CID-Keyed Fonts

Overview

The CID-keyed font file format is the ideal format for fonts with large character sets, such as for Chinese, Japanese, and Korean language fonts. This format is an extension of the Type 1 font format, and (CJK) designed to provide optimal flexibility and performance for use with Adobe Type Manager software, and with PostScript printers and image setters.

The CID-keyed font file format may also be used for Roman fonts with large character sets. While the CID-keyed format does not have a provision for supplying kerning information, the OpenType CID-keyed font format does have such a mechanism.

This document is also available in Chinese, Japanese, and Korean language versions (in hardcopy only, at this time); e-mail fontdevsup@adobe.com for details.

Adobe has done extensive development of Character Collections (i.e. character sets) and CMap (encoding) files to support the majority of industry and national standard character sets and encodings for Chinese, Japanese, and Korean language fonts. This, in turn, makes it relatively easy for font developers to support more markets than they might otherwise be able to address.

Character Collection documents were researched by Adobe and reviewed by industry and national language experts. They contain a super set of all characters needed to support a variety of character sets and encodings for each language. Character Collection documents are available in PDF format, with characters shown as 150-dpi bit map images (see Technical Notes | Fonts).

CMap Files

CMap files, also provided by Adobe (although any vendor may also define their own character collection and CMap files), specify the encodings and may be shared amongst various fonts in a printer or on a user's system.

The CMap files for Chinese, Japanese, and Korean language fonts are sorted by the Character Collection document that they are based on, and include:

• CNS1-0 CMap Files
• GB1-3 CMap Files
• Japan1-4 CMap Files
• Japan2-0 CMap Files
• Korea1-0 CMap Files

CID Support Library Kit (CSL)

The CSL consists of a collection of mostly PostScript language files that provide compatibility for CID-keyed fonts with PostScript printers. Since native-mode support for CID-keyed fonts began in version 2015 of the Postscript interpreter, the CSL must be used on pre-2015 interpreters to convert a CID-keyed font into a OCF (original composite font) data structure in the printer. It is also used on version 2015 or greater printers to re-define certain operators, and to allow a CID font to act as a composite font in the case where an application only supports the OCF format.

Under ordinary circumstances, the CID-keyed font vendor will supply its customers with the CSL, which should be downloaded and installed by the font package's installation utility. The CSL may also be provided by a provider of CID font editing tools. The CSL must be installed and updated using a strictly controlled procedure as described in Technical Note #5174, "CID-Keyed Font Installation for PostScript File Systems."

The CSL is available for licensing (at no charge) from the Adobe Solutions Network. The CSL is licensed to font developers for them to include in their CID-keyed font packages; neither a font downloader or installer is provided by Adobe Systems.

For more information on the CID Support Library Kit (CSL), please e-mail: csldevsup@adobe.com

Free Korean CID-Keyed Font
Adobe offers a free Korean CID-keyed font (which can be obtained by ftp) which was made from data supplied by the Korean Ministry of Sports and Culture. It contains 2350 hangul characters; the only restriction is that it cannot be shipped with a commercial product.

Munhwa Regular Korean CID-keyed font
Two versions of the font are available: one is a plain CID-keyed font -- but there is no Macintosh suitcase or Windows PFM file to enable it to be used with ATM on a host computer. The other is an "sfnt-wrapped" CID-keyed font - which can be used on a Macintosh system with an appropriate language kit installed.

This font is available from: ftp://ftp.ora.com/pub/examples/nutshell/ujip/adobe/samples/ (remember to transfer CID-keyed fonts in binary mode!)

Commercial CID-Keyed Font Tools
FontLab Composer is a full-featured CID-keyed font creation tool available from Pyrus North America.

Q & A

Can the CID-keyed format be used for large Latin fonts?
Yes, the CID-keyed format will be very useful for large Roman fonts. CID-keyed fonts are a useful means of including a large number of accented characters, symbols, and the "Expert" characters (small caps, old style figures, fractions, etc.) that are usually packaged in separate fonts. This approach would also allow the developer to specify kerning values between pairs of characters where the first character is in the regular font, and the other character is in the Expert font.

Although such a CID-keyed font containing Roman characters could be built today, it may not be useable in current applications under the English language versions of Windows and Macintosh. The ultimate solution will be CID-keyed versions of OpenType fonts, which will be supported in future versions of the Windows and Macintosh operating systems.

What about kerning for CID-keyed fonts?
The best way to do kerning for CID-keyed fonts would be to use the OpenType font format. The CID-keyed format is really a file organization format, and as such does not have a provision for kerning, and PFM files (for example) only support kerning for 256 characters.

Can I use CID-keyed fonts on a printer without a hard disk?
ATM software will download bit maps of characters to both non-PostScript language printers and to PostScript-language printers without a hard disk. However, performance is much better on PostScript printers with a hard disk attached.

Which version of ATM can CID-keyed fonts be used with?
ATM 3.9 for the Macintosh, and version 3.2J for Windows, both support CID-keyed fonts.

How should CJK ideographic characters be positioned in the em space?
It is important to position characters in the 1000 x 1000 (character space unit) em space so that they are centered in an em square that goes from (0, -120) to (0, 880) in the vertical direction, and from -500 to +500 units in the horizontal direction. This is important so that fonts from different vendors will align vertically when the writing mode is horizontal.

Are there any font naming conventions for CID-keyed fonts?
Yes, they are described in: Adobe Technical Note #5088 " Font Naming Issues" (see Technical Notes | Fonts)

Do CJK ideographic characters require the same kind of hint information as is used for Roman fonts?
Yes, basic hint information is handled in a similar manner. However, there are some special considerations:

The BlueValues array (for vertical alignment) is required, and must not be empty (i.e. with no values between the brackets). The values should be set to y values that are just outside the font bounding box (but not within "BlueFuzz" units of the FontBBox value, and not excessively far away). A typical example might be to declare alignment zones for y=-300, to y=1400. Note, however, that this example is for the case where one hint dictionary is used for an entire CJK font. Ideally, multiple hint dictionaries should be used for the Roman characters, with correct BlueValues so those characters will align correctly.

The LanguageGroup keyword should be set to a value of 1.

RoundStemUp should be defined to have either a true or false value, but the keyword should be there.

Counter Control hints are not required, but help the renderer yield better results and performance if they are included. For details see Adobe Technical Note #5015, "Type 1 Font Format Supplement" (see Technical Notes | Fonts)

Related References

Related Books:
Understanding Japanese Information Processing. Ken Lunde, O'Reilly & Associates, 1993.

Related Web Sites:
Info Document on CJK Font Issues