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                                                      505
           SECTION 6.4                                                                      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             (Optional) The type of PDF object that this dictionary describes; if present,
                                   must be Halftone for a halftone dictionary.

HalftoneType      number           (Required) A code identifying the halftone type that this dictionary describes;
                                   must be 5 for this type of halftone.

HalftoneName      byte string      (Optional) The name of the halftone dictionary.

any colorant      dictionary       (Required, one per colorant) The halftone corresponding to the colorant or
name              or stream        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.

Default           dictionary       (Required) A halftone to be used for any colorant or color component that
                  or stream        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.

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