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What a CID-keyed font is

CID refers to CID-keyed fonts, a PostScript font technology created by Adobe to handle very large character sets, especially the tens of thousands of characters used in Chinese, Japanese, and Korean typography. CID stands for character identifier, the number used to index glyphs.

Instead of naming each glyph, a CID-keyed font references glyphs by numeric identifier and organises them against a character collection that maps encodings to those identifiers. This structure was essential for East Asian fonts, where the sheer number of glyphs made the traditional name-based approach impractical.

Strengths and limits

CID-keyed fonts scale to enormous glyph counts efficiently, which made them the practical way to build professional Chinese, Japanese, and Korean typefaces, and the technology carried forward into OpenType CJK fonts.

The technology is specialised and closely tied to the PostScript and OpenType CFF world, so it is not something general users handle directly. Modern CJK fonts usually deliver this capability through OpenType, which incorporates CID-keyed structures internally.

Origin and Evolution of CID

CID-keyed fonts were developed by Adobe in the early 1990s to address the need for extensive character support in East Asian languages. The technology emerged from the limitations of existing font formats, which struggled to manage the vast number of glyphs required for Chinese, Japanese, and Korean scripts. CID provided a systematic way to index these glyphs using numeric identifiers, allowing for efficient storage and rendering.

The adoption of CID-keyed fonts expanded with the rise of digital typesetting in the 1990s. Adobe standardized the format, leading to its integration into various publishing workflows. Tools such as Adobe Font Folio and later OpenType expanded on CID technology, allowing for enhanced functionality and compatibility across different platforms. This evolution solidified CID's role in professional typography and paved the way for modern font technologies.

Choosing and Using CID

Select CID-keyed fonts when working with large CJK character sets, especially when high-quality typesetting is required. CID fonts are particularly beneficial for projects that involve extensive multilingual text. When converting to or from CID, be aware of differences in encoding and glyph mapping, as these can lead to compatibility issues with non-CID systems.

When using CID fonts, ensure that your design software supports the format to avoid rendering issues. Common workflows include using CID fonts in Adobe InDesign or Illustrator. Be cautious with font management tools, as some may not fully support CID. For conversion, tools like FontForge can assist, but always verify the output to ensure glyph integrity and proper character mapping.

Working with CID-keyed fonts

You will encounter CID-keyed fonts in professional East Asian typesetting and as the internal structure of large OpenType CJK fonts.

For general use, work with the font as an OpenType (OTF) file, which is what applications expect. Font-editing tools can convert between CID-keyed and name-keyed structures when needed for editing.