SECTION 5.6
435
Composite Fonts
In PDF, the CMap and CIDFont are represented by PDF objects, which are de-
scribed below. The CMap and CIDFont programs themselves can be either refer-
enced by name or embedded as stream objects in the PDF file. As stated earlier,
the external file formats are documented in Adobe Technical Note #5014,
Adobe
CMap and CIDFont Files Specification.
A CID-keyed font, then, is the combination of a CMap with a CIDFont contain-
ing glyph descriptions. It is represented as a Type 0 font. It contains an
Encoding
entry whose value is a CMap dictionary, and its
DescendantFonts
entry refer-
ences the CIDFont dictionary with which the CMap has been combined.
5.6.2 CIDSystemInfo Dictionaries
CIDFont and CMap dictionaries contain a
CIDSystemInfo
entry specifying the
character collection assumed by the CIDFont associated with the CMap—that is,
the interpretation of the CID numbers used by the CIDFont. A character collec-
tion is uniquely identified by the
Registry
,
Ordering
, and
Supplement
entries in
the
CIDSystemInfo
dictionary, as described in Table 5.13. Character collections
whose
Registry
and
Ordering
values are the same are compatible.
The
CIDSystemInfo
entry in a CIDFont is a dictionary that specifies the
CIDFont’s character collection. The CIDFont need not contain glyph descriptions
for all the CIDs in a collection; it can contain a subset. The
CIDSystemInfo
entry
in a CMap is either a single dictionary or an array of dictionaries, depending on
whether it associates codes with a single character collection or with multiple
character collections; see Section 5.6.4, “CMaps.”
For proper behavior, the
CIDSystemInfo
entry of a CMap should be compatible
with that of the CIDFont or CIDFonts with which it is used. If they are incompat-
ible, the effects produced are unpredictable.
TABLE 5.13 Entries in a CIDSystemInfo dictionary
KEY
TYPE
VALUE
Registry
ASCII
string
ASCII
string
(Required)
A string identifying the issuer of the character collection—for example,
Adobe
. For information about assigning a registry identifier, contact the Adobe
Solutions Network or consult the ASN Web site (see the Bibliography).
(Required)
A string that uniquely names the character collection within the speci-
fied registry—for example,
Japan1
.
Ordering