Type 1 font and Private dictionaries

A Type 1 font program builds a PostScript dictionary and registers it as a font. The clear text part (the first segment) fills in the keys anyone may read; the encrypted part adds the Private dictionary, which holds the hints and helper routines, and the CharStrings dictionary of glyph programs. Because the program is real PostScript, a reader that does not run PostScript has to recognise these keys and their usual syntax.

First line

A conforming font starts with %!FontType1-SpecVersion: FontName FontVersion, for example %!FontType1-1.0: Symbol 001.003; fonts from Adobe itself use %!PS-AdobeFont-1.0: FontName version, and software should accept both (Type 1 specification, section 2.3). DSC comments such as %%CreationDate and %%VMusage, the memory the font needs once loaded, may follow.

Font dictionary

Key	Type	Meaning
`FontType`	integer	1.
`FontName`	name	The PostScript name, e.g. `/Times-Roman`.
`FontInfo`	dictionary	Optional descriptive values, below.
`PaintType`	integer	0 the outlines are filled; 2 they are stroked.
`StrokeWidth`	number	Line width for `PaintType` 2, in glyph units.
`FontMatrix`	array of 6	Maps glyph units to the 1-unit text space; normally `[0.001 0 0 0.001 0 0]`, a 1000-unit em.
`Encoding`	array or name	`StandardEncoding`, or a 256-entry array of glyph names indexed by character code (unused codes `/.notdef`).
`FontBBox`	array of 4	Lower-left x, y and upper-right x, y of all glyphs, in glyph units.
`UniqueID`	integer	Optional number registered with Adobe so that printers can cache glyphs across jobs; 0 to 16,777,215 (2²⁴ − 1), separate for each FontType (section 2.5).
`XUID`	array	Optional extended unique ID: an organisation number followed by its own numbers (defined in the PostScript Language Reference Manual, not the Type 1 book).
`Private`	dictionary	Added by the encrypted part; below.
`CharStrings`	dictionary	Added by the encrypted part: glyph name → charstring. Must contain `/.notdef`.
`Metrics`, `Metrics2`, `CDevProc`	dictionaries, procedure	Optional overrides of glyph widths and side bearings, added by applications rather than font makers (`Metrics` appears in the Type 1 book’s figure 2b; the others are PostScript Level 2 additions).
`FSType`	integer	A later addition in some fonts: the embedding permissions, as in the OS/2 table’s `fsType`.

FontInfo

Key	Type	Meaning
`version`	string	Font version, e.g. `(001.007)`.
`Notice`	string	Trademark and copyright notice.
`FullName`	string	Full name for menus, e.g. `(Times Roman)`.
`FamilyName`	string	Family, e.g. `(Times)`.
`Weight`	string	Weight name, e.g. `(Roman)`, `(Bold)`.
`ItalicAngle`	number	Degrees anticlockwise from vertical; negative for fonts that lean right.
`isFixedPitch`	boolean	True if every glyph has the same width.
`UnderlinePosition`	number	Distance from the baseline to the underline, in glyph units (usually negative).
`UnderlineThickness`	number	Underline thickness, in glyph units.

Fonts may add other entries (Adobe’s 1990 fonts include a Copyright string).

Private dictionary

The encrypted part starts by creating the Private dictionary. Its hint values let the rasteriser keep stems even and line up the tops and bottoms of letters at small sizes. All values are in glyph units unless stated.

