PostScript fonts

PostScript fonts are outline font specifications developed by Adobe Systems for professional digital typesetting, which uses PostScript file format to encode font information.

History

Type 1 and Type 3 fonts, though introduced by Adobe in 1984 as part of the PostScript page description language, did not see widespread use until March 1985 when the first laser printer to use the PostScript language, the Apple LaserWriter, was introduced. Even then, in 1985, the outline fonts were resident only in the printer, and the screen used bitmap fonts as substitutes for outline fonts.

Although originally part of PostScript, Type 1 fonts used a simplified set of drawing operations compared to ordinary PostScript (programmatic elements such as loops and variables were removed, much like PDF), but Type 1 fonts added "hints" to help low-resolution rendering. Originally, Adobe kept the details of their hinting scheme undisclosed and used a (simple) encryption scheme to protect Type 1 outlines and hints, which still persists today (although the encryption scheme and key has since been published by Adobe). Despite these measures, Adobe's scheme was quickly reverse engineered by other players in the industry. Adobe nevertheless required anyone working with Type 1 fonts to license their technology.

Type 3 fonts allowed for all the sophistication of the PostScript language, but without the standardized approach to hinting (though some companies such as ATF implemented their own proprietary schemes) or an encryption scheme. Other differences further added to the confusion.

The cost of the licensing was considered very high at this time, and Adobe continued to stonewall on more attractive rates. It was this issue that led Apple to design their own system, TrueType, around 1991. Immediately following the announcement of TrueType, Adobe published ”Adobe type 1 font format”,[1] a detailed specification for the format. Font development tools such as Fontographer added the ability to create Type 1 fonts. The Type 2 format has since been used as one basis for the modern OpenType Format.

Technology

By using PostScript (PS) language, the glyphs are described with cubic Bézier curves (as opposed to the quadratic curves of TrueType), and thus a single set of glyphs can be resized through simple mathematical transformations, which can then be sent to a PostScript-ready printer. Because the data of Type 1 is a description of the outline of a glyph and not a raster image (i.e. a bitmap), Type 1 fonts are commonly referred to as "outline fonts," as opposed to bitmap fonts. For users wanting to preview these typefaces on an electronic display, small versions of a font need extra hints and anti-aliasing to look legible and attractive on screen. This often came in the form of an additional bitmap font of the same typeface, optimized for screen display. Otherwise, in order to preview the Type 1 fonts in typesetting applications, the Adobe Type Manager utility was required.

Font type

Type 0

Type 0 is a "composite" font format - as described in the PostScript Language Reference Manual, 2nd Edition. A composite font is composed of a high-level font that references multiple descendent fonts.

Type 1

PostScript Type 1
Filename extension

Windows & OS/2:
.pfb, .pfm, .afm
Mac OS:
.pfm, .afm,
.inf (Optional files).
Linux:
.pfa, .afm
OS/2:

.ofm
Type code

Mac: : LWFN  (prn/outline-data/Mac-bitmap).
sfnt (Mac PS1 bitmap) suitcase file.
printer (prn) outline (FOND/bitmap) file.
ffil (display).
FFIL (suitcase/screen).
Win: : binary (.pfb).
Developed by Adobe Systems
Type of format PostScript outline font
Extended to .otf (OpenType PostScript).
Standard ISO 9541

Type 1 (also known as PostScript, PostScript Type 1, PS1, T1 or Adobe Type 1) is the font format for single-byte digital fonts for use with Adobe Type Manager software and with PostScript printers. It can support font hinting.

It was originally a proprietary specification, but Adobe released the specification to third-party font manufacturers provided that all Type 1 fonts adhere to it.

Type 1 fonts are natively supported in Mac OS X, and in Windows 2000 and later via the GDI API.[2] (They are not supported in the Windows GDI+, WPF or DirectWrite APIs.)

