PostScript font formats

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The PostScript font formats are a family of PostScript -based data formats for fonts , developed by Adobe Inc. The most important family member is type 1 (see below), which has also found widespread use outside of PostScript applications.

Glyphs are described in PostScript fonts using PostScript operations. As a rule, this is how the outlines of the characters (outline fonts) are saved. Depending on the subtype, the characters can also be saved as raster fonts (bitmap fonts) or any graphics that can be written using PostScript. In addition to the glyphs, PostScript fonts also define global properties such as name and typographical size.

history

In 1984 Adobe Systems and its Adobe Type PostScript division published the definition of font formats in 1985/86, thus revolutionizing previous typesetting ( photo typesetting ) and giving desktop publishing the breakthrough.

The specification of the Type 3 character sets was disclosed, but the license for the more mature Type 1 was sold at very high prices for the time. Adobe's patent policy led to the development of the TrueType format by Apple around 1991 , which was later used by Microsoft under license. In response, Adobe published the Adobe Type Manager (ATM), which improved the display of Type 1 PostScript fonts on the screen and with non-PostScript-compatible printers and the specifications of the format, including the successful reverse engineering by the font manufacturer Bitstream contributed. As a result, support for the Type 1 format was built into some font editors; some free fonts such as B. most of the fonts used by the TeX typesetting system in this format.

Multiple master fonts are a modification of the PostScript character set format. The so-called "Smartfont" technology in the implementation of OpenType is, so to speak, a further development of the Type 1 format.

Formats

Type 0
is a format for composite fonts that do not contain glyphs themselves, but reference other fonts. The type 0 format provides methods for converting a large number of characters such as B. to be addressed directly for Asian character sets.
The characters of a font are addressed in PostScript using a character list (encoding array) with 256 entries so that each byte of a character string corresponds to a glyph. If more characters of a font are required, you must explicitly switch between several instances of the same font with different encoding arrays within a document. Each instance is a separate font for the PostScript interpreter. A character string can only address characters from one of these instances.
Type 0 provides various coding methods that allow glyphs from different fonts to be addressed within a character string, so that effectively more than 256 characters are available. CID fonts (types 9, 10, 11 and 32), which are presented to the PostScript interpreter as a special form of type 0 fonts, avoid splitting a font into instances with a maximum of 256 characters.
Type 1
For type 1, an ISO -standardized (ISO 9541), restricted excerpt from the entire PostScript language range, which is available in a special coding, is used to describe the glyphs . The outlines of the characters are represented with the help of lines and Bézier curves of the third degree.
With the limitation of the PostScript language range for type 1 fonts, this type is a subset of type 3, in which, on the other hand, the full language range can be used. Because of this limitation, a full PostScript interpreter does not have to be available, which improves cross-platform processability. Similar to PDF , the format is no longer a complete programming language, but is limited to the means of describing the outlines of the glyphs.
Hints can also be used in a standardized manner within Type 1 fonts , which significantly improve the glyph display on devices with low resolution.
Type 1 has become more widespread than type 3.
Type 1 fonts are usually delivered in packages with at least two, but usually four files each:
.pfm (PostScript Font Metric)
Contains the thickness values ​​of the individual characters and kerning values ​​for character pairs (only required for Windows )
.pfb (PostScript Font Binary)
contains information about the font itself; an equivalent variant of this format uses the extension .pfa (PostScript Font ASCII) and contains only ASCII characters instead of any bytes
.inf (optional)
ASCII text file with general information on the coding and the dimensions of the characters (only required for Windows)
.afm( Adobe Font Metrics , optional)
the Adobe Font Metrics file, with an information content identical to the PFM file in an easily processable (editable) ASCII text format
Type 2
is a string format (as opposed to a file format) for storing the descriptions of glyphs. It is used with the Compact Font Format (CFF) and in this combination is the basis of Type 1 OpenType fonts. It is used in version 1.2 of PDF (Acrobat 3.0) to embed fonts in PDF files.
Type 3
is a font format that is the forerunner of Type 1. With type 3 the glyphs are described in unrestricted PostScript, which means that additional properties such as colors, shading and fill patterns can be defined compared to type 1, but hinting is not supported.
Type 3 fonts are not supported by Adobe Type Manager.
Type 4
is a format that was used to describe fonts that were permanently stored on built-in storage devices in printers (font cartridges, hard drives). The character descriptions follow the type 1
format. There is no manufacturer documentation on this proprietary format.
Type 5
(also known as Compressed ROM font, CROM font) is similar to Type 4, but specifically for fonts that are stored in the read-only memories of PostScript printers.
Types 9, 10, 11
are CID-coded fonts (Character Identifier fonts) that are processed with the help of type 0 technology. The description of the glyphs for types 9, 10 and 11 is in the same form as for types 1, 3 and 42. You identify yourself using the CID font type 0, 1 and 2, which can be distinguished from the font type (9, 10 or 11).
Type 14
Type 14, also known as the Chameleon font format, is used to display a large number of fonts with low memory requirements. At its core, Chameleon fonts consist of a main font and a set of descriptions to customize their glyphs to achieve a character set of a particular appearance.
There is no documentation from the manufacturer for Type 14.
Type 32
is used to download raster fonts to PostScript interpreter version 2016 or higher. The raster graphic glyphs are loaded directly into the interpreter's font memory, which saves printer memory. Type 32 identifies itself as CID font type 4.
Type 42
The Type 42 format is a PostScript adapter for TrueType fonts, the PostScript capable printers with TrueType raster unit (which was introduced in version 2012 of the PostScript interpreter initially as an optional feature and later as standard) the printing of TrueType Fonts made possible. To describe the character outlines, they use the third-degree Bézier curves that are common in PostScript, second-degree Bézier curves that are not directly supported by PostScript's graphic model.
Support for CJK TrueType fonts was added in the 2015 version of PostScript.

literature

  • Adobe Systems Incorporated: Adobe Type 1 Font Format. Addison-Wesley, Reading, Mass. 1990, ISBN 0-201-57044-0

Web links

Individual evidence

  1. ^ Adobe Systems Incorporated: PostScript language reference manual. 3rd edition. Palo Alto 1999, p. 357 ff.