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

aki3k's picture

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?

Té Rowan's picture

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

You're mostly right.

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

donshottype's picture

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's picture

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


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