Type 2

Type 2 is a character string format that offers a compact representation of the character description procedures in an outline font file. The format is designed to be used with the Compact Font Format (CFF). The CFF/Type2 format is the basis for Type 1 OpenType fonts, and is used for embedding fonts in Acrobat 3.0 PDF files (PDF format version 1.2).

Type 3

Type 3 font (also known as PostScript Type 3 or PS3, T3 or Adobe Type 3) consists of glyphs defined using the full PostScript language, rather than just a subset. Because of this, a Type 3 font can do some things that Type 1 fonts cannot do, such as specify shading, color, and fill patterns. However, it does not support hinting. Adobe Type Manager did not support Type 3 fonts, and they are not supported as native WYSIWYG fonts on any version of Mac OS or Windows.

Type 4

Type 4 is a format that was used to make fonts for printer font cartridges and for permanent storage on a printer's hard disk. The character descriptions are expressed in the Type 1 format. Adobe does not document this proprietary format.

Type 5

Type 5 is similar to the Type 4 format but is used for fonts stored in the ROMs of a PostScript printer. It is also known as CROM font (Compressed ROM font).

Types 9, 10, 11

Ghostscript referred them as CID font types 0, 1, and 2 respectively, documented in Adobe supplements. Types 9, 10, 11 are CIDkeyed fonts for storing Types 1, 3, 42 respectively.

Type 14

Type 14, or the Chameleon font format, is used to represent a large number of fonts in a small amount of storage space. The core set of Chameleon fonts consists of one Master Font, and a set of font descriptors that specify how the Master Font is to be adjusted to give the desired set of character shapes for a specific typeface.

Adobe does not document the Type 14 format.

Type 32

Type 32 is used for downloading bitmap fonts to PostScript interpreters with version number 2016 or greater. The bitmap characters are transferred directly into the interpreter's font cache, thus saving space in the printer's memory.

Type 42

The Type 42 font format is a PostScript wrapper around a TrueType font, allowing PostScript-capable printers containing a TrueType rasterizer (which was first implemented in PostScript interpreter version 2010 as an optional feature, later standard) to print TrueType fonts. Support for multibyte CJK TrueType fonts was added in PostScript version 2015. The out-of-sequence choice of the number 42 is said to be a jesting reference to The Hitchhiker's Guide to the Galaxy, where 42 is the Answer to Life, the Universe, and Everything.

Core Font Set

In addition to font types, PostScript specifications also defined the Core Font Set, which dictates the minimum number of fonts, and character sets to be supported by each font.

In original PostScript, there are 13 base fonts:

In PostScript Level 2, there are 35 fonts, which is a superset of the 13 base fonts:

In PostScript 3, 136 fonts are specified, which includes the standard 35 fonts; core fonts in Windows 95, Windows NT and Macintosh; selected fonts from Microsoft Office and the HP 110 font set. New fonts include:

In PDF, the following 14 fonts are defined:

However, in recent versions of Adobe Reader, Helvetica and Times were internally replaced by Arial and Times New Roman respectively.[3]

Character sets

Although PostScript fonts can contain any character set, there are character sets specifically developed by Adobe, which are used by fonts developed by Adobe.

Adobe Western 2

It includes a basic character set containing upper and lowercase letters, figures, accented characters, and punctuation. These fonts also contain currency symbols (cent, dollar, euro, florin, pound sterling, yen), standard ligatures (fi, fl), common fractions (1/4, 1/2, 3/4), common mathematics operators, superscript numerals (1,2,3), common delimiters and conjoiners, and other symbols (including daggers, trademark, registered trademark, copyright, paragraph, litre and estimated symbol). Compared to the ISO-Adobe character set, Western 2 also adds 17 additional symbol characters: euro, litre, estimated, omega, pi, partialdiff, delta, product, summation, radical, infinity, integral, approxequal, notequal, lessequal, greaterequal, and lozenge.

Fonts with an Adobe Western 2 character set support most western languages including Afrikaans, Basque, Breton, Catalan, Danish, Dutch, English, Finnish, French, Gaelic, German, Icelandic, Indonesian, Irish, Italian, Norwegian, Portuguese, Sami, Spanish, Swahili and Swedish.

