 - 11:00am

You're mostly right.

You have one badly incorrect assumption: actually, PostScript outlines are *much* easier to edit than TrueType outlines.

Donald H. Tucker's picture
Joined: 13 Dec 2012 - 3:47pm

I agree with Thomas. My first attempts to edit fonts -- with font editors that are long since obsolete -- were with true type and were extremely frustrating. Ps is a dream by comparison. But ps is weak for presentation of very complex designs, so ttf has its advantages. Otf is really just a wrapper for either ps or ttf formats. Either flavor can work fine as otf. Bit of history -- ps was the first really good digital font format, i.e. Adobe etc. Microsoft didn't own it, so promoted the alternative ttf. Even today, fonts packaged with Microsoft products are ttf.

Hrant H Papazian's picture
Joined: 3 May 2000 - 11:00am

FWIW IIRC David Berlow disagrees that TT is harder (although I might have misunderstood).