OTF & TTF font files

[Michael Rowley]

I came across this statement a liitle while ago:

'Fonts containing TrueType outlines may have either .OTF or .TTF, depending on the desire for backward compatibility on older systems or with previous versions of the font.'

Has anyone ever come across an OTF file containing TrueType outlines, and if so, who was the maker?

[iamback]

Originally Posted by Michael Rowley

Has anyone ever come across an OTF file containing TrueType outlines, and if so, who was the maker?

How would I tell if a file (with an .otf extension) has TrueType outlines? I can't answer the question if I don't know what to look for.

[ktinkel]

Originally Posted by Michael Rowley

Has anyone ever come across an OTF file containing TrueType outlines, and if so, who was the maker?

As far as I understand it, the OTF designation refers to an OpenType font that contains Type 1 outlines. OT fonts containing TrueType outlines (should) have a TTF suffix.

The $20 Ascender font pack contains all OT/TTF fonts.

[ktinkel]

Originally Posted by iamback

How would I tell if a file (with an .otf extension) has TrueType outlines?

By definition, .OTF fonts contain PostScript Type 1 outlines. The OT fonts with .TTF have TrueType outlines.

[Michael Rowley]

Originally Posted by iamback

How would I tell if a file (with an .otf extension) has TrueType outlines? I can't answer the question if I don't know what to look for.

You (possibly) and I (certainly) wouldn't know if a font file with the extension OTF had TrueType or PS outlines, partly because both of us use Windows NT5, which doesn't care; probably many are in the same position, but there are some experts on fonts here. If you're not an expert, you'll rely on the maker's information, which is how I 'know' that all Adobe font files with OTF extensions have PS outlines.

[Michael Rowley]

Originally Posted by ktinkel

By definition, .OTF fonts contain PostScript Type 1 outlines. The OT fonts with .TTF have TrueType outlines.

Not according to the Microsoft document from which I just quoted. All Adobe OTF files have PS outlines (and all files supplied by Microsoft have TTF extensions and outlines), but that doesn't necessarily apply to every maker.

[iamback]

Originally Posted by Michael Rowley

You (possibly) and I (certainly) wouldn't know if a font file with the extension OTF had TrueType or PS outlines, partly because both of us use Windows NT5, which doesn't care

But a hex viewer doesn't care about NT5. I was thinking there must be some sort of signature that enables one (or software) to tell them apart since an extension is essentially meaningless anyway.

[Michael Rowley]

Originally Posted by iamback

But a hex viewer doesn't care about NT5. I was thinking there must be some sort of signature that enables one (or software) to tell them apart since an extension is essentially meaningless anyway.

Yes, of course there is, but you will have to go to the Open Type Specification for that.

Since the specification is the joint work of Adobe and Microsoft, the statement by M. that an OTF file may contain TrueType outlines could be true, but never implemented by anybody; or it could have been M.'s intention to use the OTF extension for its OT files, but thought better of it.

[iamback]

Originally Posted by ktinkel

As far as I understand it, the OTF designation refers to an OpenType font that contains Type 1 outlines. OT fonts containing TrueType outlines (should) have a TTF suffix.

Since Michael referred me to the Open Type Specification I went to look for that. The Microsoft site has the full specification online (and as a self-extracting archive (for which you'll need Windows of course)), and it seems like his quote comes straight from the spec. Here's a fuller quote (bold for headings, my emphasis):

The OpenType Font File

An OpenType font file contains data, in table format, that comprises either a TrueType or a PostScript outline font. (...)

Filenames

OpenType fonts may have the extension .OTF or .TTF, depending on the kind of outlines in the font and the creator's desire for compatibility on systems without native OpenType support.

• In all cases, fonts with only CFF data (no TrueType outlines) always have an .OTF extension.
• Fonts containing TrueType outlines may have either .OTF or .TTF, depending on the desire for backward compatibility on older systems or with previous versions of the font. TrueType Collection fonts should have a .TTC extension whether or not the fonts have OpenType layout tables present.

That seems clear enough to me.

[EDIT:] Of course Adobe has the specification online as well - same content (including the quote above!) although the table of contents is organized slightly differently.

[iamback]

Originally Posted by Michael Rowley

Yes, of course there is, but you will have to go to the Open Type Specification for that.

Found it (links in my reply to KT). The Organization of an OpenType Font section says:

OpenType fonts that contain TrueType outlines should use the value of 1.0 for the sfnt version. OpenType fonts containing CFF data should use the tag 'OTTO' as the sfnt version number.

NOTE: The Apple specification for TrueType fonts allows for 'true' and 'typ1' for sfnt version. These version tags should not be used for fonts which contain OpenType tables.

So... if I go looking first for files with an .OTF extension, and within that set for files which contain the string 'OTTO' then whatever is is not matched by the sub-search must be files with TrueType outlines (given I do not have Mac fonts - at least no working ones!). No hex viewer needed even, just plain Search can do that.

Result on my machine: 17 files with an ".otf" extension (lower case), 13 of which originating from Adobe; all 17 contain the string "OTTO".

Looking with a hex viewer at one of them, the string "OTTO" is right at the start of the file, so finding that (or another sfnt version) is simply a matter of looking at the first 4 bytes (provided the file contains only one font - but if it has multiple fonts it should have a TTC extension, not OTF).