This standard superseded ISO-Adobe as the new minimum character set standard as implemented in OpenType fonts from Adobe.

Adobe CE

Fonts with an Adobe CE character set also include the characters necessary to support the following central European languages: Croatian, Czech, Estonian, Hungarian, Latvian, Lithuanian, Polish, Romanian, Serbian (Latin), Slovak, Slovenian and Turkish.

Adobe-GB1

This Simplified Chinese character collection provides support for the GB 1988-89, GB 2312-80, GB/T 12345-90, GB 13000.1-93, and GB 18030-2005 character set standards. Supported encodings include ISO-2022, EUC-CN, GBK, UCS-2, UTF-8, UTF-16, UTF-32, and the mixed one, two- and four-byte encoding as published in GB 18030-2005.

Adobe-CNS1

This Traditional Chinese character collection provides support for the Big-5 and CNS 11643-1992 character set standards. It also includes support for a number of extensions to Big-5, which contain characters used mainly in the Hong Kong locale. Primary supported Big-5 extensions include HKSCS.

Supported encodings include ISO-2022, EUC-TW, Big Five, UCS-2, UTF-8, UTF-16, and UTF-32.

Adobe-Japan1

It is a series of character sets developed for Japanese fonts. Adobe's latest, the Adobe-Japan1-6 set covers character sets from JIS X 0208, ISO-2022-JP, Microsoft Windows 3.1 J, JIS X 0213:2004, JIS X 0212-1990, Kyodo News U-PRESS character set.

Adobe-Japan2

It was originally as an implementation of JIS X 0212-1990 character set standard and the Macintosh extensions, but with the introduction of Adobe-Japan1 supplement 6 (Adobe-Japan1-6) standard, Adobe-Japan2-0 became obsolete.

Adobe-Korea1

This Korean character collection provides support for the KS X 1001:1992 and KS X 1003:1992 character set standards, and their selected corporate variations. Supported encodings include ISO-2022-KR, EUC-KR, Johab, UHC, UCS-2, UTF-8, UTF-16, and UTF-32.

ISO-Adobe

Fonts with an ISO-Adobe character set support most western languages including: Afrikaans, Basque, Breton, Catalan, Danish, Dutch, English, Finnish, French, Gaelic, German, Icelandic, Indonesian, Irish, Italian, Norwegian, Portuguese, Sami, Spanish, Swahili and Swedish. This is the standard character set in most PostScript Type 1 fonts from Adobe.

File formats

CID

The CID-keyed font (also known as CID font, CID-based font, short for Character Identifier font) is a font structure, originally developed for PostScript font formats, designed to address a large number of glyphs. It was developed to support pictographic East Asian character sets, as these comprise many more characters than the Latin, Greek and Cyrillic writing systems.

Adobe developed CID-keyed font formats to solve problems with the OCF/Type 0 format, for addressing complex Asian-language (CJK) encoding and very large character sets. CID-keyed internals can be used with the Type 1 font format for standard CID-keyed fonts, or Type 2 for CID-keyed OpenType fonts. CID-keyed fonts often reference "character collections," static glyph sets defined for different language coverage purposes. Although in principle any font maker may define character collections, Adobe's are the only ones in wide usage. Each character collection has an encoding which maps Character IDs to glyphs. Each member glyph in a character collection is identified by a unique character identifier (CID). Such CIDs are generally supplemental to other encodings or mappings such as Unicode.

Character collections are uniquely named by registry, ordering and supplement, such as "Adobe-Japan1-6." The registry is the developer (such as Adobe). The so-called "ordering" gives the purpose of the collection (for example, "Japan1"). The supplement number (such as 6) indicates incremental additions: for a given language, there may be multiple character collections of increasing size, each a superset of the last, using a higher supplement number. The Adobe-Japan1-0 collection is 8284 glyphs, while Adobe-Japan1-6 is 23,058 glyphs.

