SECTION 6.4
505
Halftones
Type 5 Halftones
Some devices, particularly color printers, require separate halftones for each indi-
vidual colorant. Also, devices that can produce named separations may require
individual halftones for each separation. Halftone dictionaries of type 5 allow
individual halftones to be specified for an arbitrary number of colorants or color
components.
A type 5 halftone dictionary (Table 6.7) is a composite dictionary containing
independent halftone definitions for multiple colorants. Its keys are name objects
representing the names of individual colorants or color components. The values
associated with these keys are other halftone dictionaries, each defining the half-
tone screen and transfer function for a single colorant or color component. The
component halftone dictionaries may be of any supported type except 5.
TABLE 6.7 Entries in a type 5 halftone dictionary
KEY
TYPE
VALUE
Type
name
number
byte string
dictionary
or stream
(Optional)
The type of PDF object that this dictionary describes; if present,
must be
Halftone
for a halftone dictionary.
(Required)
A code identifying the halftone type that this dictionary describes;
must be 5 for this type of halftone.
(Optional)
The name of the halftone dictionary.
(Required, one per colorant)
The halftone corresponding to the colorant or
color component named by the key. The halftone may be of any type other
than 5. Note that the key must be a name object; strings are not permitted, as
they are in type 5 PostScript halftone dictionaries.
(Required)
A halftone to be used for any colorant or color component that
does not have an entry of its own. The value may not be a type 5 halftone. If
there are any nonprimary colorants, the default halftone must have a transfer
function.
HalftoneType
HalftoneName
any colorant
name
Default
dictionary
or stream