Key	Type	Meaning
`RD` or `-\|`	procedure	Reads the binary charstring that follows: `{string currentfile exch readstring pop}`.
`ND` or `\|-`	procedure	Defines a glyph: `{noaccess def}`.
`NP` or `\|`	procedure	Stores a subroutine: `{noaccess put}`.
`BlueValues`	array, up to 14	Required. Pairs of y values giving alignment zones: the first pair is the baseline overshoot zone, the rest zones above it (x-height, cap height, ascender…). In ascending order.
`OtherBlues`	array, up to 10	Pairs of zones below the baseline (descenders).
`FamilyBlues`	array, up to 14	The family’s regular-weight `BlueValues`, used at small sizes so the family aligns.
`FamilyOtherBlues`	array, up to 10	The family’s `OtherBlues`.
`BlueScale`	number	The point size (as a ratio) below which overshoots are suppressed; default 0.039625, which is 10 points at 300 dpi (section 5.6).
`BlueShift`	integer	Overshoots at least this deep are kept above the `BlueScale` size; default 7.
`BlueFuzz`	integer	How far outside a zone an edge may be and still be aligned to it; default 1.
`StdHW`	array of 1	The dominant horizontal stem width.
`StdVW`	array of 1	The dominant vertical stem width.
`StemSnapH`	array, up to 12	Common horizontal stem widths, including `StdHW`, in ascending order.
`StemSnapV`	array, up to 12	Common vertical stem widths.
`ForceBold`	boolean	Thicken thin stems at small sizes (for bold fonts).
`LanguageGroup`	integer	0 Latin, Greek, Cyrillic and similar; 1 Chinese, Japanese and Korean ideographs, which use different stem rules.
`ExpansionFactor`	number	For `LanguageGroup` 1: how much a counter may grow to keep stems apart; default 0.06.
`lenIV`	integer	Number of random bytes at the start of each charstring; default 4. The original LaserWriter’s interpreter (version 23.0) needs 4; otherwise 0 or 1 saves space (section 5.12).
`password`	integer	Compatibility entry, required: always 5839 (section 5.13).
`MinFeature`	array of 2	Obsolete compatibility entry, required: always `{16 16}` (section 5.13).
`UniqueID`	integer	The same value as in the font dictionary.
`RndStemUp`	boolean	Superseded by `LanguageGroup`. A language group 1 font must also include `/RndStemUp false def` for older interpreters; no other font should mention it (section 5.11).
`Subrs`	array	Charstring subroutines, called with `callsubr`; see below.
`OtherSubrs`	array of procedures	PostScript procedures called from charstrings with `callothersubr`, for flex and hint replacement.

Subrs, OtherSubrs and CharStrings syntax

/Subrs count array
dup 0 n RD n encrypted bytes NP
dup 1 n RD n bytes NP
…
ND
2 index /CharStrings count dict dup begin
/.notdef n RD n bytes ND
/space n RD n bytes ND
…
end
end
readonly put
noaccess put
dup /FontName get exch definefont pop
mark currentfile closefile

Each entry is a count of bytes, the RD procedure, one space and then exactly that many bytes of encrypted charstring. If a font uses flex or hint replacement, its first four Subrs must be these fixed helpers (section 8.4); otherwise Subrs 0 may be an ordinary subroutine:

Subrs	Contents	Use
0	`3 0 callothersubr pop pop setcurrentpoint return`	Ends a flex sequence.
1	`0 1 callothersubr return`	Starts a flex sequence.
2	`0 2 callothersubr return`	Adds a point to a flex sequence.
3	`return`	Does nothing; called during hint replacement by interpreters without `OtherSubrs` 3 (see hint replacement).

OtherSubrs	Purpose
0	End of flex: draw the two curves as a flat line or as curves depending on the size.
1	Start of flex.
2	Collects one flex point.
3	Hint replacement.
4 and up	Reserved by the Type 1 specification for future extensions (chapter 8). Later Adobe documents use further entries for counter control and Multiple Master fonts; those are not covered here.

The OtherSubrs procedures themselves are a fixed block of PostScript published by Adobe, which fonts copy unchanged; interpreters such as FreeType implement their effect directly rather than running them.

Example

The clear text font dictionary of Times Roman (TIR_____.PFB, 1990), with the long copyright strings shortened:

%!PS-AdobeFont-1.0: Times-Roman 001.007
%%CreationDate: Tue Mar 20 12:15:38 1990
%%VMusage: 30487 37379
11 dict begin
/FontInfo 10 dict dup begin
/version (001.007) readonly def
/Notice (Copyright (c) 1985, 1987, 1989, 1990 Adobe Systems Incorporated. …) readonly def
/Copyright ( … ) readonly def
/FullName (Times Roman) readonly def
/FamilyName (Times) readonly def
/Weight (Roman) readonly def
/ItalicAngle 0 def
/isFixedPitch false def
/UnderlinePosition -100 def
/UnderlineThickness 50 def
end readonly def
/FontName /Times-Roman def
/Encoding StandardEncoding def
/PaintType 0 def
/FontType 1 def
/FontMatrix [0.001 0 0 0.001 0 0] readonly def
/UniqueID 28416 def
/FontBBox{-168 -218 1000 898}readonly def
currentdict end
currentfile eexec

A 1000-unit em, filled outlines, the standard Latin encoding, and glyphs reaching from 218 units below the baseline to 898 above. Everything after eexec is in the encrypted segment.

.PFB File Format – Font and Private dictionaries