CID-keyed fonts may be made without reference to a character collection by using an "identity" encoding, such as Identity-H (for horizontal writing) or Identity-V (for vertical). Such fonts may each have a unique character set, and in such cases the CID number of a glyph is not informative; generally the Unicode encoding is used instead, potentially with supplemental information.

CID-keyed fonts internally have their character sets divided into "rows," with the advantage that each row may have different global hinting parameters applied.

In theory it would be possible to make CID-keyed OpenType versions of western fonts. This would seem desirable for some such fonts because of the hinting advantages. However, according to Adobe, much of the software infrastructure (applications, drivers, operating systems) makes incorrect assumptions about CID-keyed fonts in ways that makes such fonts behave badly in real-world usage.

Adobe ClearScan technology (as from Acrobat 9) creates custom Type1-CID fonts to match the visual appearance of a scanned document after optical character recognition (OCR). ClearScan (in Acrobat 9) does not replace the fonts with your system fonts or substitute them by Type1-MM (as in Acrobat 8 and earlier versions), but uses these newly created custom fonts. The custom fonts are embedded in the PDF file (this is obviously mandatory).

Compact Font Format

Compact Font Format (also known as CFF font format, Type 2 font format, or CFF/Type 2 font format) is a lossless compaction of the Type 1 format using Type 2 charstrings. It is designed to use less storage space than Type 1 fonts, by using operators with multiple arguments, various predefined default values, more efficient allotment of encoding values and shared subroutines within a FontSet (family of fonts).

The so-called PostScript or Type 1 flavor of OpenType fonts, also called OpenType CFF, contains glyph outlines and hints in a CFF table.

CFF fonts can be embedded in PDF files, starting with PDF version 1.2. It is the usual approach to representing a Type 1 font within PDF.

CID-keyed fonts can be represented within CFF with Type 2 charstrings for CID-keyed OpenType fonts.

A Type 1 font can be losslessly converted into CFF/Type2 format and back.

Multiple Master

Main article: Multiple master fonts

Multiple master fonts (or MM fonts) are an extension to Adobe Systems' Type 1 PostScript fonts. Multiple master fonts contain one or more "masters" — that is, original font styles, e.g. a light, a regular and a bold version — and enable a user to interpolate these font styles along a continuous range of "axes." While Multiple Master font are not common in end user fonts anymore, they still play an important role when developing complex font families.

OpenType

Main article: OpenType

PostScript glyph data can be embedded in OpenType font files, but OpenType fonts are not limited to using PostScript outlines. PostScript outlines in OpenType fonts are encoded in the Type2 Compact Font Format (CFF).

OpenType conversion

When Adobe converted PostScript Type 1 and Type 1 multiple master fonts to OpenType CFF format, they were made based on the last Type 1/MM versions from the Adobe Type Library fonts. In addition to file format change, there are other changes:

For many Adobe Originals fonts, particularly those designed by Robert Slimbach, Adobe did some degree of redesign along with the conversion to OpenType.

The typeface Helvetica Narrow was not converted to OpenType, because the Type 1 original was a mathematically squished version of Helvetica, rather than an actually designed condensed typeface. This was originally done to conserve ROM space in PostScript printers.[4]

As a result of the above changes, Adobe no longer guarantees metric compatibility between Type 1 and OpenType fonts. However, Adobe claims the change is minimal for Adobe (not Adobe Originals) fonts, if:

Original Composite Font

Original Composite Font format (which uses a Type 0 file structure) was Adobe's first effort to implement a format for fonts with large character sets, debuted with PostScript level 2.

Adobe then developed the CID-keyed font file format which was designed to offer better performance and a more flexible architecture for addressing the complex Asian-language encoding and character set issues. Adobe does not document or support OCF font format.

OCF font metrics are described in Adobe Composite Font Metrics file.

