Previous Next

                                                    275
          SECTION 4.5                                                                  Color Spaces



KEY             TYPE           VALUE

DotGain         dictionary     (Optional) A dictionary specifying the dot gain of inks to be used in blending
                               calculations when used as an alternative to the tint transformation function.
                               Dot gain (or loss) represents the amount by which a printer’s halftone dots
                               change as the ink spreads and is absorbed by paper.
                               For each entry, the key is a colorant name, and the value is a function that maps
                               values in the range 0 to 1 to values in the range 0 to 1. The dictionary may list
                               colorants unused by this specific DeviceN instance and need not list all colo-
                               rants. An entry with a key of Default specifies a function to be used by all colo-
                               rants for which a dot gain function is not explicitly specified.
                               PDF consumer applications may ignore values in this dictionary when other
                               sources of dot gain information are available, such as ICC profiles associated
                               with the process color space or tint transformation functions associated with
                               individual colorants.

          Each entry in the mixing hints dictionary refers to colorant names, which include
          spot colorants referenced by the Colorants dictionary. Under some circumstanc-
          es, they may also refer to one or more individual process components called
          Cyan, Magenta, Yellow, or Black when DeviceCMYK is specified as the process col-
          or space in the process dictionary. However, applications should ignore these pro-
          cess component entries if they can obtain the information from an ICC profile.

          Note: The mixing hints subdictionaries (as well as the colorants dictionary) may
          specify colorants that are not used in any given instance of a DeviceN color space.
          This allows them to be referenced from multiple DeviceN color spaces, which can
          produce smaller file sizes as well as consistent color definitions across instances.

          For consistency of color, PDF consumers should follow these guidelines:

          • The consumer should apply either the specified tint transformation function or
            invoke the same alternative blending algorithm for all DeviceN instances in the
            document.
            Note: When the tint transformation function is used, the burden is on the produc-
            er to guarantee that the individual function definitions chosen for all DeviceN in-
            stances produce similar color appearances throughout the document.
          • Blending algorithms should produce a similar appearance for colors when they
            are used as separation colors or as a component of a DeviceN color space.

Previous Next