Key |
Type |
Value |
---|---|---|
Type |
name |
(Optional) The type of PDF object that this dictionary describes; if present, shall be Halftone for a halftone dictionary. |
HalftoneType |
integer |
(Required) A code identifying the halftone type that this dictionary describes; shall be 1 for this type of halftone. |
HalftoneName |
byte string |
(Optional) The name of the halftone dictionary. |
Frequency |
number |
(Required) The screen frequency, measured in halftone cells per inch in device space. |
Angle |
number |
(Required) The screen angle, in degrees of rotation counterclockwise with respect to the device coordinate system. NOTE Most output devices have left-handed device spaces. On such devices, a counterclockwise angle in device space corresponds to a clockwise angle in default user space and on the physical medium. |
SpotFunction |
function or name |
(Required) A function object defining the order in which device pixels within a screen cell shall be adjusted for different gray levels, or the name of one of the predefined spot functions (see Table 128 ). |
AccurateScreens |
boolean |
(Optional) A flag specifying whether to invoke a special halftone algorithm that is extremely precise but computationally expensive; see Note 1 for further discussion. Default value: false. |
TransferFunction |
function or name |
(Optional) A transfer function, which overrides the current transfer function in the graphics state for the same component. This entry shall be present if the dictionary is a component of a type 5 halftone (see “Type 5 Halftones” in 10.5.5.6 ) and represents either a nonprimary or nonstandard primary colour component (see 10.4, "Transfer Functions" ). The name Identity may be used to specify the identity function. |