Adobe Font Metrics, Adobe Composite Font Metrics, Adobe Multiple Font Metrics

Adobe Font Metrics (AFM), Adobe Composite Font Metrics (ACFM), Adobe Multiple Font Metrics (AMFM) files contain general font information and font metrics information for the font program. These files are generally used directly only in Unix environments.

An AFM file provides both global metrics for a font program and the metrics of each individual character.

The metrics of a multiple master font are described by one AMFM file, which specifies the control data and global font information, plus one AFM file for each of the master designs in the font.

An ACFM file provides information about the structure of a composite font. Specifically, the global metrics of the composite font program and the global metrics of each of its immediately descendent font programs. ACFM file does not associate with a base font, but act as the top-level structure of a composite font. The character metrics of individual characters in the composite font are described completely by one of more associated AFM files.

The formats are sufficiently similar that a compliant parser can parse AFM, ACFM, and AMFM files.

Printer Font ASCII

Printer Font ASCII (PFA) is an ASCII version of PFB, usually carrying ".PFA" file name extension. It contains a font's glyph data. PFA is the form of the font used by PostScript-language interpreters, and is also the preferred format for Type 1 fonts used in UNIX environments.

Printer Font Binary

Printer Font Binary (PFB) is a binary PostScript font format created by Adobe Systems, usually carrying ".PFB" file name extension. It contains a font's glyph data.

Printer Font Metric

Printer Font Metric (PFM) is a binary version of AFM, usually carrying ".PFM" file name extension. It contains font metric information.

The PFM format is documented in the Windows 3.1 "Printers and Fonts Kit" help file (PFK31WH.HLP). Some details are also covered in the Windows 3.1 "Device Drivers Adaptation Guide" help file (DDAG31WH.HLP). Both of those documents are part of the Windows 3.1 Device Development Kit (DDK), which is still available (October 2008) to MSDN subscribers.

.INF

.inf (INFormation) files contain application-specific information in plain ASCII text, such as font menu names for Windows and DOS-based applications. When a font is installed in Windows, the ATM Installer software takes the AFM and the INF file as input and generates the required PFM file at installation time. The AFM and INF files are not installed in the user's system.

.MMM

.MMM files are used for the metric data needed by multiple master fonts for the Windows environment.

.OFM

.OFM is the extension used by OS/2 for its version of binary font metrics file, starting from version 2.1.

Windows support

Windows 95, Windows 98, Windows NT and Windows Me do not support Type 1 fonts natively. Adobe Type Manager is needed in order to use these fonts on these operating systems. Windows 2000, Windows XP and Windows Vista support Type 1 fonts natively through GDI calls. The Windows Presentation Foundation introduced in Windows Vista, which is also available for Windows XP however drops support for Type 1 fonts, in favor of Type 2 fonts.

For Windows platforms that natively support PostScript, only binary PostScript and OpenType file formats are supported.

Windows Presentation Foundation (formerly codenamed Avalon) in Windows Vista supports rasterizing OpenType CFF/Type 2 fonts, whereas Type 1 fonts will still be supported in GDI, but not in GDI+.

PostScript font utilities

The t1utils font utility package by I. Lee Hetherington and Eddie Kohler provides tools for decoding Type 1 fonts into a human-readable, and editable format (t1disasm), reassembling them back into fonts (t1asm), for converting between the ASCII and binary formats (t1ascii and t1binary), and for converting from Macintosh PostScript format to Adobe PostScript font format (unpost).

See also

References

  1. ↑ "Adobe Type 1 Font Format" (PDF). Adobe Systems Inc. Retrieved 2015-05-22.
  2. ↑ Introduction to Configuration and Management: What's new in Windows 2000
  3. ↑ "Apache(tm) FOP: Fonts". xmlgraphics.apache.org. Retrieved 2014-06-08.
  4. ↑ Type 1 ("PostScript") to OpenType font conversion

External links

Wikibooks has a book on the topic of: PostScript FAQ

Type information

File format information

Character set information

Core font information

Miscellaneous

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