GGS extension, HalftoneType 199

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

The RIP supports a HalftoneType, 199, which allows halftone definitions to be shared between (and within) screen sets. This halftone type is useful as a subordinate of a type 5 and type 195 halftones but could, in principle, be used on its own.

This can also save a little time and disk space as the screen's threshold tables or tiles will only be loaded once and the RIP's internal disk cache will be shared.

A halftone of type 199 has only three possible keys (other than HalftoneType), namely:

Halftone

string or name

(Optional) When present, the value identifies an alternative (source) type 5 halftone in which the HalftoneColor is located. (As for OverrideSpotFunctionName, the halftone must be present in switchscreens, that is, one of the standard screens, or introduced as described in Adding extra dot shapes.) When omitted, the alternative screen comes from the type 5 or type 195 dictionary in which the type 199 halftone appears.

HalftoneColor

string or name

(Optional) Uses the halftone for the named color for the screen being defined.

HalftoneObjectType

string or name

(Optional) This is similar to /HalftoneColor, but names the type component of a Halftone type 195 to be used.

If both /HalftoneObjectType and /HalftoneColor are given, the type is looked up first and the color is looked up in the result.

A typical usage of these new caches in sf.ps is this extracted, reformatted, and commented definition for CMYKcm PhotoInk:

% HDS-a6p screen set for PhotoInk printing
/Hds-a6p <<
  /HalftoneType 5
  /HalftoneName /Hds-a6p
  (Photo Cyan) cvn <<
    /HalftoneType 199
    /Halftone /Hds-a-gen % Halftone name (and, for HDS, the folder name)
    /HalftoneColor /A % Color name (and, for HDS, the subfolder)
  >>
  (Photo Magenta) cvn <<
    /HalftoneType 199
    /Halftone /Hds-a-gen
    /HalftoneColor /B
  >>
  (Photo Yellow) cvn <<
    /HalftoneType 199
    /Halftone /Hds-a-gen
    /HalftoneColor /C
  >>
  (Photo Black) cvn <<
    /HalftoneType 199
    /Halftone /Hds-a-gen
    /HalftoneColor /D
  >>
  (Photo Cyan Light) cvn << % Used in conjunction with Photo Cyan
    /HalftoneType 199
    /Halftone /Hds-a-gen
    /HalftoneColor /Ai % Uses the complement to A, used for Photo Cyan
  >>
  (Photo Magenta Light) cvn << % Used in conjunction with Photo Magenta
    /HalftoneType 199
    /Halftone /Hds-a-gen
    /HalftoneColor /Bi % Uses the complement to B, used for Photo Magenta
  >>
  /Default << % Used for spot colors not explicitly named
    /HalftoneType 199
    /Halftone /Hds-a-gen
    /HalftoneColor /Default % Uses the Default from the source halftone
  >>
>> def

There is no TransferFunction key. Transfer functions are always attached to the dictionary that actually defines the halftoning patterns. In order to set a transfer function, you have to give up on using type 199, take the dictionary referenced, and make a modified copy of it with the transfer function added. This is a useful technique with our HDS and AIS screens, which are normally defined using type 199 to pick the components from the large selection of screens supplied. For further information see the Harlequin Technical Note Hqn096: Advanced Inkjet Screens for HHR .