Previous Next

                                                    361
          SECTION 4.9                                                               Form XObjects



          Section 4.9.1, “Form Dictionaries”). The value of this entry is a subsidiary group
          attributes dictionary describing the properties of the group.

          As shown in Table 4.46, every group XObject has a group subtype (specified by
          the S entry in the group attributes dictionary) that determines the format and
          meaning of the dictionary’s remaining entries. Only one such subtype is currently
          defined, a transparency group XObject (subtype Transparency) representing a
          transparency group for use in the transparent imaging model (see Section 7.3,
          “Transparency Groups”). The remaining contents of this type of dictionary are
          described in Section 7.5.5, “Transparency Group XObjects.”

                     TABLE 4.46 Entries common to all group attributes dictionaries
KEY       TYPE               VALUE

Type      name               (Optional) The type of PDF object that this dictionary describes; if present, must
                             be Group for a group attributes dictionary.

S         name               (Required) The group subtype, which identifies the type of group whose at-
                             tributes this dictionary describes and determines the format and meaning of the
                             dictionary’s remaining entries. The only group subtype defined in PDF 1.4 is
                             Transparency ; see Section 7.5.5, “Transparency Group XObjects,” for the re-
                             maining contents of this type of dictionary. Other group subtypes may be added
                             in the future.


    4.9.3 Reference XObjects

          Reference XObjects (PDF 1.4) enable one PDF document to import content from
          another. The document in which the reference occurs is called the containing
          document; the one whose content is being imported is the target document. The
          target document may reside in a file external to the containing document or may
          be included within it as an embedded file stream (see Section 3.10.3, “Embedded
          File Streams”).

          The reference XObject in the containing document is a form XObject containing
          the optional Ref entry in its form dictionary, as described below. This form XOb-
          ject serves as a proxy that can be displayed or printed in place of the imported
          content. The proxy might consist of a low-resolution image of the imported con-
          tent, a piece of descriptive text referring to it, a gray box to be displayed in its
          place, or any other similar placeholder. PDF consumers that do not recognize the
          Ref entry simply display or print the proxy as an ordinary form XObject (see im-

Previous Next